Posts Tagged Brain stimulation

[WEB PAGE] Mozart’s piano music can reduce the frequency of epilepsy attacks

A new comprehensive analysis on the effect of Mozart’s music on epilepsy has confirmed that listening to his piano music can reduce the frequency of epilepsy attacks. The results of this comprehensive meta-analysis (a study of studies), which may overturn current scepticism about the effect, are presented at the ECNP congress after recent publication in a peer-reviewed journal.

The idea that listening to Mozart may have beneficial effects on mental health arose from early findings in the 1990s. There have been several studies since, but many involved small numbers of people, or have been of variable quality, leading to mixed evidence overall. This has meant that the “Mozart Effect” has been treated with some scepticism by many clinicians.

Now two Italian Researchers, Dr Gianluca Sesso and Dr Federico Sicca from the University of Pisa have conducted a systematic review of works related to the effect of Mozart’s music on epilepsy.

Working according to accepted standard methods for analysing clinical treatment, they looked at 147 published research articles, which they then evaluated according to such things are relevance and quality of the research. This allowed them to select 12 pieces of research which they gathered into 9 separate groups, representing the best available science on the effect of Mozart’s music on epilepsy.

They found that listening to Mozart, especially on a daily basis, led to a significant reduction in epileptic seizures, and also to a reduced frequency of abnormal brain activities in epileptic patients (called interictal epileptiform discharges, which are commonly seen in epileptic patients). These effects occurred after a single listening session and were maintained after a prolonged period of treatment.

Gianluca Sesso said “This isn’t the first such review of the effect of Mozart’s music on epilepsy, but there has been a flow of new research in the last few years, so it was time to stand back and look at the overall picture. The design of the studies varies, for example some people look at a single listening session, others at daily listening sessions, so it’s not easy to form a conclusion.


Epilepsy is surprisingly common, affecting just under 1 person in a hundred worldwide. This means that it has significant social and personal costs. Mostly it’s treated by drugs, but these drugs don’t work in around 30% of patients, so we need to be open to other therapies: the important thing is that these therapies can be tested and shown to work, and this is what we have shown here”.

The meta-analysis indicates that a period of listening to Mozart can give an average reduction in epileptic seizures ranging from between 31% to 66%, but this varies from person to person and according to the music stimulus used. The original studies on the Mozart Effect used the sonata for 2 pianos, K448, and this has remained the music most used in studies. The K545 piano sonata has also been shown to have an effect.

Dr Sesso said “All cultures have music, so it obviously fulfils some psychological need. The mechanisms of the Mozart Effect are poorly understood. Obviously other music may have similar effects, but it may be that Mozart’s sonatas have distinctive rhythmic structures which are particularly suited to working on epilepsy. This may involve several brain systems, but this would need to be proven.

This is a review of research, and not original research. One thing it shows is that we need more consistent studies into the effect of music on the mind”

Commenting, Dr Vesta Steibliene, Lithuanian University of Health Sciences, and member of the ECNP Abstract and Poster Committee said:

“There is growing interest in non-invasive brain stimulation techniquesin the treatment of neuropsychiatric disorders. This review revealed that Mozart music could be an effective non-invasive method of neurostimulation, reducing the frequency of epileptic seizures, even in hard to treat patients. However, in order to use this method in clinical settings, the exact mechanism of the Mozart music effect on the brain regions should be better understood”.

Source: European College of Neuropsychopharmacology (ECNP)

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[WEB PAGE] Individual frequency can be used to control brain activity – News

Reviewed by Emily Henderson, B.Sc.Aug 17 2020

Individual frequency can be used to specifically influence certain areas of the brain and thus the abilities processed in them – solely by electrical stimulation on the scalp, without any surgical intervention. Scientists at the Max Planck Institute for Human Cognitive and Brain Sciences have now demonstrated this for the first time.

Stroke, Parkinson’s disease and depression – these medical illnesses have one thing in common: they are caused by changes in brain functions. For a long time, research has therefore been conducted into ways of influencing individual brain functions without surgery in order to compensate for these conditions.

Scientists at the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany, have taken a decisive step. They have succeeded in precisely influencing the functioning of a single area of the brain. For a few minutes, they inhibited exactly the area that processes the sense of touch by specifically intervening in its rhythm. As a result, the area that was less networked with other brain regions, its so-called functional connectivity, decreased, and thus also the exchange of information with other brain networks.

This was possible because the researchers had previously determined each participant’s individual brain rhythm that occurs when perceiving touch. With the personal frequency, they were able to modulate the targeted areas of the brain one at a time in a very precise manner using what is known as transcranial alternating current stimulation. “This is an enormous advance,” explains Christopher Gundlach, first author of the underlying study. “In previous studies, connectivity fluctuated extensively when the current was distributed in different areas of the brain. The electrical current randomly sought its own path in the brain and thus affected different brain areas simultaneously in a rather imprecise manner.

In a preliminary study, the neuroscientists had already observed that this form of stimulation not only reduces the exchange of the targeted brain networks with other networks, it also affects the brain’s ability to process information, in this case the sense of touch. When the researchers inhibited the responsible somatosensory network, the perception threshold increased. The study participants only perceived stimuli when they were correspondingly strong. When, on the other hand, they stimulated the region, the threshold value dropped and the study participants already felt very gentle electrical stimuli.

The deliberate change in brain rhythm lasted only briefly. As soon as the stimulation is switched off, the effect disappears again. Nevertheless, the results are an important step towards a targeted therapy for diseases or disorders caused by disturbed brain functions”.

Bernhard Sehm, Study Leader

Targeted brain stimulation could help to improve, direct and, if necessary, attenuate the flow of information.

Source: Max Planck Institute for Human Cognitive and Brain Sciences

Journal reference: Gundlach, C., et al. (2020) Reduction of somatosensory functional connectivity by transcranial alternating current stimulation at endogenous mu-frequency.  NeuroImage. doi.org/10.1016/j.neuroimage.2020.117175.

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[ARTICLE] Enhancing cognitive control training with transcranial direct current stimulation: a systematic parameter study – Full Text

Abstract

Background

Cognitive control (CC) is an important prerequisite for goal-directed behaviour and efficient information processing. Impaired CC is associated with reduced prefrontal cortex activity and various mental disorders, but may be effectively tackled by transcranial direct current stimulation (tDCS)-enhanced training. However, study data are inconsistent as efficacy depends on stimulation parameters whose implementations vary widely between studies.

Objective

We systematically tested various tDCS parameter effects (anodal/cathodal polarity, 1/2 mA stimulation intensity, left/right prefrontal cortex hemisphere) on a six-session CC training combined with tDCS.

Methods

Nine groups of healthy humans (male/female) received either anodal/cathodal tDCS of 1/2 mA over the left/right PFC or sham stimulation, simultaneously with a CC training (modified adaptive Paced Auditory Serial Addition Task [PASAT]). Subjects trained thrice per week (19 min each) for two weeks. We assessed performance progress in the PASAT before, during, and after training. Using a hierarchical approach, we incrementally narrowed down on optimal stimulation parameters supporting CC. Long-term CC effects as well as transfer effects in a flanker task were assessed after the training period as well as three months later.

Results

Compared to sham stimulation, anodal but not cathodal tDCS improved performance gains. This was only valid for 1 mA stimulation intensity and particularly detected when applied to the left PFC.

Conclusions

Our results confirm beneficial, non-linear effects of anodal tDCS on cognitive training in a large sample of healthy subjects. The data consolidate the basis for further development of functionally targeted tDCS, supporting cognitive control training in mental disorders and guiding further development of clinical interventions.

 

Introduction

Continuously changing environments require dynamic adaptation by means of filtering and evaluating internal and external stimuli to orchestrate goal-directed behaviour. This is especially important for situations in which distractions might influence efficient responses. Important information is maintained, while non-relevant stimuli must be suppressed or ignored. Dysfunctions of cognitive control (CC) processes are at the core of many psychopathological conditions [1,2], comprise the intentional selection of thoughts, emotions, and behaviours based on current task demands [3] involving functions of attention, memory, and emotional control [4], and are associated with altered patterns of brain activation [5,6]. The prefrontal cortex (PFC), particularly the dorsolateral prefrontal cortex (dlPFC), is known to be highly involved in CC processes [7] by means of processes related to working memory [8], encoding of task relevant rules and responses [9], and emotion regulation [10].

Transcranial direct current stimulation (tDCS) has been put forward as a means to influence these processes by modulating the likelihood of neuronal firing in response to a stimulus [11]. At the macroscopic level, within the common and safe range of stimulation parameters (1–2 mA, up to 30 min of stimulation [12]), it is supposed that anodal tDCS predominantly enhances, while cathodal tDCS mainly reduces the excitability and spontaneous activity of the targeted and connected areas [13]. This polarity-dependent modulation of brain activity by tDCS has a remarkable potential to influence corresponding cognition and behaviour [[14][15][16]]. However, tDCS does not induce cortical activity per se. It develops its effects particularly in interaction with spontaneous neuronal activity [17,18]. This activity-dependent influence on brain networks allows for a ‘functional targeting’ of stimulation when tDCS is directly coupled with the respective cognitive or behavioural process [19], where the target regions are activated (i.e. by a task) and further specifically modulated by the stimulation [20]. Correspondingly, tDCS effects have been found especially in neuronal correlates of task features that were active during stimulation [21]. Therefore, the combination of tDCS with task training is suggested to have a synergistic ‘neuroenhancing’ effect that is currently subject of extensive research [[22][23][24][25]]. However, available data are still inconsistent as efficacy depends on stimulation parameters that vary widely between studies. For a meaningful clinical application, a sustainable enhancement of adaptive plasticity would be most desirable [26]. Based on this notion, a specific activation of the CC network and concomitant tDCS holds promise to provide new treatment strategies for cognitive and behavioural disorders [[27][28][29]]. In a plethora of studies, stimulation has already shown to enhance CC by changing emotion regulation processes [30], improving frustration tolerance [31], modulating emotional vulnerability [32], dissolving attentional biases [33], augmenting working memory training [16], and increasing multitasking capacity [34]. However, reliability of results and the plausibility of approaches leaves room for improvement, not at least because studies often yield varying results even for similar tasks [[35][36][37][38]]. Therefore, reliable knowledge about the efficacy of parameter settings is mandatory for further advancements [39].

To this aim, we systematically tested different standard stimulation parameters (anodal/cathodal tDCS with 1/2 mA to the left/right dlPFC) in 162 healthy subjects, combining repeated CC training (6 sessions within 2 weeks) with tDCS, and additionally analysed pre- and post-training assessments. We applied a modified adaptive paced auditory serial addition task (PASAT) to challenge and train CC [40]. This task requires continuous updating of working memory with parallel distracting performance feedback; it is known to activate CC [31], critically involves resources within the PFC [41], and adapts task difficulty to individual performance [42]. We hypothesized that adding anodal but not cathodal tDCS to PASAT-induced neuronal activity of the dlPFC [43,44] can enhance cognitive training effects [45,46], improve performance of the PASAT or similar, even more challenging tasks [16,31,[46][47][48][49][50]], and that higher stimulation intensity does not increase efficacy [51]. Furthermore, we wanted to test if the laterality of stimulation matters. Therefore, PASAT performance under eight different tDCS conditions (combined N = 119) was compared to a sham intervention group (N = 43). Analyses were conducted hierarchically, allowing us to narrow down the responsible factors for the most efficient combination of CC training and tDCS.[…]

Continue —-> Enhancing cognitive control training with transcranial direct current stimulation: a systematic parameter study – ScienceDirect

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[WEB PAGE] Is Brain Stimulation the Next Big Thing?

Over the past decade, athletes, coaches, and researchers have been seduced by the performance-boosting promises of brain stimulation. On a ride-and-zap-your-brain-like-the-pros tour through the Alps, Alex Hutchinson wonders whether it really works—and whether we want it to.

For the first 20 miles of the ride up the Col du Galibier—the storied Alpine climb that debuted in the Tour de France back in 1911, when all but three riders were forced to dismount and walk their chunky pre-carbon-fiber velocipedes to the 8,000-foot summit—I was actually enjoying myself, more or less. The other cyclists on my weeklong tour had decided to bag it and hop in the support van halfway up the climb, as the temperature began to plummet and a cold rain swept down from the surrounding peaks. So had Massimo, our cheerfully inscrutable, Dante-quoting bike guide, who preferred the warmer climes of his native Sardinia. I was alone with the mountain, savoring the subtle gradations of my rising distress.

With a couple miles to go, though, the novelty started to wear off. The rain turned to sleet, and as I switchbacked through canyon-like passageways formed by monstrous ten-foot snowbanks, my hands, in their sodden gloves, became too numb to operate my gears—more of a theoretical problem than an actual one, since I was too spent to get out of my lowest gear anyway. As I neared the summit, the grade seemed to keep getting steeper, the headwind stronger, and my insistence on finishing the climb under my own power more foolish.

Instead of the ghosts of Coppi and Merckx and other bygone stars who’d triumphed here, I found myself chasing the flowing locks of Fabian Cancellara, the flamboyant Swiss rider who was famously (some would say outrageously) accused of hiding a tiny electric motor in his bike in 2010. As a novice cyclist embarking on an ambitious itinerary called Epic Climbs of the Western Alps, I had seriously considered requesting one of the e-bikes offered by my tour company, just to make sure I wouldn’t hold my more experienced trip mates back. Now I contemplated Fabian’s choice: If I had a Go button on my bike, would I press it?

A winding road from the French town of Briançon leads up to Col d’Izoard at 7,743 feet, a pass that frequently features in the Tour de France as a climb rated hors catégorie.
A winding road from the French town of Briançon leads up to Col d’Izoard at 7,743 feet, a pass that frequently features in the Tour de France as a climb rated hors catégorie. (Photo: Edoardo Melchiori)

As I turned yet another corner, with less than half a mile to go, the easterly headwind became a virtual wall. I had to get out of my saddle and lean into a wobbly, slow-motion sprint just to avoid slowing to a complete halt and toppling over sideways. By the time I turned away from the wind a few hundred yards later, my heart rate and breathing were fully maxed out and my legs were jelly. I knew I couldn’t face the gale again. Then I saw that, instead of another hairpin, the road ahead snaked up the rest of the way to the summit without turning back into the wind. I pedaled onward, with a mix of pride and relief—pride that I’d made it, relief that my bike hadn’t, after all, been equipped with a motor that would have tempted me to take an electric shortcut.

A few minutes later, I was thawing in a cozy bistro on the far side of the summit, sipping hot chocolate, with a plush hotel-style bathrobe draped over my shivering shoulders. That’s when an uncomfortable thought struck me: Why should I disparage the boost provided by an electric motor when, that very morning, with precisely the same goal, I’d sat patiently in a hotel lounge while a neuropsychologist trickled electric current through a web of electrodes gelled to my scalp?


Really it was just a matter of time. Back in 2013, when Brazilian scientists first showed that a relatively simple protocol of transcranial direct-current stimulation (tDCS) to the brain seemed to enhance endurance, you could already map out the events that would follow: the flood of copycat studies, the launch of a Silicon Valley startup peddling the technique to early adopters, the murky reports of professional athletes and teams like the Golden State Warriors and the U.S. ski squad experimenting with it, the rising ethical concerns about fairness and safety, and, finally, the press release that showed up in my inbox in January of this year—the field’s “Holy shit, they’re using Crispr on human embryos!” moment.

The pitch was from NeuroFire Cycling, a spin-off of Bahrain Merida Pro Cycling Team’s official sports-medicine clinic, the RIBA Rehabilitation Institute (IRR), based in Turin, Italy. It had enlisted a bike-touring company called Tourissimo, also based in Turin, to run the logistics for a bespoke trip, giving well-heeled amateurs the opportunity to spend a week riding famous Grand Tour passes while eating gourmet meals and receiving “advanced neurostim protocols used by the world’s top riders” for a cool $7,000 plus airfare. Before tackling the Colle delle Finestre, in the Piedmontese Alps of northern Italy, you’d get your prefrontal cortex stimulated to “enhance performance, mood, and the propensity to enter flow states.” After the Col d’Izoard, across the border in France’s Hautes-Alpes region, you’d hit your upper motor cortex “to enhance the central nervous system’s role in natural recovery processes.”

It read like an elaborate piece of satire. But it’s not: the technology is, on at least some level, real, and after six years of speculation and hype, someone was bound to start promoting it to the recreational market. It occurred to me that a tour for weekend warriors run by scientists also working with a top UCI cycling team would offer a unique opportunity to delve into some of the lingering questions about tDCS. Not just the obvious ones—does it work? is it safe?—but also trickier ones about fairness, technological innovation, and the deeper meaning of sport for those of us whose wins and losses are personal and unremunerated. So in early June, I buckled into a red-eye to Turin for a week of hard climbs, fine wines, and credulity-stretching neuroelectrophysiology.

The technology is, on at least some level, real, and after six years of speculation and hype, someone was bound to start promoting it to the recreational market.

The idea that a jolt to your brain might enhance your physical powers isn’t quite as futuristic as it sounds. A history of tDCS published in Psychological Medicine in 2016 traces the technique’s lineage back to Roman times, when an imperial physician named Scribonius Largus prescribed a live torpedo fish to the scalp to relieve headaches. Similar ideas crop up in cultures around the world, but the modern incarnation of tDCS began in the late 1990s and took off a decade or so later. The basic idea is simple: your brain is like a vast interconnected circuit, with neurons that communicate with each other via electric discharges. Applying a very weak current of a few milliamperes tweaks the excitability of the affected neurons, such that they become a little more (or, if you run the current in the opposite direction, less) likely to fire in response to whatever you do in the subsequent hour or two. Exactly what that means depends on which parts of the brain you hook up, but the general upshot is that different brain regions are able to communicate with each other more easily—which, if you believe the hype, can have effects ranging from changing your mood to making you a better sniper. All it takes, as a vibrant and somewhat scary online DIY subculture attests, is a nine-volt battery and a couple of electrodes.

Of course, wiring up your brain still carries some pretty weighty cultural associations. When Massimo, the Tourissimo cycling guide, picked me up at the airport, I found that he was as bemused by the whole thing as I was. As we dodged and weaved through Turin’s Saturday-morning traffic, he outlined the plan: he would take me back to the hotel for lunch and a brief rest, then I’d get fitted for a bike, then he would take me to the IRR clinic for my first—as he described it, air quotes and all—“treatment.” I’d be joined by two other cycling journalists from Britain for NeuroFire’s maiden tour, he said, since no paying customers had actually signed up. Still, “we have another testimonial,” he added cheerfully. “It’s from Jack Nicholson.”

At the clinic, a sleek complex with ultramodern furniture, rows of sophisticated rehab equipment, and the high-wattage brightness of a toothpaste commercial, we met a half dozen members of the tour’s medical and support staff. The plan for the week, they explained, had two main parts. For our first three days of cycling, we would receive 20 minutes of brain stimulation immediately before riding, with the electrodes positioned on our scalp in a configuration designed to enhance our performance, perhaps by kicking us into a flow state for the first hour or two of the ride. For the last two days, as the cumulative fatigue of tens of thousands of feet of climbing mounted, we would switch to 20 minutes of stimulation immediately after riding, this time with an electrode configuration chosen to enhance the recuperative powers of the massage we would receive simultaneously as our synapses sizzled.

But first we needed some baseline testing to figure out where the electrodes should be placed on each of us. A neuropsychologist from the IRR named Elisabetta Geda ushered me down a corridor, past rows of glossy pamphlets and posters displaying before-and-after tummy pics from exotic treatments like “full-body contouring by cryoadypolisis,” to a quiet room where she pulled a neoprene cap studded with electrodes over my scalp. As I visualized cycling up a mountain road, she used electroencephalography (EEG) to monitor the communication between different regions of my brain. “The brain signals are like an orchestra,” she explained. “Every section has a rhythm, and we record these rhythms with EEG. Then we can personalize your electrode montage, because each person may need a different treatment.”

Geda and her colleagues at the rehabilitation clinic have been using tDCS for several years on patients with conditions like chronic pain, addiction, fatigue related to multiple sclerosis, and cognitive deficits after traumatic brain injury. They use it in combination with existing treatments, priming the appropriate neurons to fire more readily in order to amplify the benefits of those therapies. So in 2017, when the IRR signed on as the official sports-medicine provider for the new Bahrain Merida cycling team, Geda began to consider the technique’s athletic potential. She and her collaborators ran a study replicating the 2013 Brazilian results, then floated the idea to Bahrain Merida.

The initial response was lukewarm. “At the beginning, we were a little bit afraid,” Luca Pollastri, one of the cycling team’s medical doctors told me. “We took some time to understand what’s going on, what’s legitimate, what’s the World Anti-Doping Agency’s position, and so on.” Instead of using it to directly enhance performance, Pollastri asked Geda if she could devise a protocol that would help athletes relax and recover after racing, which is a major challenge in Grand Tours, when riders are going to the well day after day for weeks. Geda suggested stimulating the brain during massage, effectively amplifying the massage’s effects on the central nervous system—an unorthodox approach that no one else had tried.

Neuropsychologist Elena Fontana, from the RIBA Rehabilitation Institute, wires up the author for a session of transcranial direct-current stimulation (tDCS) after a long day of riding.
Neuropsychologist Elena Fontana, from the RIBA Rehabilitation Institute, wires up the author for a session of transcranial direct-current stimulation (tDCS) after a long day of riding. (Photo: Edoardo Melchiori)

Among the first riders to try it was Domenico Pozzovivo, an Italian climbing specialist known in the peloton as the Doctor for his cerebral approach—not Bahrain Merida’s star, but someone happy to experiment with new ideas and capable of giving detailed feedback about them. In the 2018 Giro d’Italia, Pozzovivo started using tDCS to boost his recovery a few stages into the race. Night after night, he faithfully donned the electrodes for a massage, and after 17 stages, he found himself in third position in the general classification: on track, at age 35, for his first-ever Grand Tour podium. But the complicated logistics of a grueling mountaintop finish in the resort town of Prato Nevoso meant that he missed his session after the 18th stage, and, for the first time in the race, he slept poorly. The next day, he lost eight minutes to the leader and slipped back to sixth overall, before rallying in the final two stages to finish fifth. To the staff at Bahrain Merida, and to Pozzovivo himself, neither his career-best overall performance nor the timing of his one bad day seemed like a coincidence.

By this time, Pollastri and his colleagues were ready to consider using the technique as a prerace booster. With Gabriele Gallo, a sports scientist at the University of Milan, they brought ten cyclists from Bahrain Merida’s continental team to the lab for a double-blind series of simulated 15-kilometer time trials with real and sham tDCS. For a roughly 20-minute effort, the riders averaged 16 seconds faster with tDCS, right on the margins of a statistically significant improvement. It was suggestive enough that they decided to use it at the opening stage of the 2019 Tour de Romandie, where Slovenian rider Jan Tratnik took the win for Bahrain Merida.


On the morning after our EEG tests, we met Geda in a conference room in the imposingly ornate Grand Hotel Sitea for our first treatment before a test ride up the Colle della Maddalena, one of the hills across the Po River from downtown Turin. When I apologized for encroaching on her Sunday, Geda waved me off: she’d sent her two toddlers to their grandmother’s for the weekend so she could focus on the tour. “This is like a holiday for me,” she laughed. Pulling up a 3-D model of the human brain on her computer, she outlined the results of the previous day’s EEG tests.

Trevor Ward, one of the British journalists, apparently had “a great connection” between his prefrontal and motor cortices—between perception and action, in effect. This is characteristic of elite athletes, Geda explained, so he would receive the same six-electrode tDCS stimulation that the pros got, focusing on the prefrontal cortex (PFC) itself. That’s the region of the brain that integrates information from everywhere else and decides whether and when you can push harder. “Our theory is that the PFC is less active during exercise because other regions are overloaded,” Gallo explained. “So if we stimulate this area, the athlete should have better regulation of pacing.”

The other Brit, John Whitney, and I were not so accomplished, so we’d get a remedial eight-electrode stimulation to help nurture the crucial prefrontal-motor connection in addition to stimulating the PFC. Geda slid the neoprene cap onto my head, and I felt a mild prickling in my scalp as one milliampere of current began to flow. A minute or so later, the sensation faded to nothing, and for the rest of the 20 minutes, I simply sat back and relaxed.

After a short ride through the cobbled maze of Turin’s pedestrian core (and the requisite stop for espresso), we crossed the Po and started climbing. As we pedaled up the incline, I felt a little buzzed and a little jet-lagged, and my bike felt about half as heavy as usual—which it was, since I’d trained for the trip on an aging mountain bike and was now riding a $6,000 carbon-frame Bianchi. Joining us for the ride was Vittoria Bussi, the reigning world-record holder for the one-hour time trial, and I fell in beside her to get her take on the technology.

I felt a little buzzed and a little jet-lagged, and my bike felt about half as heavy as usual—which it was, since I’d trained for the trip on an aging mountain bike and was now riding a $6,000 carbon-frame Bianchi.

Bussi, it turned out, had just returned from a time trial in Slovenia, where she’d been accompanied by Geda to try prerace tDCS. Bussi hadn’t detected any difference in performance or power output, but her heart rate had been lower than usual—a somewhat ambiguous result that she’d also noticed in a previous experiment with the technique. A compulsive tinkerer, with a Ph.D. in math from the University of Oxford, Bussi saw tDCS as just another element of the continual process of experimentation, quantification, and optimization that cycling permits. “I’m curious,” she said. “I like trying to figure out the best possible approach to a problem.” Overall, the race in Slovenia had been a success, with a third-place finish that boded well for her goal of qualifying for the 2020 Olympics. She figured she’d keep using brain stimulation, at least for a while.

As for me—well, I never expected to feel any magical gains from brain stimulation. (Don’t tell my editor.) My pace up the Colle della Maddalena, or any other hill, would be determined by how hard it felt. If the effort that felt sustainable happened to get me to the top a percent or two faster than normal, how would I possibly detect such a subtle difference? At best, the cumulative effects of each day’s brain stimulation would leave me a little fresher as the week (and its 37,000 feet of climbing) proceeded—better able to enjoy the evening feasts, less likely to end up in the sag wagon. But for any given ride, the only useful way to judge something like this is with well-designed research, preferably double-blind and peer-reviewed. Trust the data, not your easily deluded intuition.


Even the data, however, is far from definitive on tDCS. The U.S. National Library of Medicine lists more than 5,000 tDCS studies, the vast majority from the past decade. The technique improves working memory (or maybe it doesn’t), it helps patients with Parkinson’s disease walk better (or maybe it doesn’t), it helps fight depression (or maybe it doesn’t), and on and on for a seemingly limitless variety of conditions. There’s a ton of hype and a corresponding amount of backlash. One researcher described the field as “a sea of bullshit and bad science.”

The sports applications of tDCS face a similarly muddled situation. A review published in Frontiers in Physiology in 2017 identified 12 studies of brain stimulation and exercise performance, eight of which found a performance boost. Conversely, two meta-analyses of 22 and 24 studies published in Brain Stimulation in 2019 concluded that the evidence in favor of an athletic boost is somewhere between slim and nonexistent. Part of the problem is that different studies use different protocols, electrode montages, and exercise tests. Some stimulate the motor cortex, hoping to facilitate a stronger output signal from brain to muscle. That’s the approach that consumer-tech startup Halo Neuroscience uses for its $400 brain-stimulating headphones. Other studies stimulate the regions responsible for evaluating inputs to the brain, hoping to dull the sensation of effort. Geda and Pollastri, by focusing on the prefrontal cortex, take yet another approach.

To skeptics, peering at this hodgepodge of conflicting evidence and concluding that brain stimulation will make you faster sounds a lot like wishful thinking. In July, a postdoctoral researcher at the University of Calgary named James Wrightson posted a preprint (a finished paper that is posted publicly for comment prior to being submitted for peer review) of his latest study, which found no effect of tDCS to the motor cortex on leg endurance. A crucial detail: Wrightson’s study protocol had been preregistered, meaning that he decided in advance how his data would be analyzed, and he committed to sharing the results regardless of whether or not they confirmed his hypothesis. How many of the small, positive reports of tDCS’s athletic effects, he wondered, might be explained by massaged data or counterbalanced by negative studies that no one bothered to publish?

These issues aren’t unique to tDCS research, of course. In fact, they apply to pretty much any sexy and “science-backed” performance aid these days. Wrightson is a passionate advocate of more rigorous methodology in sports science, which lags behind other fields, like neuroscience, in insisting on things like preregistration and large sample sizes that reduce the likelihood of spurious results. His own study, with 22 subjects, isn’t enough to prove that tDCS doesn’t work, he emphasized when I emailed to ask about his research. Many more studies, with far bigger sample sizes, are needed before we can draw any firm conclusions. Until then, his advice to athletes is to skip tDCS—and any other shiny new performance booster—until better evidence is available. “But athletes are always going to be athletes (and coaches, coaches),” he wrote, “so we’ll probably still see Halo devices everywhere at Tokyo 2020 anyway.”

The tDCS protocol used by NeuroFire and the Bahrain Merida cycling team involves electrodes held in place by a neoprene cap, with the current controlled wirelessly from a laptop computer.
The tDCS protocol used by NeuroFire and the Bahrain Merida cycling team involves electrodes held in place by a neoprene cap, with the current controlled wirelessly from a laptop computer. (Photo: Edoardo Melchiori)

From a scientific perspective—the Sisyphean pursuit of knowledge through the eternal evaluation and reevaluation of evidence, let’s say—Wrightson is undeniably correct. We don’t know shit about tDCS, scientifically speaking. But his comment about athletes being athletes, with the implication that anyone who tries an unproven technique like tDCS is a benighted dunce, struck me as unfair. Athletes are not trying to advance human knowledge or settle epistemological questions; they’re trying to win. If you have a technology with minimal cost, no known health risks, and there’s a plausible but unproven chance that it has real performance-boosting effects, isn’t it entirely rational to give it a try? Even ignoring placebo effects—another discussion entirely—there’s a small possibility of life-altering benefits for an elite athlete near the top of their sport, weighed against negligible downsides.

Wrightson, when I put this to him, didn’t buy it. In fact, he felt that even discussing preliminary research in fields like tDCS outside the hallowed halls of academia was highly irresponsible. Writing about tDCS in the “lay press,” as I had done on several occasions (and am doing right now, for that matter), was particularly egregious. “I think you were wrong to publish those articles so early,” he insisted. “It’s a hill I’m willing to die on.”


The first real hill of our tour, on Monday morning, was the Colle delle Finestre—the hero-making climb where, in last year’s Giro, Chris Froome made his winning 50-mile breakaway and where, after a restless night, Pozzovivo’s podium dreams died. We started our day in the Alpine town of Susa, lounging on folding chairs in a public park in the shadow of an imposing 2,000-year-old Roman arch as Geda gelled up the electrodes. But just before she cranked on the current, the ominous clouds above us unleashed a few warning drops. We barely had time to scramble back into the van, where I put in my 20 minutes of stimulation amid the drumbeat of torrential rain on the roof.

An hour later, the rain finally subsided, and we pedaled off, with Massimo setting the pace. We soon settled into a rhythm that would come to feel routine in the days to come, climbing steadily for 10 or 15 or 20 miles at a time, up average grades of 7 or 8 or 9 percent. There was almost no traffic, since other roads and tunnels now provide faster and more direct routes across the mountain passes. We saw nobody other than the occasional shepherd or blueberry picker, though we passed farmhouses and mountain refuges and ancient churches and monuments to cyclists of yore. It’s not like climbing the short, sharp hills that I encounter around my home in Toronto, where you can rely on momentum and a leg-burning sprint to get you to the crest. Instead you have to find a sustainable rhythm, so that the climb becomes not a frantic struggle but a meditative grind.

Just under five miles from the top of Colle delle Finestre, the asphalt ended. The rest of the road was gravel, wet and slippery thanks to the rain that was once again falling. I focused on following Massimo’s rear wheel, weaving between rocks and cutting across stream-washed gullies in the road. I felt surprisingly strong and was almost disappointed when we finally reached the stone monument to cycling star (and thrice-caught doper) Danilo di Luca at the summit. I’d have sworn the brain stimulation had worked, except that the rain-delayed start meant the performance-boosting window—about 90 minutes, Geda had told us—had closed long before we even hit the gravel.

The descent from Colle dell’Agnello, which leads from France back into Italy, passes through quiet, cobbled Piedmontese mountain towns like Chianale.
The descent from Colle dell’Agnello, which leads from France back into Italy, passes through quiet, cobbled Piedmontese mountain towns like Chianale. (Photo: Edoardo Melchiori)

The logistical challenges of combining brain stimulation with cycling, we now realized, weren’t trivial. Geda had brought enough equipment from the clinic to zap two of us at once, but when you added in the time needed to clean electrodes between users and so on, it took about an hour for the three of us. A fully booked tour with eight cyclists would have been even more chaotic, even with extra staff and equipment. Bahrain Merida encountered similar challenges: it had sprung for ten sophisticated clinical-grade tDCS machines, each costing thousands of dollars, but it didn’t have enough trained medical staff to administer the treatment to everyone at once; instead, it only used one or two machines at a time.

Even though we’d come for the explicit purpose of trying out the brain stimulation, Trevor, John, and I couldn’t help grumbling a bit over the next few days. When the morning sun was shining and the mountains beckoned, it felt wrong to spend precious blue-skied hours fiddling with electrodes or to delay our dinner after a long day in the saddle. There were moments, as I waited patiently on van seats and in lobbies and hotel rooms across Piedmont and Savoy, when I began to question the basic premise of the trip. Sometimes I worried that the technology didn’t really work. Other times I worried that it did.


I’m all for e-bikes in the appropriate context. But it’s also obvious that it would be both unfair and meaningless to win a race using a motor, like winning a marathon by wearing roller skates. Even if the only person you’re competing with is yourself, you wouldn’t celebrate a new best time on your favorite training route (or, God forbid, a Strava KOM) if it was battery powered. Despite the Olympic motto, we intuitively understand that simply going faster (or higher or stronger) without any restrictions is not the fundamental goal of sport. Instead, there’s something else that’s harder to articulate—what the World Anti-Doping Agency (WADA) vaguely and unhelpfully refers to as “the spirit of sport.”

For nearly four decades, Thomas Murray, president emeritus of the Hastings Center bioethics research institute, has been trying to pin that elusive spirit down. A research grant from the National Science Foundation in 1979 started him down the path of trying to understand why athletes do or don’t choose to dope, which in turn led to the question of what sport is really about. His conclusion, laid out in academic papers and a 2018 book called Good Sport: Why Our Games Matter and How Doping Undermines Them, is that the highest goal of athletic competition is “the virtuous perfection of natural talents.” “Virtuous is a loaded word,” he acknowledged when I phoned to get his thoughts on brain stimulation. “Absolutely it is. But it’s the right word.”

In some situations, virtue is easy to discern. Training, nutrition, and coaching are all widely sanctioned methods of honing your abilities. Taking a crowbar to your main rival’s kneecap is not. But the distinction is often more nuanced. “There’s a golf ball that flies straighter, but sport bans it,” he points out. “They also bar certain clubs that make it easier to hit accurate shots out of the rough.” The point isn’t that all technology is bad; it’s that slicing into the rough should have a penalty. So the key question, whether you’re talking about drugs or technology, isn’t: Does it make you better? It’s: Does it change the things athletes have to do, and the qualities they have to possess, to win?

As the athletic implications of tDCS have become apparent, academics have started grappling with the ethical questions, variously arguing that it should be allowed, or that it should be banned, or even that athletes should be tested and handicapped to ensure that everyone gets exactly the same net benefit from it. The argument that caught my attention, from a 2013 paper on “neurodoping” by British neuroscientist and psychologist Nick Davis, was that brain stimulation “mediates a person’s ability but does not enhance it in the strictest sense.” You don’t get extra energy or stronger muscles from tDCS; you just find it a little easier to access the energy and strength that’s already present within you. Why would we ban something that simply helps us dig a little deeper?

The key question, whether you’re talking about drugs or technology, isn’t: Does it make you better? It’s: Does it change the things athletes have to do, and the qualities they have to possess, to win?

To me, though, that internal struggle to push a little closer to your limits is an essential part of endurance sport—in a sense, it’s the fundamental, defining characteristic. Change that and you change what it takes to win. After all, if you could just push a button to extract every ounce of power from your quads, what mystery would remain? Why would anyone watch—or participate?

I expected Murray, a long-standing defender of anti-doping orthodoxy, to share my qualms. But when I tried to pin him down about tDCS, he hedged. “The mere fact that something is a biomedical technology and enhances performance is not enough to disqualify it,” he said. “It’s only when it disrupts the connections between natural talents and their perfection.” That’s a judgment that may differ from sport to sport: a barefoot ultrarunner might have a different take on the appropriate role of technology in their sport compared to a gear-happy triathlete. WADA itself, according to spokesman James Fitzgerald, is aware of the controversy and has discussed it with experts in the field but hasn’t yet seen “compelling evidence” that it breaks the rules.

There is, however, one final caveat, Murray acknowledged before hanging up: “Once an effective technology gets adopted in a sport, it becomes tyrannical. You have to use it.” If the pros start brain-zapping, don’t kid yourself that it won’t trickle down to college, high school, and even the weekend warriors.


The queen stage of our tour, with almost 9,000 feet of climbing over two historic passes, started in the crenellated French mountain town of Briançon. In the breakfast room of our hotel, I chatted with Umberto, the tour guide who (to his mild chagrin) had been assigned to drive the support van instead of cycle with us. He comes from a prominent Piedmontese mountaineering family and had trained and worked as a mountain guide before switching to cycling. His affection for the Alpine landscape around us was reverent, almost poetic, and I got the sense that he sees the world much as Reinhold Messner does: where you end up is less important than how you get there. “When I was a kid growing up in the mountains,” he told me when I delicately probed his views on our tech-assisted adventure, “sport was about you. Your quest. But our society pushes everything to extremes.”

Those words echoed in my head as we rolled out under the radiant blue sky to tackle first the 7,400-foot Col d’Izoard and then the 9,000-foot Colle dell’Agnello, which Hannibal and his elephants supposedly crossed en route to Rome more than 2,000 years ago. A few miles from the summit of Agnello, I got confused about my gears. Tailing Massimo, as I had all week, suddenly seemed too slow to stay upright, so with a muttered apology, I moved past him and essentially launched an attack. By the time I realized that I’d accidentally been in my third gear rather than my lowest one, I was too sheepish to admit my mistake, so I decided to simply carry on to the summit and let it all hang out. As on Galibier, I was soon living from switchback to switchback, stretching the elastic thinner and thinner, and not at all sure that it wouldn’t snap before I reached the top.

An hour later, after a long, wobbly descent along endless switchbacks, past startled ibexes licking salt from the recently deiced roads, I coasted into the rustic town of Sampeyre, truly a spent force. There waiting for me in the hotel were Geda and a physical therapist from the IRR. Before I knew it, I was lying facedown on a massage table, having my deltoids kneaded as Geda hooked my brain up to the old familiar juice. It was an extremely pleasant way to end an epic day. I’d made it to the top of Agnello successfully—success being defined by the nebulous but utterly unfakeable sense that I’d pushed as hard as I was capable of and then a little bit more. Now the high-voltage massage would supercharge my recovery and, according to Pozzovivo, deepen my slumbers. “I have to say that, for me, the quality of sleep improved,” he claimed in a post-Giro interview last year.

I’d made it to the top of Agnello successfully—success being defined by the nebulous but utterly unfakeable sense that I’d pushed as hard as I was capable of and then a little bit more.

For the record, the idea that tDCS massage should aid recovery is “highly speculative,” according to Samuele Marcora, a University of Kent expert on the brain’s role in fatigue, who has studied tDCS and cycling. That’s probably being diplomatic. Even Geda acknowledged that the recovery protocol is mostly based on clinical experience rather than research. The pre-ride protocol is more plausible and well supported, Marcora told me. But even then, he added, “caffeine and a session with a good sport psychologist are likely to be much more useful.”

I knew and agreed with all this. Really, I did. But as the week wore on, I’d slowly realized that my ostensible reasons for going on the trip—investigating whether tDCS actually works, reflecting on the role technology should play in sport—were to some extent convenient covers for a more personal obsession. As much as I consider myself a skeptic and Luddite who runs and bikes with nothing but a grimy vintage Timex Ironman, I’ve been drawn in repeatedly by a fascination with brain stimulation. (Much to the annoyance, it turns out, of people like James Wrightson.) I’ve flown to Los Angeles for a zany Red Bull experiment with it, tried Halo Neuroscience’s headphones, written a whole book chapter about it, and now biked across the Alps on a bespoke brain stim tour.

As someone who has spent decades trying to figure out what the edge really feels like, the truth is that I’m as fascinated as I am horrified by the prospect of inching a little closer. If you pin me down, I’d say WADA should at least ban the technique in competition, even if, like stimulants and cannabis, it remains permitted in training. But I absolutely want to know with greater certainty whether it truly boosts endurance. Because if it does, that tells us something profound about the nature of our limits—that they’re in our neurons, not our muscle fibers. Maybe that’s what keeps drawing me back to the topic: the desire to find out if the edge I’ve been skirting all this time is just an illusion.

These are the riddles I was pondering when I finally flicked off my bedside lamp after my Herculean effort on Agnello and the subsequent massage. And for the first time since the trip began, I lay awake in the dark for nearly two hours, tossing and turning while my mind continued to race. Maybe it was because of the brain stimulation, or maybe it was despite it. Maybe it was the long day in the saddle, or the ill-advised third helping of gnocchi in butter, or the imponderable depth of the questions I was wrestling with. I’ll never know for sure—unless, as my history suggests is likely, I wire myself up again sometime.

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[ARTICLE] Transcranial Direct Current Stimulation to Facilitate Lower Limb Recovery Following Stroke: Current Evidence and Future Directions – Full Text HTML

Abstract

Stroke remains a global leading cause of disability. Novel treatment approaches are required to alleviate impairment and promote greater functional recovery. One potential candidate is transcranial direct current stimulation (tDCS), which is thought to non-invasively promote neuroplasticity within the human cortex by transiently altering the resting membrane potential of cortical neurons. To date, much work involving tDCS has focused on upper limb recovery following stroke. However, lower limb rehabilitation is important for regaining mobility, balance, and independence and could equally benefit from tDCS. The purpose of this review is to discuss tDCS as a technique to modulate brain activity and promote recovery of lower limb function following stroke. Preliminary evidence from both healthy adults and stroke survivors indicates that tDCS is a promising intervention to support recovery of lower limb function. Studies provide some indication of both behavioral and physiological changes in brain activity following tDCS. However, much work still remains to be performed to demonstrate the clinical potential of this neuromodulatory intervention. Future studies should consider treatment targets based on individual lesion characteristics, stage of recovery (acute vs. chronic), and residual white matter integrity while accounting for known determinants and biomarkers of tDCS response.

1. Introduction

Stroke is the second leading cause of death and third leading cause of adult disability globally [1]. With advancement in acute medical care, more people now survive stroke, but frequently require extensive rehabilitative therapy to reduce impairment and improve quality of life. For those that survive stroke, the damaging effects not only impact the individual and their family, but there is also increased burden on health unit resources and community services as the person leaves hospital, potentially requiring assistance to live in the community. Novel treatments that can enable restoration and enhance potential for stroke recovery are desperately needed and will have significant value for many aspects of stroke care.
True recovery from stroke impairment is underpinned by neuroplasticity. Neuroplasticity describes the brain’s ability to change in structure or function in order to help restore behavior following neural damage. Mechanisms of neuroplasticity are available throughout life but appear enhanced during critical periods of learning [2]. Across several animal studies, it has been shown that there is a period of heightened neuroplasticity that appears to open within several days following stroke [2,3,4] and correlates with rapid recovery [5]. In humans, the timing and duration of a similar critical period of heightened neuroplasticity are not clear, but it likely emerges early after stroke. Understanding the characteristics of a potential critical period of heightened neuroplasticity in humans is important for optimizing stroke rehabilitation and is the subject of current trials [6]. However, the importance of neuroplasticity for stroke recovery in humans is unequivocal, with imaging and physiological studies providing extensive evidence of brain changes correlating with improved behavior [7,8,9,10,11,12,13].
Transcranial direct current stimulation (tDCS) is a promising, non-invasive, method to induce neuroplasticity within the cerebral cortex and augment stroke recovery. Importantly, tDCS has potential to bidirectionally and selectively alter corticospinal excitability for up to one hour after stimulation [14,15]. Animal models indicate that tDCS modulates resting membrane potential, with anodal stimulation leading to neuronal depolarization and cathodal stimulation leading to neuronal hyperpolarization over large cortical populations [16]. Stimulation-induced changes may be potentiated by changes in intracellular calcium concentrations. For example, anodal tDCS applied to the surface of the rat sensorimotor cortex led to a rise in the intracellular calcium concentrations [17]. Local increases in calcium can result in short- and long-term changes in synaptic function [18]. In humans, pharmacological studies have also provided indirect evidence to suggest that tDCS after effects are mediated by changes in synaptic plasticity through mechanisms that resemble long-term potentiation (LTP) and long-term depression-like effects [19]. Oral administration of the NMDA-receptor antagonist dextromethorphan was found to suppress the post-tDCS effects of both anodal and cathodal stimulation, suggesting that tDCS after effects involve NMDA receptors [19]. Importantly, modulation of cortical activity with tDCS changes human behavior [20]. For example, in randomized sham-controlled trials, anodal stimulation of the motor cortex (M1) in the lesioned hemisphere was found to improve upper limb outcomes in chronic [21,22,23] and subacute stroke survivors [24,25,26], with behavior changes underpinned by increased cortical activity within the M1 [27]. Although much work remains to be performed regarding optimal stimulation doses, cortical targets and electrode montages, these studies provide some indication that tDCS may be beneficial in stroke recovery.
While there is indication that tDCS has potential to improve stroke recovery of the upper limb [28], there are comparatively fewer studies that have investigated tDCS for lower limb recovery after stroke. Lower limb rehabilitation is especially important, as the simple act of regaining the ability to walk has subsequent effects on the ability to engage in activities of daily living [29,30]. Furthermore, those receiving therapy targeting mobility have been shown to have reduced levels of depression and anxiety [31], which are important determinants of stroke recovery [32,33,34]. Therefore, novel interventions capable of enhancing lower limb recovery might improve not only lower limb motor performance but could have added benefit for stroke rehabilitation in general. The purpose of this review is to discuss tDCS as a technique to modulate brain activity and promote recovery of walking following stroke. Within this review, we will outline current studies that have investigated tDCS to improve lower limb motor performance in both healthy adults and people with stroke. Additionally, we propose a best-practice model of experimental design for lower limb tDCS to guide future application for lower limb stroke recovery.

2. Is it Possible to Modify Lower Limb Motor Networks with Transcranial Direct Current Stimulation?

One approach to modify activity of the lower limb motor network with tDCS is to target the M1, similar to studies involving the upper limb. However, targeted application with tDCS is challenging as, compared with upper limb representations, the lower limb M1 representations are more medial and deeper within the interhemispheric fissure (Figure 1). This presents two notable difficulties. First, the ability of targeted stimulation to the lower limb M1 within one hemisphere (e.g., the lesioned hemisphere in stroke) is challenging, as tDCS electrodes can be relatively large compared to the size of cortical representations, resulting in current spread that may inadvertently lead to stimulation within the opposite hemisphere. Second, the depth of the lower limb M1 representations may present a challenge to current penetration and depth with traditional tDCS applications. However, there is evidence to indicate that it is possible to modulate activity of the lower limb M1 with tDCS. Computational modelling has revealed that traditional anodal tDCS electrode montages (anode overlying the lower limb M1 and cathode overlying the contralateral orbit; Figure 1) can lead to the expected cortical excitability enhancement in the target cortex [35]. Indeed, reducing the size of the anode (3.5 cm × 1 cm) was found to improve the specificity of the current delivered to the cortex, while positioning the return electrode (cathode) to a more lateral position (T7/8 on the 10–10 EEG system) further improved current specificity, leading to greater changes in cortical excitability [35]. Experimental evidence also suggests that tDCS targeting the lower limb M1 can modify excitability. Jeffrey and colleagues [36] utilized an anodal-tDCS montage (2 mA, 10 min) over the lower limb M1 and found that motor-evoked potentials (MEPs) of the tibialis anterior muscle increased by as much as 59% compared to sham conditions. Along similar lines, 10 sessions of anodal tDCS (2 mA, 10 min) targeting the lower limb M1 was found to increase the amplitude of MEPs recorded from the paretic tibialis anterior compared to sham stimulation [37]. This empirical evidence provides some support to the computational modelling to suggest that the use of tDCS targeting the lower limb M1 can modify corticospinal excitability.
Although M1 has received attention as a stimulation target to modify excitability of the lower limb M1, there is potential for cerebellar tDCS to induce similar, or possibly more prominent, behavioral and neurophysiological changes. It is noteworthy that a computational modelling study that compared electrode montages targeting M1 and the cerebellum found that cerebellar stimulation produced substantially higher electric field strengths in the target area compared to M1 stimulation, suggesting the cerebellum may indeed be a suitable target for tDCS [38]. Behaviorally, the cerebellum contributes to motor planning, learning, and control; this influence is in part mediated by connections to M1 via the cerebellothalamocortical tracts, previously reported to play a key role in motor skill learning in mice [39]. Although this stimulation technique has received comparatively little attention compared to M1 stimulation, there is some indication that it is possible to modify cerebellar excitability in a focal and polarity specific manner [40]. Whether cerebellar tDCS is required to modify excitability of M1 for behavioral change is unclear. However, if a desired outcome was to modify M1 excitability with cerebellar stimulation, a pertinent challenge would be whether cerebellar tDCS can achieve the specificity required to precisely target the lower limb M1 in one hemisphere. Although speculative, one approach could be to pre-activate M1 through a contralateral lower limb motor task in order to bias the effects of tDCS towards those networks activated to perform the task. In support, there is some evidence in the upper limb that performance of a task during cerebellar tDCS does interact with the change in M1 excitability [41].[…]

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[Abstract + References] Perspectives: Hemianopia—Toward Novel Treatment Options Based on Oscillatory Activity?

Stroke has become one of the main causes of visual impairment, with more than 15 million incidences of first-time strokes, per year, worldwide. One-third of stroke survivors exhibit visual impairment, and most of them will not fully recover. Some recovery is possible, but this usually happens in the first few weeks after a stroke.

Most of the rehabilitation options that are offered to patients are compensatory, such as optical aids or eye training. However, these techniques do not seem to provide a sufficient amount of improvement transferable to everyday life.

Based on the relatively recent idea that the visual system can actually recover from a chronic lesion, visual retraining protocols have emerged, sometimes even in combination with noninvasive brain stimulation (NIBS), to further boost plastic changes in the residual visual tracts and network.

The present article reviews the underlying mechanisms supporting visual retraining and describes the first clinical trials that applied NIBS combined with visual retraining. As a further perspective, it gathers the scientific evidence demonstrating the relevance of interregional functional synchronization of brain networks for visual field recovery, especially the causal role of α and γ oscillations in parieto-occipital regions.

Because transcranial alternating current stimulation (tACS) can induce frequency-specific entrainment and modulate spike timing–dependent plasticity, we present a new promising interventional approach, consisting of applying physiologically motivated tACS protocols based on multifocal cross-frequency brain stimulation of the visuoattentional network for visual field recovery.

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[WEB PAGE] Upper arm rehabilitation after severe stroke: where are we? – Physics World

10 Sep 2019 Andrea Rampin 
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Stroke is the second leading cause of death worldwide and the third cause of induced disability, according to estimates from the Global Burden of Diseases, Injuries, and Risk Factors Study. Treatments based on constraint-induced movement therapy, occupational practice, virtual reality and brain stimulation can work well for patients with mild impairment of upper limb movement, but they are not as effective for those burdened by severe disability. Therefore, novel individualized approaches are needed for this patient group.

Martina Coscia from the Wyss Center for Bio and Neuroengineering in Geneva, and colleagues from several other Swiss institutes, have published a review paper summarizing the most advanced techniques in use today for treatment of severe, chronic stroke patients. The researchers describe techniques being developed for upper limb motor rehabilitation: from robotics and muscular electrical stimulation, to brain stimulation and brain–computer/machine interfaces (Brain 10.1093/brain/awz181).

Robot-aided rehabilitation approaches include movement-assisting exoskeletons and end-effector devices, which enable upper arm movement by stimulating the peripheral nervous system. These techniques can also trigger reorganization of the impaired peripheral nervous system and encourage rehabilitation of the damaged somatosensory system. Several studies have reported the efficiency of robot-aided rehabilitation, alone or in combination with other techniques, in the treatment of upper limb motor impairment. One study that included severely impaired individuals also demonstrated encouraging results.

Muscular electrical stimulation can help improve the connection of motor neurons to the spinal cord and the motor cortex. Researchers have also demonstrated that application of electrical stimuli to the muscles provides positive effects on the neurons responsible for sensory signal transduction to the brain, thereby improving the motion control loop function. By modulating motor neurons’ sensitivity, muscular electrical stimulation inhibits the muscle spasms observed in other treatments.

More recently, therapies have moved on from the simple use of currents to harnessing coordinated stimuli to orchestrate more complex, task-related movements. Although this particular set of techniques didn’t show a particular advantage over physiotherapy in long-term studies of patients with mild upper limb impairment, it did seem to have a stronger effect for chronic severe patients.

Stimulating the brain

Brain stimulation, meanwhile, stimulates cortical neurons in order to improve their ability to form new connections within the affected neural network. Brain stimulation techniques can be divided into two branches – electrical and magnetic – both of which can activate or inhibit neural activity, depending on the polarity and intensity of the stimulus.

Transcranial magnetic stimulation

Researchers have achieved encouraging results using both techniques. In particular, magnetic field-triggered inhibition of the contralesional hemisphere (the hemisphere that was not affected by the stroke) activity yielded positive results. Magnetic, low-frequency stimulation of the contralesional hemisphere also proved encouraging – improving the reach to grasp ability of patients, although only for small objects. Excitingly, some studies suggest that coupling contralesional cortex inhibition with magnetic stimulation of the chronically affected area could achieve effective results.

Within these techniques, one promising approach is invasive brain stimulation, in which a device is surgically implanted in a superficial region of the brain. Such techniques allow for more sustained and spatially-oriented stimulation of the desired brain regions. The Everest trial used such methods and showed significant improvement for a larger percentage of patients after 24 weeks, compared with standard rehabilitation protocols.

Another promising recent development is non-invasive deep-brain stimulation, achieved by temporally interfering electric fields. The authors envision that a deeper understanding of the complex mechanisms involved in the brain’s reactions to magnetic and electrical stimulation will provide an important assistance in clinical application of these techniques.

The final category, brain–computer or brain–machine interfaces (BCIs or BMIs), exploit electroencephalogram (EEG) patterns to trigger feedback or an action output from an external device. Devices that produce feedback are used to train the patient to recruit the correct zone of the brain and help reorganize its interconnections. These techniques have only recently transitioned to the clinic; however, early results and observations are promising. For example, a BCI technique coupled with muscular electrical stimulation restored patients’ ability to extend their fingers.

In recent years, researchers have also tested combinations of the techniques described above. For example, combinations of robotics and muscular electrical stimulation have shown encouraging results, especially when more than one articulation was targeted by the treatment. Combining brain stimulation with muscular electrical stimulation and robotics has proved more effective in severe than in moderate cases. Also, coupling of muscular electrical stimulation with magnetic inhibitory brain stimulation provided better results than either individual technique. Interestingly, addition of electrical brain stimulation to a BCI system coupled with a robotic motor feedback enhanced the outcome, helping to achieve adaptive brain remodelling at the expense of inappropriate reorganization.

Coscia and co-authors highlight that all the techniques studied share a range of limitations that should be addressed, such as small sample size, limited understanding of the underlying mechanisms, lack of treatment personalization and minimal attention to the training task, which they note is often of limited importance for daily life. Addressing these limitations might be key to improving the clinical outcome for patients with severe stroke-induced upper limb paralysis treated with neurotechnology-aided interventions. Moreover, the authors plan to begin a clinical trial to test the use of a novel personalized therapy approach that will include a combination of the described techniques.

 

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[WEB SITE] What is neurohacking and can it actually rewire your brain?

Marc Bordons / Stocksy

What is neurohacking and can it actually rewire your brain?

Although at one point, “hack” referred to a creative solution to a tech problem, the term can apply to pretty much anything now. There are kitchen hacks, productivity hacks, personal finance hacks. Brain hacks, or neurohacks, are among the buzziest, though, thanks largely to the Silicon Valley techies who often swear by them as a way to boost their cognitive function, focus, and creativity. Mic asked a neuroscientist to explain neurohacking, which neurohacking methods are especially promising, which are mostly hype, and how to make neurohacking work for you.

First things first: Neurohacking, is a broad umbrella term that encompasses anything that involves “manipulating brain function or structure to improve one’s experience of the world,” says neuroscientist Don Vaughn of Santa Clara University and the University of California, Los Angeles. Like the other myriad forms of hacking, neurohacking uses an engineering approach, treating the brain as a piece of hardware that can be systematically modified and upgraded.

Neurohacking techniques can fall under a number of categories — here are a few of the most relevant ones, as well as the thinking behind them.

Brain stimulation

This involves applying an electric or magnetic field to certain regions of the brain in non-neurotypical people to make their activity more closely resemble that seen in a neurotypical brain. In 2008, the Food and Drug Administration approved transcranial magnetic stimulation (TMS) — a noninvasive form of brain stimulation which delivers magnetic pulses to the brain in a noninvasive manner — for major depression. Since then, the FDA has also approved TMS for pain associated with migraines with auras, as well as obsessive-compulsive disorder. Established brain stimulation techniques (such as TMS or electroconvulsive therapy) performed by an expert provider, such as a psychiatrist or neuroscientist, are generally safe, Vaughn says.

Neurofeedback

This one involves using a device that measures brain activity, such as an electroencephalogram (EEG) or a functional magnetic resonance imaging (fMRI) machine. People with neuropsychological disorders receive feedback on their own brain activity — often in the form of images or sound — and focus on trying to make it more closely resemble the brain activity in a healthy person, Vaughn says. This could happen through changing their thought patterns, Vaughn says. Another possibility is that the feedback itself, or the person’s thoughts about the feedback, may somehow lead to a change in their brain’s wiring.

Reducing cognitive load

This means minimizing how much apps, devices, and other tech compete for your attention. Doing so can sharpen and sustain your focus, or what Vaughn refers to as your attention quotient (AQ). To boost his AQ, Vaughn listens to brown noise, which he likens to “white noise, but deeper.” (Think the low rush of a waterfall versus pure static.) He also chews gum, which he says provides an outlet for his restless “monkey mind” while still allowing him to focus on the task at hand.

Reducing cognitive load can also deepen your connection with others. Vaughn uses Voicea, an app based on an AI assistant that takes and store notes of meetings, whether over the phone or in-person, allowing him to focus solely on the conversation, not on recording it. “If we can quell those disruptions that occur because of the way work is done these days, it will allow us to focus and be more empathic with each other,” he says.

Monitoring sleep

Tracking your sleep patterns and adjusting them accordingly. Every night, you go through around five or so stages of sleep, each one deeper than the last. “People are less groggy and make fewer errors when they wake up in a lighter stage of sleep,” Vaughn says. He uses Sleep Cycle, an app that tracks your sleep patterns based on your movements in bed to rouse you during your lightest sleep stage.

Andrey Popov / Shutterstock

Microdosing

Microdosing is the routinely consumption of teensy doses of psychedelics like LSD, ecstasy, or magic mushrooms. Many who practice microdosing follow the regimen recommended by James Fadiman, psychologist and author of The Psychedelic Explorer’s Guide: Safe, Therapeutic, and Sacred Journeys: a twentieth to a tenth of a regular dose, once every three days for about a month. While a regular dose may make you trip, a microdose has subtler effects, with some users reporting, for instance, enhanced energy and focus, per The Cut.

Nootropics

These are OTC supplements or drugs taken to enhance cognitive function. They range from everyday caffeine and vitamin B12 (B12 deficiency has been associated with cognitive decline) to prescription drugs like Ritalin and Adderall, used to treat ADHD and narcolepsy, as well as Provigil (modafinil), used to treat extreme drowsiness resulting from narcolepsy and other sleep disorder. (All three of these drugs promote wakefulness.) The science behind nootropic supplements in particular remains rather murky, though.

Does neurohacking work, though?

Vaughn finds microdosing, neurostimulation, and neurofeedback especially promising for neuropsychological disorders. Although studies suggest that larger doses of psychedelics could help with disorders such as PTSD and treatment-resistant major depression, there are few studies on microdosing psychedelics. “The little science that has been done…is mixed—perhaps slightly positive,” Vaughn says. “Microdosing is promising mainly because of anecdotal evidence.” Meanwhile, neurostimulation can be used noninvasively in some cases, and TMS has already received FDA approval for a handful of conditions. Neurofeedback is not only non-invasive, but offers immediate feedback, and studies suggest it could be effective for PTSD and addiction.

But it’s important to note that just because these methods could positively alter brain function in people with neuropsychological disorders, that “doesn’t mean it’s going to take a normal system and make it superhuman,” Vaughn says. “I think there are lots of small hacks to be done that could add up to something big,” rather than huge hacks that can vastly upgrade cognitive function, a la Limitless. Thanks to millions of years of evolution, the human brain is already pretty damn optimized. “I just don’t know how much more we can tweak it to make it better,” Vaughn says.

As far as enhancements for neurotypical brains, he says that “you’ll probably see a much greater improvement” from removing distractions in your environment to reduce cognitive load than say, increasing your B12 intake — which brings us to an important disclaimer about nootropic supplements in particular. As with all supplements, they aren’t FDA-regulated, meaning that companies that sell them don’t need to provide evidence that they’re safe or effective. Vaughn recommends trying nootropics that research has shown to be safe and effective, like B12 or caffeine.

How can I start neurohacking?

As tempting as it is, adopting every neurohack under the sun is “not the answer,” Vaughn says. Remember, everyone is different. While your best friend may gush about how much her mood has improved since she began microdosing shrooms, your brain might not respond to microdosing—or maybe taking psychedelics just doesn’t align with your ethics.

Start by exploring different neurohacks, and of course, be skeptical of any product that makes outrageous claims. Since neurofeedback isn’t a common medical treatment, talk to your doctor about enrolling in academic studies on neurofeedback, or companies that offer it if you’re interested, Vaughn says. You should also talk to your doctor if you want to try brain stimulation. A doctor can prescribe you Adderall, Ritalin, or Provigil but only for their indicated medical uses, not for cognitive enhancement.

Ultimately, neurohacks are tools, Vaughn says. “You have to find the one that works for you.” If anything, taking this DIY approach to improving your brain function will leave you feeling empowered, a benefit that probably rivals anything a supplement or sleep tracking app could offer.

 

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[WEB PAGE] The Use of Noninvasive Brain Stimulation, Specifically Transcranial Direct Current Stimulation After Stroke

Motor impairment is a leading cause of disability after stroke. Approaches such as noninvasive brain stimulation are being investigated to attempt to increase effectiveness of stroke rehabilitation interventions. There are several types of noninvasive brain stimulation: repetitive transcranial magnetic stimulation, transcranial direct stimulation (tDCS), transcranial alternative current stimulation, and transcranial pulsed ultrasound to name a few. Of the types of noninvasive brain stimulation, repetitive transcranial magnetic stimulation and tDCS have been most extensively tested to modulate brain activity and potentially behavior. These two techniques have distinctive modes of action. Repetitive transcranial magnetic stimulation directly stimulates neurons in the brain and, given the appropriate conditions, leads to new action potentials. On the other hand, tDCS polarizes neuronal tissue including neurons and glia modulating ongoing firing patterns. There are also differences in cost, utility, and knowledge skill required to apply tDCS and repetitive transcranial magnetic stimulation. Transcranial direct stimulation is relatively inexpensive, easy to administer, portable, and may be applied while undergoing therapy, with lasting excitability changes detectable up to 90 minutes after administration. Repetitive transcranial magnetic stimulation equipment is bulkier, expensive, technically more challenging, and a patient’s head must remain still when treatment is being applied therefore needs to be administered before or after a session of rehabilitation. Because of these differences, tDCS has been more accessible and has rapidly grew as a potential tool to be used in neurorehabilitation to facilitate retraining of activities of daily living (ADL) capacity and possibly to improve restoration of neurological function after stroke.

There are three current stimulation approaches using tDCS to modulate corticomotor regions after stroke. In anodal stimulation mode, the anode electrode is placed over the lesioned brain area and a reference electrode is applied over the contralateral orbitofrontal cortex. Anodal tDCS is placed over the ipsilesional hemisphere to improve the responses of perilesional areas to training protocols. In cathodal stimulation, the cathode electrode is placed over the nonlesioned brain area and reference electrode over the contralateral (ipsilesional) orbitofrontal cortex. This approach has been predicated on the hypothesis that the nonstroke hemisphere will be inhibited by tDCS resulting in an increased activation of the ipsilesional hemisphere due to rebalancing of a presumably abnormal interhemispheric interaction. Although some studies have shown this approach to be beneficial, the causative role of interhemispheric interaction imbalance has been recently challenged and refuted.1 Thus, if cathodal stimulation approaches are beneficial, the behavioral effect cannot be explained by a presumed correction of abnormal interhemispheric connectivity. Finally, dual tDCS approach involves simultaneous application of the anode over the ipsilesional and the cathode over the contralesional side. Here again, the intended mechanism of action is to rebalance the presumably abnormal interhemispheric interaction.

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CLINICAL QUESTIONS ADDRESSED

What is the best tDCS type and electrical configuration? What are the effects of tDCS with rehabilitation program for upper limb recovery after stroke?

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RESEARCH FINDINGS OF tDCS

This short article discusses data obtained from a network meta-analysis of randomized controlled trials and a recent meta-analysis. The network meta-analysis included 12 randomized controlled trials including 284 participants examining the effect of tDCS on ADL function in the acute, subacute, and chronic phases after stroke.2 The meta-analysis included 9 studies with 371 participants in any stage after stroke.3

The network meta-analysis found evidence of a significant moderate effect in favor of cathodal tDCS without significant effects of dual tDCS, anodal tDCS, or sham tDCS. There was no difference in safety (as assessed by dropouts and adverse events) between sham tDCS, physical rehabilitation, cathodal tDCS, dual tDCS, and anodal tDCS. Elsner in a previous review of tDCS in 2016 found an effect on improving ADL, as well as function of the arm and lower limb, muscle strength, and cognition. Thus, the findings from the most recent meta-analysis indicating cathodal that tDCS improves ADL capacity are in line with previous meta-analyses. Of note, there was no evidence of an effect of either cathodal or other tDCS stimulation approaches on upper paretic limb impairment after stroke as measured by the Fugl-Meyer scale.

A meta-analysis that included participants in any stage after the stroke showed that tDCS in conjunction with multiple sessions of rehabilitation had no significant effect over delivering therapy alone for upper limb impairment and activity after stroke. This negative finding might be due to patient’s being in an acute, subacute, or chronic stage after stroke as well as variations in the type of therapy performed paired with tDCS (ie, conventional vs. constraint-induced movement therapy vs. robot protocol).

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RECOMMENDATIONS FOR PHYSIATRIC PRACTICE

There seems to be a modest effect supporting the use of tDCS as a co-adjuvant of rehabilitation interventions to improve ADLs after stroke. Cathodal tDCS seems to be the most promising approach, especially when applied early after the stroke. However, the evidence remains preliminary and does not warrant a widespread change in clinical rehabilitation practice at this time.

There is no evidence supporting the use of tDCS to improve motor impairment (as measured by the FMS) at this point.

Importantly, tDCS remains as a very safe intervention, with no differences in safety when real vs. control tDCS is applied.

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REFERENCES

1. Xu J, Branscheidt M, Schambra H, et al: Rethinking interhemispheric imbalance as a target for stroke neurorehabilitation. Ann Neurol 2019;85:502–13

2. Elsner B, Kwakkel G, Kugler J, et al: Transcranial direct current stimulation (tDCS) for improving capacity in activities and arm function after stroke: a network meta-analysis of randomised controlled trials. J Neuroeng Rehabil 2017;14:

3. Tedesco Triccas L, Burridge J, Hughes A, et al: Multiple sessions of transcranial direct current stimulation and upper extremity rehabilitation in stroke: a review and meta-analysis. Clin Neurophysiol2016;127:946–55

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[ARTICLE] Neurotechnology-aided interventions for upper limb motor rehabilitation in severe chronic stroke – Full Text

Abstract

Upper limb motor deficits in severe stroke survivors often remain unresolved over extended time periods. Novel neurotechnologies have the potential to significantly support upper limb motor restoration in severely impaired stroke individuals. Here, we review recent controlled clinical studies and reviews focusing on the mechanisms of action and effectiveness of single and combined technology-aided interventions for upper limb motor rehabilitation after stroke, including robotics, muscular electrical stimulation, brain stimulation and brain computer/machine interfaces. We aim at identifying possible guidance for the optimal use of these new technologies to enhance upper limb motor recovery especially in severe chronic stroke patients. We found that the current literature does not provide enough evidence to support strict guidelines, because of the variability of the procedures for each intervention and of the heterogeneity of the stroke population. The present results confirm that neurotechnology-aided upper limb rehabilitation is promising for severe chronic stroke patients, but the combination of interventions often lacks understanding of single intervention mechanisms of action, which may not reflect the summation of single intervention’s effectiveness. Stroke rehabilitation is a long and complex process, and one single intervention administrated in a short time interval cannot have a large impact for motor recovery, especially in severely impaired patients. To design personalized interventions combining or proposing different interventions in sequence, it is necessary to have an excellent understanding of the mechanisms determining the effectiveness of a single treatment in this heterogeneous population of stroke patients. We encourage the identification of objective biomarkers for stroke recovery for patients’ stratification and to tailor treatments. Furthermore, the advantage of longitudinal personalized trial designs compared to classical double-blind placebo-controlled clinical trials as the basis for precise personalized stroke rehabilitation medicine is discussed. Finally, we also promote the necessary conceptual change from ‘one-suits-all’ treatments within in-patient clinical rehabilitation set-ups towards personalized home-based treatment strategies, by adopting novel technologies merging rehabilitation and motor assistance, including implantable ones.

Introduction

Stroke constitutes a major public health problem affecting millions of people worldwide with considerable impacts on socio-economics and health-related costs. It is the second cause of death (Langhorne et al., 2011), and the third cause of disability-adjusted life-years worldwide (Feigin et al., 2014): ∼8.2 million people were affected by stroke in Europe in 2010, with a total cost of ∼€64 billion per year (Olesen et al., 2012). Due to ageing societies, these numbers might still rise, estimated to increase 1.5–2-fold from 2010 to 2030 (Feigin et al., 2014).

Improving upper limb functioning is a major therapeutic target in stroke rehabilitation (Pollock et al., 2014Veerbeek et al., 2017) to maximize patients’ functional recovery and reduce long-term disability (Nichols-Larsen et al., 2005Veerbeek et al., 2011Pollock et al., 2014). Motor impairment of the upper limb occurs in 73–88% first time stroke survivors and in 55–75% of chronic stroke patients (Lawrence et al., 2001). Constraint-induced movement therapy (CIMT), but also standard occupational practice, virtual reality and brain stimulation-based interventions for sensory and motor impairments show positive rehabilitative effects in mildly and moderately impaired stroke victims (Pollock et al., 2014Raffin and Hummel, 2018). However, stroke survivors with severe motor deficits are often excluded from these therapeutic approaches as their deficit does not allow easily rehabilitative motor training (e.g. CIMT), treatment effects are negligible and recovery unpredictable (Byblow et al., 2015Wuwei et al., 2015Buch et al., 2016Guggisberg et al., 2017).

Recent neurotechnology-supported interventions offer the opportunity to deliver high-intensity motor training to stroke victims with severe motor impairments (Sivan et al., 2011). Robotics, muscular electrical stimulation, brain stimulation, brain computer/machine interfaces (BCI/BMI) can support upper limb motor restoration including hand and arm movements and induce neuro-plastic changes within the motor network (Mrachacz-Kersting et al., 2016Biasiucci et al., 2018).

The main hurdle for an improvement of the status quo of stroke rehabilitation is the fragmentary knowledge about the physiological, psychological and social mechanisms, their interplay and how they impact on functional brain reorganization and stroke recovery. Positive stimulating and negatively blocking adaptive brain reorganization factors are insufficiently characterized except from some more or less trivial determinants, such as number and time of treatment sessions, pointing towards the more the better (Kwakkel et al., 1997). Even the long accepted model of detrimental interhemispheric inhibition of the overactive contralesional brain hemisphere on the ipsilesional hemisphere is based on an oversimplification and lack of differential knowledge and is thus called into question (Hummel et al., 2008Krakauer and Carmichael, 2017Morishita and Hummel, 2017).

Here, we take a pragmatic approach of comparing effectiveness data, keeping this lack of knowledge of mechanisms in mind and providing novel ideas towards precision medicine-based approaches to individually tailor treatments to the characteristics and needs of the individual patient with severe chronic stroke to maximize rehabilitative outcome.[…]

Continue —>   Neurotechnology-aided interventions for upper limb motor rehabilitation in severe chronic stroke | Brain | Oxford Academic

Conceptualization of longitudinal personalized rehabilitation-treatment designs for patients with severe chronic stroke. Ideally, each patient with severe chronic stroke with a stable motor recovery could be stratified based on objective biomarkers of stroke recovery in order to select the most appropriate/promising neurotechnology-aided interventions and/or their combination for the specific case. Then, these interventions can be administered in the clinic and/or at home in sequence, moving from one to another only when patient’s motor recovery plateaus. In this way, comparisons of the efficacy of each intervention (grey arrows) are still possible, and if the selected interventions and/or their combination are suitable, motor recovery could increase.

Conceptualization of longitudinal personalized rehabilitation-treatment designs for patients with severe chronic stroke. Ideally, each patient with severe chronic stroke with a stable motor recovery could be stratified based on objective biomarkers of stroke recovery in order to select the most appropriate/promising neurotechnology-aided interventions and/or their combination for the specific case. Then, these interventions can be administered in the clinic and/or at home in sequence, moving from one to another only when patient’s motor recovery plateaus. In this way, comparisons of the efficacy of each intervention (grey arrows) are still possible, and if the selected interventions and/or their combination are suitable, motor recovery could increase.

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