Posts Tagged Transcranial Direct Current Stimulation

[ARTICLE] A review of transcranial electrical stimulation methods in stroke rehabilitation – Full Text

 

Abstract

Transcranial electrical stimulation (TES) uses direct or alternating current to non-invasively stimulate the brain. Neuronal activity in the brain is modulated by the electrical field according to the polarity of the current being applied. TES includes transcranial direct current stimulation (tDCS), transcranial random noise stimulation, and transcranial alternating current stimulation (tACS). tDCS and tACS are the two non-invasive brain stimulation techniques that have been used alone or in combination with other rehabilitative therapies for the improvement of motor control in hemiparesis. Increasing research in these methods is being carried out to improvise on the existing technology because they have proven to exhibit a lasting effect, thereby contributing to brain plasticity and motor re-learning. Artificial stimulation of the lesioned or non-lesioned hemisphere induces participation of its cells when a movement is being performed. The devices are portable, stimulation is easy to deliver, and they are not known to cause any major side effects which are the foremost reasons for their trials in stroke rehabilitation. Recent research is focused on maximizing the outcome of stroke rehabilitation by combining them with other modalities. This review focuses on stimulation protocols, parameters, and the results obtained by these techniques and their combinations.

Key Message: Motor recovery and control poses a great challenge in stroke rehabilitation. Transcranial electrical stimulation methods look promising in this regard as they have been shown to augment long-term and short-term potentiation in the brain which may have a role in motor re-learning. This review discusses transcranial direct current stimulation and transcranial alternating current stimulation in stroke rehabilitation.

According to World Health Organization (WHO) statistics on 2016, cardiovascular diseases (CVD) are the foremost cause of death and adult disability worldwide.[1],[2] Stroke statistics in India show that the incidence of stroke was 435/100,000 population and only one in three stroke survivors are hospitalized and given further rehabilitation because treatment is expensive.[3]

Stroke survivors are faced with paralysis of one side of the body, that is, the side contra-lateral to the affected side in the brain. Rehabilitation aims at strengthening these muscles to prevent wastage and bring back function to the maximum possible extent. Taking the upper extremity into consideration, a combination of muscle over-activity (spastic muscle) in certain groups and weakening in other groups causes poor motor control leading to deformities and inability to reach, grasp, and release objects.

Various therapies such as splinting, stretching exercises, functional electrical stimulation (FES), and mirror therapy are being used to treat this condition, with varying degrees of success. In an ideal situation, the aim of stroke rehabilitation is to recover the paralyzed limb to an extent that it is functionally useful. In this context, recent research is being conducted in neuroplasticity or motor-relearning. Neuroplasticity refers to the brain being able to adapt to changes in response to its external environment and stimulation. TES and transcranial magnetic stimulation (TMS) are the non-invasive brain stimulation (NIBS) methods that invoke this type of re-learning.[4],[5]

NIBS methods include TMS and TES since they non-invasively stimulate the cortex. These methods are still under research for medical applications and were first introduced to treat psychiatric conditions such as insomnia, chronic anxiety, mild depression and post stroke aphasia.[6],[7],[8] Recently, tDCS has also been tried on normal individuals and was shown to improve cognition, working memory, and performance.[9],[10],[11] These methods are now gaining importance in stroke rehabilitation because they provide motor relearning probably through cortical reorganization, which occurs because the neural continuity between the brain and the periphery is intact.[12]

This article attempts to review the stimulation protocols used for TES by various research groups and the results obtained. The first section begins with an introduction to non-invasive methods of brain stimulation followed by a brief summary on the history that led to the use of TES for stroke rehabilitation. Later sections deal with tDCS and tACS. The section on tDCS is further subdivided into tDCS alone and tDCS with adjuvant therapy. The tables give a list of the studies that have been carried out for neurorehabilitation, although it is not meant to be an exhaustive list.[…]

Continue —> A review of transcranial electrical stimulation methods in stroke rehabilitation Solomons CD, Shanmugasundaram V Neurol India

Figure 1: Placement of electrodes for a-tDCS and c-tDCS

Figure 1: Placement of electrodes for a-tDCS and c-tDCS

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[OPINION ARTICLE] The Two-Fold Ethical Challenge in the Use of Neural Electrical Modulation – Full Text

  • Centro Universitario Internazionale, Arezzo, Italy

The use of electrical stimulation to influence biological functions and/or pathological processes in the body has been recently termed “electroceuticals.” The most commonly used techniques are “neural electroceuticals,” forms of electrical modulation of the brain that seem to represent the new frontier both to treat neurological and psychiatric diseases, when no other effective treatments are available, and to enhance cognitive functions (Kambouris et al., 2014Reardon, 2014;Miller and Matharu, 2017).

These types of medical interventions have given rise to a wide ethical debate (Pickersgill and Hogle, 2015Lavazza and Colzato, 2018Packer et al., 2018). Here I wish to introduce two new challenges bearing important moral implications, which require the careful consideration of the scientific and philosophical community. These challenges can be co-present and can be placed in the same framework of human augmentation and the willingness to go beyond one’s own physiological limits. However, it is possible to analytically distinguish them according to their initial conditions and their different scopes, as it will be explained.

The first challenge concerns a possible shift from a mainly therapeutic use of electroceuticals to a use aimed at enhancement. This potential shift is due to the fact that technology has now fulfilled a very ancient human aspiration, that of overcoming one’s limits and improving indefinitely. And the effect of this shift could be a segmentation of society between enhanced and non-enhanced individuals, something that goes against the essentially egalitarian project of modern thought (Rawls, 1999Mason, 2006).

The second challenge concerns the aging tendency and the demographic contraction that characterize European countries and Japan, and which may soon affect other economically developed countries (Lutz et al., 2008Długosz, 2011Murray et al., 2018). This trend, over time, will reduce the overall availability of cognitive skills and abilities in those populations, who will have to manage increasingly complex and diversified societies and environments. This mismatch between the needs arising from one’s life context and the available resources could push people to resort to electroceuticals as means of strengthening their cognitive abilities, opening up scenarios in which ethical evaluations will have a role to play. Below, I will address these two challenges, giving more space to the first.

Going Beyond One’s Limits

Ever since the Odyssey, humans have always desired to alter their minds in a controlled manner through a mix of substances and to go beyond the limits established by brain physiology (Koops et al., 2013). In recent decades, important steps have been taken in this direction, both with new molecules able to act on brain chemistry and with instruments capable of electrically modulating brain activity (Dresler et al., 2018). Scientific consensus on the cognitive enhancement potential of the so-called Non-Invasive Brain Stimulation (NIBS) is not yet unanimous (see Horvath et al., 2015 on one side; Price and Hamilton, 2015 on the other side), but it is undeniable that there is a great investment in research. A growing amount of research studies have produced at least some results in the field, even with different effects at an inter- and intra-individual level. For example, Transcranial Direct Current Stimulation (tDCS) is a form of neurostimulation that so far has been used on healthy subjects to enhance mathematical cognition, reading, memory, mood, learning, perception, decision making, creativity motivation, and moral reasoning (Chi and Snyder, 2012Callaway, 2013Meinzer et al., 2013Snowball et al., 2013Parkin et al., 2015). The use of NIBS is very often deemed effective by the public due to wide media coverage and Internet ads (Fitz and Reiner, 2015). However, the road to enhancement is now open and more relevant and consistent results may come both from more in-depth knowledge on the functioning of the nervous system and from more performing devices.

What are the consequences of a greater concentration of medical-scientific skills and resources in the field of cognitive neuroenhancement? Medicine is changing, suggests Harari (2016, ch 9), whose line of reasoning is useful here, even though he does not refer to electroceuticals. Somewhat oversimplifying, it can be said that the vocation of medicine, for most of its history, has been to treat the sick, to restore to a better condition those who saw their health deteriorate or were born with a congenital pathology or deficit. Classical Hippocratic medicine has then recently introduced the idea of disease prevention and the notion of combating the symptoms of aging (Bynum, 2008). This was a conceptual and clinical turning point, which has opened the door to the idea of improving the physical and cognitive status of healthy people, thus fulfilling the human aspiration I mentioned earlier, which had not yet been reflected in medical practice.

From an ethical point of view, caring for the sick—at least in principle—is an egalitarian project, because it envisions a level of health which each person can and should ideally reach, despite the limits of medical knowledge and of material resources. This project goes hand in hand with—and derives from—the social and political idea that Christianity and the Enlightenment have brought onto the Western world, according to which all human beings have equal dignity and rights and deserve the same treatment (despite the many exceptions due to material contingencies and the organization of life in society) (Hunt, 2007).

As Harari emphasizes, enhancing those in good health might instead be an elitist project, because it necessarily ignores universal levels of functioning or performance that are applicable to all (More and Vita-More, 2013). Every individual legitimately seeks to gain an advantage over others by exploiting the means made available by medical research to those who can pay for them. Once a certain level of enhancement has been achieved by the whole—or at least by the majority—of the population, the given technology will be available to everyone in terms of both diffusion and cost, and there will be demand for new and further forms of enhancement. These forms of enhancement will be sought by medical-scientific research within the dynamic that always pushes further the frontier of technical knowledge.

Harari’s prediction is that the poorest people in the next 50 years will have much better healthcare than today, whereas the health inequality measured in functioning and physical-cognitive performance might get much worse. Strong inequalities have always been present in the history of mankind, even when enhancement was not even contemplated as a possibility. However, for reasons related to technical progress, today there may be no shared interest in ensuring healthcare to the entire population according to the best current standards.

In the twentieth century many states had an interest in, and the possibility of, integrating the masses in the social fabric, also by universally extending the benefits of modern medicine. In fact, there was the need to have millions of soldiers in good health and well-looked after when injured, while the industry benefited from millions of workers in good physical conditions and able to work in factories for many consecutive hours. These were the years when mass hygiene facilities and vaccination campaigns were introduced, and several epidemics were eradicated (cf. Pinker, 2018).

New Potential Inequalities

The economic and military dynamics of the twenty-first century might be very different from the past. In the era of drones and remote or self-driving military vehicles, mass armies are no longer needed: what is needed are only a few selected super-experts in war technology (Scharre, 2018). The advent of robotics and the use of big data combined with evolving algorithms also make a large part of human work obsolete, so that production tasks can be performed by machines, leaving human beings in charge of more complex activities such as design and supervision (Ford, 2015).

These trends, of which we can already see some indications, could be accentuated and accelerated by the research on cognitive enhancement: the best performing individuals will be the ones to occupy positions of responsibility, as society will want to entrust the most important tasks to those with the best skills (Santoni de Sio et al., 2014). There are also scenarios that seem to come from a dystopian novel and, to the current state of knowledge, are certainly not realistic: such scenarios involve the emergence of superhumans with exceptional physical, emotional and intellectual abilities, which will stand out from the rest of the non-enhanced or less enhanced individuals, because the differences will become not only quantitative but also qualitative, leading to the creation of different groups distinguished by temperament and interests (Bess, 2015).

In fact, quantitative differences concern the increase of cognitive abilities, for example memory. Those who can access these forms of empowerment become high-performing people, who can succeed in the workplace and then improve their condition outperforming those who are not enhanced. Qualitative differences instead are brought on, for example, by genetic modifications thanks to recent techniques such as CRISPR-Cas9 (Lavazza, 2019a). In that case, genetically modified individuals could be different from non-modified individuals in the same way as adults and children or the most educated people and the illiterate ones are different. And social consequences would be predictably very relevant.

The equality project entailed by the material and moral progress of the world so far—which substantially amounts to defeating hunger, diseases and war—aims to guarantee decent living conditions for everyone, so that all people can equally pursue their own life project. Instead, the new goals aiming at overcoming our mortal and uncertain human condition, mainly thanks to technology, can hardly be within everyone’s reach and, on the contrary, will often be linked to a privileged condition reserved for a few.

There has certainly been an increase in do-it-yourself use of simple transcranial direct current stimulation (tDCS) devices (Fitz and Reiner, 2015). However, dealing with the use of other latest generation electroceuticals and future more sophisticated devices we will have to address the challenge outlined above. Should we consider prohibiting the use of certain forms of enhancement or should we pursue egalitarian policies, allowing everyone to access electroceuticals? (Lavazza, 2019b). A possible (but debatable) solution is to try to enhance the moral abilities of individuals, to ensure the prevalence of pro-social motives and a general growth of the well-being of individuals and of whole society (Persson and Savulescu, 2012). If this was not possible, one could explore a use of cognitive enhancement according to Rawls’s influential view that inequalities are acceptable if they benefit the whole society (Lavazza, 2016). In this sense, cognitively enhancing certain professional figures or public decision-makers will give them a benefit that others will not enjoy but will positively reverberate on the general functioning of society.

Mandatory Enhancement?

The second challenge concerning electroceuticals is intertwined with the first, while it has a different scope. The processes of scientific and technological innovation on a global scale, along with the phenomena of social complexification, are undergoing continuous acceleration, which will require a greater availability of cognitive skills to manage this complexity and the associated problems (for example, those related to climate change and to the reduction of natural resources). According to Rindermann (2018), however, cognitive abilities in the Western world could go down due to demographic trends. In many nations, fewer births and a longer life expectancy result in a decline in memory, processing speed, attention, creativity and, therefore, in the capacity for innovation. Furthermore, the most educated and cognitively most capable people normally make fewer children.

It is difficult to quantify the phenomenon, both because it is new and because it is still little studied. However, it is plausible to assume that general aging will cause a decrease in the overall cognitive abilities of society. First, there will be more people over the age of 65, while people under the age of 65 will decrease in number. And it is established that “the normal aging process is associated with declines in certain cognitive abilities, such as processing speed and some aspects of memory, language, visuospatial function, and executive functions” (Harada et al., 2013; cf. also Reichman et al., 2010Salthouse, 2012Fechner et al., 2019). Secondly, with the number of elderly people increasing, even if the incidence rate remains fixed, the overall percentage of people suffering from diseases that affect cognition will increase. In the United States today there are about 6 million people with dementia; according to some estimates (Alzheimer’s Association, 2019) the number will go up to 14 million in 2050, while the overall population will remain stable or grow slightly.

The idea of making enhancement (and cognitive improvement/rehabilitation for aged people) widespread and perhaps even mandatory also comes from arguments that underline how some emergencies cannot be faced with the cognitive and moral endowments that we have today (Lavazza and Reichlin, 2019). Persson and Savulescu (2012), for example, have stated that humans are ethically unfit to face the challenges of the present age. Their argument rests on the fact that today’s humankind is facing two kind of threats “generated by the existence of modern scientific technology: the threats of weapons of mass destruction, especially in the hands of terrorist groups, and of climate change and environmental degradation” (Persson and Savulescu, 2012: 1). According to the authors, humans are not morally equipped to address such global problems within a democratic system, especially when it comes to environmental problems. Consequently, cognitive enhancement, understood as the basis of moral betterment, could become the object of policies that make it strongly recommended, encouraged, or mandatory.

In this framework, the classic suggestion is to increase the educational programs that allow for the enhancement of cognitive abilities, which constitute human capital. Specifically, reference is often made to cognitive training programs such as the reasoning training proposed by Klauer and Phye (2008). But if neurocognitive enhancement proves to be safe and effective, it promises to be quicker and more easily administrable to a greater percentage of the population compared to traditional programs, since it does not require the conscious and prolonged effort of the subject. In the case of a real decline in the cognitive abilities of a society as a whole, neurocognitive intervention via neural electrical modulation would become one of the viable options in order to improve the condition of the elderly and compensate for the loss of their cognitive skills and to partially rehabilitate people with degenerative diseases.

This would bring about some ethical questions, as well as the pressure to promote and spread forms of enhancement, and improvement for aged people (since they can only regain the previous performance). In this case, those who want to occupy relevant roles in society might be asked or even forced to undergo the enhancement to make up for the general decline in cognitive abilities. Ethical reflection will then be called to clarify the obligations to be enhanced and the rights of those who do not want to alter the functioning of their mind / brain.

This situation does not exclude the tendency linked to the first challenge that I have illustrated. On the one hand, medicine is concentrating on enhancing a lucky few, who could take advantage of the current dynamics to reverse the pursuit of equality that our societies have been implementing for some time (apart from temporary fluctuations in the distribution of income and wealth). On the other hand, demographic decline and aging may require that more people resort to cognitive enhancement, improvement and rehabilitation to compensate for the decrease in the overall capabilities available to address the complex problems we are facing today.

Conclusion

These scenarios find their preconditions in trends that are already in place, but which will not be necessarily realized. However, they seem to deserve attention from all those working in the field of electroceuticals and from public decision-makers, that is, all those who can affect future situations. Philosophers and neuroethicists are entrusted with the task of thinking about these scenarios so as not to be unprepared in case they come true.

In the face of these challenges, however, some lines of intervention can already be hypothesized. Faced with the first challenge—that is, the possible shift from a mainly therapeutic use of electroceuticals to a use aimed at enhancement—a stricter regulation of devices must be promoted (Dubljević, 2015Maslen et al., 2015). Secondly, scientists and clinicians could try to establish guidelines for the use of electroceuticals that should consider not only the safety features but also the possible social consequences of a widespread use of these enhancement techniques. Thirdly, research should be directed primarily at clinical applications, before moving toward the enhancement of healthy subjects.

As for the second challenge, the three recommendations set out above apply as well. More specifically, all operators engaged in medical practices involving electroceuticals should refer to the ethical codes of their respective professions and to international conventions (for example the Oviedo Convention) for the protection of human rights and dignity. All these rules already in force prevent the mandatory administration of medical treatments, except in extraordinary cases that are, or should be, well-specified. It would therefore be important to avoid defining electroceuticals as a non-medical treatment in order to use them only within a legal framework.

Faced with political decisions that could go toward the violation of the rules in force, the scientific community would have the responsibility to highlight the potential risks involved and to actively prevent them as well.

References

[…]

 

Continue —>  Frontiers | The Two-Fold Ethical Challenge in the Use of Neural Electrical Modulation | Neuroscience

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[REVIEW] Strategies to implement and monitor in-home transcranial electrical stimulation in neurological and psychiatric patient populations: a systematic review – Full Text

Abstract

Background

Transcranial electrical stimulation is a promising technique to facilitate behavioural improvements in neurological and psychiatric populations. Recently there has been interest in remote delivery of stimulation within a participant’s home.

Objective

The purpose of this review is to identify strategies employed to implement and monitor in-home stimulation and identify whether these approaches are associated with protocol adherence, adverse events and patient perspectives.

Methods

MEDLINE, Embase Classic + Embase, Emcare and PsycINFO databases and clinical trial registries were searched to identify studies which reported primary data for any type of transcranial electrical stimulation applied as a home-based treatment.

Results

Nineteen published studies from unique trials and ten on-going trials were included. For published data, internal validity was assessed with the Cochrane risk of bias assessment tool with most studies exhibiting a high level of bias possibly reflecting the preliminary nature of current work. Several different strategies were employed to prepare the participant, deliver and monitor the in-home transcranial electrical stimulation. The use of real time videoconferencing to monitor in-home transcranial electrical stimulation appeared to be associated with higher levels of compliance with the stimulation protocol and greater participant satisfaction. There were no severe adverse events associated with in-home stimulation.

Conclusions

Delivery of transcranial electrical stimulation within a person’s home offers many potential benefits and appears acceptable and safe provided appropriate preparation and monitoring is provided. Future in-home transcranial electrical stimulation studies should use real-time videoconferencing as one of the approaches to facilitate delivery of this potentially beneficial treatment.

Introduction

Transcranial electrical stimulation (tES) is a technique used to modulate cortical function and human behaviour. It involves weak current passing through the scalp via surface electrodes to stimulate the underlying brain. A common type of tES is transcranial direct current stimulation (tDCS). Several studies have demonstrated tDCS is capable of modulating cortical function, depending on the direction of current flow [123]. When the anode is positioned over a cortical region, the current causes depolarisation of the neuronal cells, increasing spontaneous firing rates [4]. Conversely, positioning the cathode over the target cortical region causes hyperpolarisation and a decrease in spontaneous firing rates [4]. This modulation of cortical activity can be observed beyond the period of stimulation and is thought to be mediated by mechanisms which resemble long term potentiation and depression [5]. Along similar lines, transcranial alternating current stimulation (tACS) and transcranial random noise stimulation (tRNS) are also forms of tES. Both tACS and tRNS are thought to interact with ongoing oscillatory cortical rhythms in a frequency dependent manner to influence human behaviour [678].

The ability of tES to selectively modulate cortical activity offers a promising tool to induce behavioural change. Indeed, several studies have demonstrated that tES may be a favourable approach to reduce impairment following stroke [9], improve symptoms of neglect [10], or reduce symptoms of depression [11]. While these results appear promising, there remains debate around technical aspects of stimulation along with individual participant characteristics that may influence the reliability of a stimulation response [1213141516171819202122]. However, current evidence does suggest that effects of stimulation may be cumulative, with greater behavioural improvements observed following repeated stimulation sessions [20]. Furthermore, tES has shown potential as a tool for maintenance stimulation, with potential relapses of depression managed by stimulation which continued over several months [2324]. Therefore, it may be that repeated stimulation sessions will become a hallmark of future clinical and research trials aiming to improve behavioural outcomes. This would require participants to attend frequent treatment sessions applied over a number of days, months or years. Given that many participants who are likely to benefit from stimulation are those with higher levels of motor or cognitive impairment, the requirement to travel regularly for treatment may present a barrier, limiting potential clinical utility or ability to recruit suitable research participants [25]. In addition, regular daily treatments would also hinder those who travel from remote destinations to receive this potentially beneficial neuromodulation. Therefore, there is a requirement to consider approaches to safely and effectively deliver stimulation away from the traditional locations of research departments or clinical facilities.

One benefit of tES over other forms of non-invasive brain stimulation, such as repetitive transcranial magnetic stimulation, is the ability to easily transport the required equipment. This opportunity may allow for stimulation to be delivered in a participant’s home, which could represent the mode of delivery for future clinical applications. However, it may be unreasonable to expect that a participant would be capable of managing delivery of tES alone and would likely require some form of training and/or monitoring [25]. Although tES is considered relatively safe [26], stimulation should be delivered within established guidelines to avoid adverse events [27]. Inappropriate delivery of stimulation could result in neural damage, detrimental behavioural effects, irritation, burns or lesions of the skin [282930313233]. Therefore, in order to deliver stimulation safely to the appropriate cortical region, it is likely that in-home stimulation may require some form of monitoring [25].

It is currently unclear what the best approach is to implement and monitor in-home tES. An early paper proposed several guidelines to perform in home tES [34]. However, these guidelines were not based on evidence from published clinical trials as there were none available at the time of publication. One recent systematic review sought to discuss current work in this area and highlighted the need for further research to investigate safety, technical monitoring and assessment of efficacy [35]. Given the recent, and growing, interest in home-based brain stimulation, we felt it was now pertinent to conduct a review to specifically identify strategies employed to implement and monitor the use of in-home tES in neurological and psychiatric populations. The secondary questions were to report protocol adherence, adverse events and patient perspectives of in-home tES. Understanding optimal treatment fidelity for in-home brain stimulation will be instrumental to achieving higher levels of tES useability and acceptance within a participant’s home.[…]

 

via Strategies to implement and monitor in-home transcranial electrical stimulation in neurological and psychiatric patient populations: a systematic review | Journal of NeuroEngineering and Rehabilitation | Full Text

Fig. 2 Cochrane risk of bias tool was used to assess quality of included studies

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[WEB PAGE] Transcranial Direct Current Stimulation Promising for Major Depressive Disorder

Transcranial Electrical Stimulation

Transcranial direct current stimulation has produced mixed results in patients with major depressive disorder.

Transcranial direct current stimulation (tDCS) is an investigative modality for major depressive disorder (MDD) that has shown some promising results.1 Though it has a while before it is approved by the US Food and Drug Administration, clinicians and patients have been clamoring for an effective treatment for MDD that is not associated with harmful adverse effects.As 6.7% of the world’s population has MDD, which is resistant to pharmacotherapy in approximately one-third of cases, the push is on to identify treatment with lasting effects to combat this disabling disorder.1

tDCS refers to the use of a noninvasive, weak electrical current (1 to 2 mA) applied to electrodes on the scalp that modify cortical excitability.1,2 tDCS has been tested with favorable outcomes in individuals with stroke, Alzheimer disease, movement disorders, schizophrenia, and addiction.1,2

A Small but Emerging Body of Evidence

tDCS has produced mixed results in patients with MDD.3 Brunoni and colleagues performed a meta-analysis of individual patient data on 289 participants with MDD (mean age, 47.2 years; 62.3% women) in 6 randomized, sham-controlled studies.3 tDCS significantly improved response compared with sham procedures (34% vs 19%, respectively; odds ratio [OR], 2.44; 95% confidence interval [CI], 1.38-4.32; P=.002). Remission rates were also favorable (23.1% vs 12.7%, respectively; OR, 2.38; 95% CI, 1.22-4.64; P=.002). The trials did not uniformly categorize adverse events, but the researchers noted that both the tDCS and sham groups had similar drop-out rates.

“tDCS efficacy is still small, and it should be optimized,” noted lead author André Russowsky Brunoni, MD, PhD, associate professor at the Institute of Psychiatry at the University of São Paulo Medical School in Brazil. “There are some approaches for increasing its efficacy, such as combining with other therapies and/or increasing the dose, although this has not been systematically tested yet.”

Combination tDCS and Antidepressant Therapy

The SELECT-TDCS trial (ClinicalTrials.gov Identifier: NCT01033084) examined the cognitive effects of tDCS on 120 patients with MDD (mean age, 42 years; 68% women) in a 6-week trial of sertraline 50 mg/d vs placebo and tDCS vs sham procedure.4 As assessed by a battery of neuropsychological tests, such as the Mini-Mental Status Exam and the Montreal Cognitive Assessment, patients in the trial neither benefited nor regressed in their cognitive functioning with treatment.

tDCS for Treatment-Resistant MDD

Martin and colleagues sought to determine whether tDCS could be used for patients for whom 2 different pharmacotherapies were ineffective for MDD.5 In the open-label study, 20 patients (mean age, 47.4 years; 50% women) received tDCS during cognitive emotional therapy sessions 3 times a week for 6 weeks. The 17 completers had their mood, cognition, and emotion processing assessed at baseline, 3 weeks, and 6 weeks. At the end of the study, 41% of the participants experienced a ≥50% improvement in their depression score and none reported serious adverse events. During the stimulation, patients reported mild burning, redness, and tingling, which diminished by the end of the study.

“Current evidence suggests that tDCS when given by itself has limited antidepressant efficacy compared to standard medication treatment and that it is also not effective in more treatment-resistant patients,” said lead author Donel Martin, PhD, clinical neuropsychologist from the School of Psychiatry at the University of New South Wales in Sydney, Australia. “What our results suggest is that if patients complete a task during tDCS, which simultaneously activates relevant dysfunctional brain regions instead of doing nothing at all, better antidepressant effects may be achieved.”

Filling the tDCS Research Gaps

Scientists have yet to clearly elucidate the mechanism of action of low-current electrical stimulation with tDCS.2 Still to be discovered: how tDCS modulates neurons, how it affects the neural networks, and how the currents change behavior. When clinicians have a better understanding of the underlying mechanisms, they will be better equipped to select the appropriate patients, administer optimal dosages, pair with synergistic antidepressants, and accurately place the electrodes.

Co-author Opher Donchin, PhD, head of the biomedical engineering department at Ben-Gurion University of the Negev, Be’er Sheva, Israel, acknowledges that researchers and clinicians still need additional information for tDCS to progress. “[Functional magnetic resonance imaging] of the brain region before applying tDCS will assist in delivering tDCS with spatiotemporal accuracy,” he said. “Focal stimulation using small electrodes (with high-definition tDCS) is crucial in intensifying and restricting current flow around the intended region. Also, an individual’s genetic test to assess the sensitivity towards tDCS will determine subject-specific adjustment of stimulation strength.”

In animal studies, tDCS has demonstrated long-term changes in brain plasticity in subjects with depression, but scientists still do not know how this occurs.6 Although many studies extrapolated from depression trials, more needs to be elucidated about depressive phenotypes (eg, anxious, melancholic).

“The goal of the paper was to provide a rigorous framework so that future research may one day impact clinical care,” explained co-author Sarah H. Lisanby, MD, director of the Division of Translational Research and the Noninvasive Neuromodulation Unit at the National Institute of Mental Health in Bethesda, Maryland. “There is a need for better characterization/phenotyping of patients in a heterogeneous disorder, for rigorous trial designs, for optimizing spatial targeting and dosing such that the stimulation delivered to the brain is well characterized, and opportunities for combining tDCS with established efficacious interventions as an augmentation strategy.”

Summary and Clinical Applicability

The application of tDCS may ameliorate depression in patients with MDD. Despite some positive signals, tDCS remains an investigative therapy in the United States. More rigorous studies — including randomized, sham-controlled, and dose-ranging trials — are needed to determine optimal patient selection.

References

  1. Bennabi D, Haffen E. Transcranial direct current stimulation (tDCS): a promising treatment for major depressive disorderBrain Sci.2018;8(5):81.
  2. Das S, Holland P, Frens MA, Donchin O. Impact of transcranial direct current stimulation (tDCS) on neuronal functionsFront Neurosci. 2016;10:550.
  3. Brunoni AR, Moffa AH, Fregni F, et al. Transcranial direct current stimulation for acute major depressive episodes: meta-analysis of individual patient dataBr J Psychiatry. 2016;208(6):522-531.
  4. Brunoni AR, Tortella G, Benseñor IM, Lotufo PA, Carvalho AF, Fregni F. Cognitive effects of transcranial direct current stimulation in depression: results from the SELECT-TDCS trial and insights for further clinical trialsJ Affect Disord. 2016;202:46-52. doi: 10.1016/j.jad.2016.03.066
  5. Martin DM, Teng JZ, Lo TY, et al. Clinical pilot study of transcranial direct current stimulation combined with Cognitive Emotional Training for medication resistant depression. J Affect Disord. 2018;232:89-95.
  6. Bikson M, Brunoni AR, Charvet LE, et al. Rigor and reproducibility in research with transcranial electrical stimulation: an NIMH-sponsored workshopBrain Stimul. 2018;11(3):465-480.

via Transcranial Direct Current Stimulation Promising for Major Depressive Disorder – Psychiatry Advisor

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[WEB SITE] tDCS application for motor rehabilitation

Neuer Inhalt

An increasing number of studies highlight the potential application of transcranial direct current stimulation (tDCS) for motor rehabilitation in neurological diseases as well as in healthy aging. tDCS is a technique where a constant weak electric current is passed through scalp electrodes and has been shown to modulate excitability in both cortical and subcortical brain areas. Although the results of tDCS interventions for motor rehabilitation are still preliminary, they encourage further research to better understand its therapeutic potential and to inform optimal clinical use.

This collection of articles aims to present the most recent advances in tDCS for motor rehabilitation, addressing topics such as theoretical, methodological, and practical approaches to be considered when designing tDCS-based rehabilitation. Submissions of both experimental and review studies is encouraged.

This collection of articles has not been sponsored and articles have undergone the journal’s standard peer-review process overseen by the Editor-in-Chief and Associate Editors. The Editor-in-Chief and Associate Editors declare no competing interests.

  1. Content Type:Review

    Transcranial direct current stimulation for the treatment of motor impairment following traumatic brain injury

    After traumatic brain injury (TBI), motor impairment is less common than neurocognitive or behavioral problems. However, about 30% of TBI survivors have reported motor deficits limiting the activities of daily…

    Authors:Won-Seok Kim, Kiwon Lee, Seonghoon Kim, Sungmin Cho and Nam-Jong Paik

    Citation:Journal of NeuroEngineering and Rehabilitation 2019 16:14

    Published on: 25 January 2019

  2. Content Type:Review

    Transcranial direct current stimulation for promoting motor function in cerebral palsy: a review

    Transcranial direct current stimulation (tDCS) has the potential to improve motor function in a range of neurological conditions, including Cerebral Palsy (CP). Although there have been many studies assessing …

    Authors:Melanie K. Fleming, Tim Theologis, Rachel Buckingham and Heidi Johansen-Berg

    Citation:Journal of NeuroEngineering and Rehabilitation 2018 15:121

    Published on: 20 December 2018

  3. Content Type:Commentary

    Transcranial direct current stimulation (tDCS) for upper limb rehabilitation after stroke: future directions.

    Transcranial Direct Current Stimulation (tDCS) is a potentially useful tool to improve upper limb rehabilitation outcomes after stroke, although its effects in this regard have shown to be limited so far. Addi…

    Authors:Bernhard Elsner, Joachim Kugler and Jan Mehrholz

    Citation:Journal of NeuroEngineering and Rehabilitation 2018 15:106

    Published on: 15 November 2018

  4. Content Type:Research

    Home-based transcranial direct current stimulation plus tracking training therapy in people with stroke: an open-label feasibility study

    Transcranial direct current stimulation (tDCS) is an effective neuromodulation adjunct to repetitive motor training in promoting motor recovery post-stroke. Finger tracking training is motor training whereby p…

    Authors:Ann Van de Winckel, James R. Carey, Teresa A. Bisson, Elsa C. Hauschildt, Christopher D. Streib and William K. Durfee

    Citation:Journal of NeuroEngineering and Rehabilitation 2018 15:83

    Published on: 18 September 2018

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[ARTICLE] Transcranial direct current stimulation for the treatment of motor impairment following traumatic brain injury – Full Text

Abstract

After traumatic brain injury (TBI), motor impairment is less common than neurocognitive or behavioral problems. However, about 30% of TBI survivors have reported motor deficits limiting the activities of daily living or participation. After acute primary and secondary injuries, there are subsequent changes including increased GABA-mediated inhibition during the subacute stage and neuroplastic alterations that are adaptive or maladaptive during the chronic stage. Therefore, timely and appropriate neuromodulation by transcranial direct current stimulation (tDCS) may be beneficial to patients with TBI for neuroprotection or restoration of maladaptive changes.

Technologically, combination of imaging-based modelling or simultaneous brain signal monitoring with tDCS could result in greater individualized optimal targeting allowing a more favorable neuroplasticity after TBI. Moreover, a combination of task-oriented training using virtual reality with tDCS can be considered as a potent tele-rehabilitation tool in the home setting, increasing the dose of rehabilitation and neuromodulation, resulting in better motor recovery.

This review summarizes the pathophysiology and possible neuroplastic changes in TBI, as well as provides the general concepts and current evidence with respect to the applicability of tDCS in motor recovery. Through its endeavors, it aims to provide insights on further successful development and clinical application of tDCS in motor rehabilitation after TBI.

Background

Traumatic brain injury (TBI) is defined as “an alteration in brain function (loss of consciousness, post-traumatic amnesia, and neurologic deficits) or other evidence of brain pathology (visual, neuroradiologic, or laboratory confirmation of damage to the brain) caused by external force” [1]. The incidence and prevalence of TBI are substantial and increasing in both developing and developed countries. TBI in older age groups due to falling has been on the rise in recent years, becoming the prevalent condition in all age groups [23]. TBI causes broad spectrum of impairments, including cognitive, psychological, sensory or motor impairments [45], which may increase the socioeconomic burdens and reduce the quality of life [67]. Although motor impairment, such as limb weakness, gait disturbance, balance problem, dystonia or spasticity, is less common than neurocognitive or behavioral problems after TBI, about 30% of TBI survivors have reported motor deficits that severely limited activities of daily living or participation [8].

Motor impairment after TBI is caused by both focal and diffuse damages, making it difficult to determine the precise anatomo-clinical correlations [910]. According to previous clinical studies, recovery after TBI also seems worse than that after stroke, although the neuroplasticity after TBI may also play an important role for recovery [11]. Therefore, a single unimodal approach for motor recovery, including conventional rehabilitation, may be limiting, and hence, requiring a novel therapeutic modality to improve the outcome after TBI.

Transcranial direct current stimulation (tDCS) – one of the noninvasive brain stimulation (NIBS) methods – can increase or decrease the cortical excitability according to polarity (anodal vs. cathodal) and be used to modulate the synaptic plasticity to promote long-term functional recovery via long-term depression or potentiation [1213]. Recent clinical trials evaluating patients with stroke have reported the potential benefits of tDCS for motor recovery [14]. Neuroplastic changes after TBI and results from animal studies also suggest that tDCS could improve the motor deficit in TBI, although clinical trials using tDCS for motor recovery in TBI are currently lacking [14].

In this review, we will cover (1) the pathophysiology and possible neuroplastic changes in TBI; (2) physiology of tDCS; (3) current clinical evidence of tDCS in TBI for motor recovery; (4) general current concept of tDCS application for motor recovery; and (5) the future developments and perspectives of tDCS for motor recovery after TBI. Although the scope of motor recovery is wide, this review will focus primarily on the recovery of limb function, especially that of the upper limb. We expect that this review can provide insights on further successful development and clinical application of tDCS in motor rehabilitation after TBI.[…]

 

Continue —> Transcranial direct current stimulation for the treatment of motor impairment following traumatic brain injury | Journal of NeuroEngineering and Rehabilitation | Full Text

Fig. 3Schematic classification of personalized tDCS for motor recovery. Depending on electrode size, shape, and arrangement, tDCS can be broadly classified into a Conventional tDCS, b Customized Electrode tDCS, and c Distributed Array or High-Definition tDCS. Red color represents anodes and blue color represents cathodes

Fig. 5Merged system with tDCS and virtual reality. Patient with TBI can use this system in the hospital setting with the supervision of clinican (a) and can continue to use it at their home with tele-monitored system (b)

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[Abstract] Sham tDCS: A hidden source of variability? Reflections for further blinded, controlled trials

Abstract

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique increasingly used to modulate neural activity in the living brain. In order to establish the neurophysiological, cognitive or clinical effects of tDCS,tDCS most studies compare the effects of active tDCS to those observed with a sham tDCS intervention. In most cases, sham tDCS consists in delivering an active stimulation for a few seconds to mimic the sensations observed with active tDCS and keep participants blind to the intervention. However, to date, sham-controlled tDCS studies yield inconsistent results, which might arise in part from sham inconsistencies. Indeed, a multiplicity of sham stimulation protocols is being used in the tDCS research field and might have different biological effects beyond the intended transient sensations. Here, we seek to enlighten the scientific community to this possible confounding factor in order to increase reproducibility of neurophysiological, cognitive and clinical tDCS studies.

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[ARTICLE] Home-based transcranial direct current stimulation plus tracking training therapy in people with stroke: an open-label feasibility study – Full Text

Abstract

Background

Transcranial direct current stimulation (tDCS) is an effective neuromodulation adjunct to repetitive motor training in promoting motor recovery post-stroke. Finger tracking training is motor training whereby people with stroke use the impaired index finger to trace waveform-shaped lines on a monitor. Our aims were to assess the feasibility and safety of a telerehabilitation program consisting of tDCS and finger tracking training through questionnaires on ease of use, adverse symptoms, and quantitative assessments of motor function and cognition. We believe this telerehabilitation program will be safe and feasible, and may reduce patient and clinic costs.

Methods

Six participants with hemiplegia post-stroke [mean (SD) age was 61 (10) years; 3 women; mean (SD) time post-stroke was 5.5 (6.5) years] received five 20-min tDCS sessions and finger tracking training provided through telecommunication. Safety measurements included the Digit Span Forward Test for memory, a survey of symptoms, and the Box and Block test for motor function. We assessed feasibility by adherence to treatment and by a questionnaire on ease of equipment use. We reported descriptive statistics on all outcome measures.

Results

Participants completed all treatment sessions with no adverse events. Also, 83.33% of participants found the set-up easy, and all were comfortable with the devices. There was 100% adherence to the sessions and all recommended telerehabilitation.

Conclusions

tDCS with finger tracking training delivered through telerehabilitation was safe, feasible, and has the potential to be a cost-effective home-based therapy for post-stroke motor rehabilitation.

Background

Post-stroke motor function deficits stem not only from neurons killed by the stroke, but also from down-regulated excitability in surviving neurons remote from the infarct [1]. This down-regulation results from deafferentation [2], exaggerated interhemispheric inhibition [3], and learned non-use [4]. Current evidence suggests that post-stroke motor rehabilitation therapies should encourage upregulating neurons and should target neuroplasticity through intensive repetitive motor practice [56]. Previously, our group has examined the feasibility and efficacy of a custom finger tracking training program as a way of providing people with stroke with an engaging repetitive motor practice [789]. In this program, the impaired index finger is attached to an electro-goniometer, and participants repeatedly move the finger up and down to follow a target line that is drawn on the display screen. In successive runs, the shape, frequency and amplitude of target line is varied, which forces the participant to focus on the tracking task. In one study, we demonstrated a 23% improvement in hand function (as measured by the Box and Block test; minimal detectable change is 18% [10]) after participants with stroke completed the tracking training program [9]. While our study did not evaluate changes in activity in daily life (ADL) or quality of life (because efficacy of the treatment was not the study objective), the Box and Block test is moderately correlated (r = 0.52) to activities in daily life and quality of life (r = 0.59) [11]. In addition, using fMRI, we showed that training resulted in an activation transition from ipsilateral to contralateral cortical activation in the supplementary motor area, primary motor and sensory areas, and the premotor cortex [9].

Recently, others have shown that anodal transcranial direct current stimulation (tDCS) can boost the beneficial effects of motor rehabilitation, with the boost lasting for at least 3 months post-training [12]. Also, bihemispheric tDCS stimulation (anodal stimulation to excite the ipsilateral side and cathodal stimulation to downregulate the contralateral side) in combination with physical or occupational therapy has been shown to provide a significant improvement in motor function (as measured by Fugl-Meyer and Wolf Motor Function) compared to a sham group [13]. Further, a recent meta-analysis of randomized-controlled trials comparing different forms of tDCS shows that cathodal tDCS is a promising treatment option to improve ADL capacity in people with stroke [14]. Compared to transcutaneous magnetic stimulation (TMS), tDCS devices are inexpensive and easier to operate. Improvement in upper limb motor function can appear after only five tDCS sessions [15], and there are no reports of serious adverse events when tDCS has been used in human trials for periods of less than 40 min at amplitudes of less than 4 mA [16].

Moreover, tDCS stimulation task also seems beneficial for other impairments commonly seen in people post-stroke. Stimulation with tDCS applied for 20 sessions of 30 min over a 4-week period has been shown to decrease depression and improve quality of life in people after a stroke [1718]. Four tDCS sessions for 10 min applied over the primary and sensory cortex in eight patients with sensory impairments more than 10 months post-stroke enhanced tactile discriminative performance [19]. Breathing exercises with tDCS stimulation seems to be more effective than without stimulation in patient with chronic stroke [20], and tDCS has shown promise in treating central post-stroke pain [21]. Finally, preliminary research on the effect of tDCS combined with training on resting-state functional connectivity shows promise to better understand the mechanisms behind inter-subject variability regarding tDCS stimulation [22].

Motor functional outcomes in stroke have declined at discharge from inpatient rehabilitation facilities [2324], likely a result of the pressures to reduce the length of stay at inpatient rehabilitation facilities as part of a changing and increasingly complex health care climate [2526]. Researchers, clinicians, and administrators continue to search for solutions to facilitate and post-stroke rehabilitation after discharge. Specifically, there has been considerable interest in low-cost stroke therapies than can be administered in the home with only a modest level of supervision by clinical professionals.

Home telerehabilitation is a strategy in which rehabilitation in the patient’s home is guided remotely by the therapist using telecommunication technology. If patients can safely apply tDCS to themselves at home, combining telerehabilitation with tDCS would be an easy way to boost therapy without costly therapeutic face-to-face supervision. For people with multiple sclerosis, the study of Charvet et al. (2017) provided tDCS combined with cognitive training, delivered through home telerehabilitation, and demonstrated greater improvement on cognitive measures compared to those who received just the cognitive training [27]. The authors demonstrated the feasibility of remotely supervised, at-home tDCS and established a protocol for safe and reliable delivery of tDCS for clinical studies [28]. Some evidence shows that telerehabilitation approaches are comparable to conventional rehabilitation in improving activities of daily living and motor function for stroke survivors [2930], and that telemedicine for stroke is cost-effective [3132]. A study in 99 people with stroke receiving training using telerehabilitation (either with home exercise program or robot assisted therapy with home program) demonstrated significant improvements in quality of life and depression [33].

A recent search of the literature suggests that to date, no studies combine tDCS with repetitive tracking training in a home telerehabilitation setting to determine whether the combination leads to improved motor rehabilitation in people with stroke. Therefore, the aim of this pilot project was to explore the safety, usability and feasibility of the combined system. For the tDCS treatment, we used a bihemispheric montage with cathodal tDCS stimulation to suppress the unaffected hemisphere in order to promote stroke recovery [34353637]. For the repetitive tracking training therapy, we used a finger tracking task that targets dexterity because 70% of people post-stroke are unable to use their hand with full effectiveness after stroke [38]. Safety was assessed by noting any decline of 2 points or more in the cognitive testing that persists over more than 3 days. We expect day to day variations of 1 digit. Motor decline is defined by a decline of 6 blocks on the Box and Block test due to muscle weakness. This is based on the minimal detectable change (5.5 blocks/min) [10]. The standard error of measurement is at least 2 blocks for the paretic and stronger side. We expect possible variations in muscle tone that could influence the scoring of the test. Usability was assessed through a questionnaire and by observing whether the participant, under remote supervision, could don the apparatus and complete the therapy sessions. Our intent was to set the stage for a future clinical trial to determine the efficacy of this approach.

Methods

Participants

Participants were recruited from a database of people with chronic stroke who had volunteered for previous post-stroke motor therapy research studies at the University of Minnesota. Inclusion criteria were: at least 6 months post-stroke; at least 10 degrees of active flexion and extension motion at the index finger; awareness of tactile sensation on the scalp; and a score of greater than or equal to 24 (normal cognition) on the Mini-Mental State Examination (MMSE) to be cognitively able to understand instructions to don and use the devices [39]. We excluded those who had a seizure within past 2 years, carried implanted medical devices incompatible with tDCS, were pregnant, had non-dental metal in the head or were not able to understand instructions on how to don and use the devices. The study was approved by the University of Minnesota IRB and all enrolled participants consented to be in the study.

Apparatus

tDCS was applied using the StarStim Home Research Kit (NeuroElectrics, Barcelona, Spain). The StarStim system consists of a Neoprene head cap with marked positions for electrode placement, a wireless cap-mounted stimulator and a laptop control computer. Saline-soaked, 5 cm diameter sponge electrodes were used. For electrode placement, we followed a bihemispheric montage [14] involving cathodal stimulation on the unaffected hemisphere with the anode positioned at C3 and the cathode at C4 for participants with left hemisphere stroke, and vice versa for participants with right hemisphere stroke. Stimulation protocols were set by the investigator on a web-based application that communicated with the tDCS control computer. A remote access application (TeamViewer) was also installed on the control computer, as was a video conferencing application (Skype).

The repetitive finger tracking training system was a copy of what we used in our previous stroke studies [789]. The apparatus included an angle sensor mounted to a lightweight brace and aligned with the metacarpophalangeal (MCP) joint of the index finger, a sensor signal conditioning circuit, and a target tracking application loaded on a table computer. Figure 1 shows a participant using the apparatus during a treatment session.

Fig. 1

Fig. 1 Participant with right hemiparesis receiving transcranial direct current magnetic stimulation (tDCS) in their home simultaneous while performing the finger movement tracking task on the tracking computer (left). The tDCS computer (right) shows the supervising investigator, located off-site, who communicated with the participant through the video conferencing application, controlled the tDCS stimulator through web-based software, and controlled the tracking protocols. (Permission was obtained from the participant for the publication of this picture)

[…]

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[WEB SITE] Transcranial Direct Current Stimulation – Video

People have investigated brain stimulation since very early times, in ancient Rome torpedo fish were applied to the heads of some patients to relieve headaches, for instance, by their electrical currents. In 1802, Aldini of Italy applied electrical current to the exposed cortex of the human brain and attempted also to treat melancholia with a voltaic pile.

Human brain connected to cables and computer chips. Image Credit: Mopic / Shutterstock

Human brain connected to cables and computer chips. Image Credit: Mopic / ShutterstockEnter a caption

The voltaic pile led to accelerated interest in electrical brain stimulation to treat various disorders, including mental illness. The results were not always encouraging, of course, and it wasn’t until much later, in the middle of the 20th century, that direct current stimulation was used to alter the excitable patterns of the brain. This led to increased interest in using direct current to treat mania or depression. There was a brief upsurge in the use of electroconvulsive therapy to treat schizophrenia and other mental illnesses, but it came to an end in the last decade of the 20th century. Electrical stimulation of the brain became stigmatized and drug therapy took center stage as far as psychiatric treatment was concerned.

Recently, interest has arisen in electrical stimulation of the brain because of the finding that weak transcranial direct current stimulation (tDCS) of the brain produced changes in polarization and excitable thresholds of the neurons, which lasted long beyond the period of stimulation. This has led many to investigate the nature of the changes and the potential applications of this technique to major depressive disorder, schizophrenia, obsessive-compulsive disorder and other disorders of the mind with a basis in brain functioning.

Transcranial Direct Current Stimulation Method

The technique of tDCS depends upon non-invasive stimulation of the brain through the skull, by a small constant current applied through scalp electrodes to the head. This leads to currents flowing through the superficial cortex. The strength of the current is so low that it does not directly cause an action potential in the brain neurons, and so instead regulates the excitability of the brain by making them more or less refractory to other endogenous stimulation according to the polarity of the electrodes. Anodal current is generally stimulatory by inducing increased excitability, but cathodal current reduces it. The effect of a single stimulus lasts for 30-120 minutes.

The way in which the current acts depends upon the polarity and the orientation of the cells. Anodal tDCS produces an inflow of current directed inwardly, which hyperpolarizes the apical dendrites of neurons in the pyramidal cortex, but depolarizes those of the somatic areas. Cathodal tDCS on the other hand leads to the reverse effect. The third factor determining the effect of the current is its dose. The strength of the electrical stimulation may lie between 0.5 and 2 mA, its duration is between 5-40 minutes, and the electrode size ranges from 3-100 cm. By altering these variables, it is possible to regulate the current density and total charge, but it may still be difficult to exactly quantify the total current delivered to the brain because of other factors outside the experimental field, such as scalp and cranial impedance.

The electrodes are placed in accordance with the international Electroencephalogram

System, so that one is on the scalp (the active electrode) and the other on the scalp (bipolar or bicephalic placement) or another part of the body, most commonly the upper arm or the shoulder (termed unipolar or monocephalic placement). The current traces a path from the anode, scalp, cranium, cortex, subcortical region, and cathode, stimulating not only the cortex but deeper structures, both in the deep brain and in the midbrain and spinal cord if unipolar placement is adopted. Secondly, the area stimulated is not confined to that near the electrodes because the current flows into adjoining regions in between and around the electrodes.

Mechanism of tDCS

Electrical stimulation with tDCS seems to produce a two-way modification of post-synaptic neuronal connections which results in the same effects as long-term potentiation or long-term depression of cortical excitability does. This is mediated through NMDA receptors. Glutamate antagonists prevent these long-term effects, while NMDAR agonists increase theiramplitude. Work is still going on as to whether repetitive tDCS could cause a more prolonged alteration of behavior. The stimulation has been found to change motor and emotional functioning, as well as sensory, attention-related, and cognitive responses. It is therefore likely to be useful in several psychiatric disorders. It has been found that glutamate antagonists abolish tDCS after-effects, while NMDA-agonists enhance them.

The Advantages and Disadvantages of tDCS

The technique of tDCS is easy to use, in fact, capable of application at home. It is noninvasive and inexpensive. No serious adverse effects have been noted so far. On the other hand, this very ease of use lends itself to a high potential for misuse, such as recreational use, unsupervised medical use, and unethical use as, for instance, to improve one’s attention span while studying. Its long-term effects are also not well established. Thus while the potential has long been recognized, the implementation of this technique is still not widespread pending proper regulation of its use worldwide.

Further Reading

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[ARTICLE] Transcranial direct current stimulation (tDCS) for upper limb rehabilitation after stroke: future directions. – Full Text

Abstract

Transcranial Direct Current Stimulation (tDCS) is a potentially useful tool to improve upper limb rehabilitation outcomes after stroke, although its effects in this regard have shown to be limited so far. Additional increases in effectiveness of tDCS in upper limb rehabilitation after stroke may for example be achieved by

(1) applying a more focal stimulation approach like high definition tDCS (HD-tDCS),

(2) involving functional imaging techniques during stimulation to identify target areas more exactly,

(3) applying tDCS during Electroencephalography (EEG) (EEG-tDCS),

(4) focusing on an effective upper limb rehabilitation strategy as an effective base treatment after stroke.

Perhaps going even beyond the application of tDCS and applying alternative stimulation techniques such as transcranial Alternating Current Stimulation (tACS) or transcranial Random Noise Stimulation (tRNS) will further increase effectiveness of upper limb rehabilitation after stroke.

Background

Impaired arm function after stroke is both frequent and a considerable burden for people with stroke and their caregivers. An emerging approach for enhancing neural plasticity after acute and chronic brain damage, thus enhancing rehabilitation outcomes in the upper limb rehabilitation after stroke, is non-invasive brain stimulation (NIBS), for example delivered by transcranial direct current stimulation (tDCS) [1]. tDCS is a potentially useful tool for facilitating neural plasticity, because it is relatively inexpensive, easy to administer and safe.

Many small trials regarding the effects of tDCS on arm motor function poststroke were undertaken in the past with partly promising but not conclusive results [23]. Based on these trials a lot of research interest increased in the last 10 to 15 years which still persists. This considerable research interest is a bit surprising first, given the fact that this type of therapy is not used across the board in clinical routine and second, the largest multicenter randomized clinical trial with appropriate methodology including 96 patients did not find clear results in favor of this type of stimulation [4]. A recent network meta-analysis of randomised controlled trials about the effectiveness of tDCS suggested only limited evidence for effectiveness of tDCS after stroke for arm rehabilitation [3]. The optimal stimulation paradigm regarding polarisation, electrode location, amount of direct current applied and stimulation duration still has to be established in order to maximize clinical effectiveness of tDCS [5]. Additionally, doubts emerged that the underlying rationale, the interhemispheric competition model, may be oversimplified or even incorrect [6]. The interhemispheric competition model postulates that a stroke leads to an inhibition of the ipsilateral and to an (over-) excitation of the contralateral brain hemisphere. Hence its clinical implications are to inhibit the contralateral hemisphere and to excited ipsilateral hemisphere. Moreover, electrode positioning and the resulting direction of electric fields as well as variation in head anatomy also modulate stimulation effects [78]. Hence, further approaches may be warranted beyond the approach of neuronavigation prior to stimulation: Additional increases in effectiveness of tDCS in upper limb rehabilitation after stroke may for example be achieved by (1) applying a more focal stimulation approach like high definition tDCS (HD-tDCS), (2) involving functional imaging techniques during stimulation to identify target areas more exactly, (3) applying tDCS during EEG (EEG-tDCS), (4) focusing on an effective upper limb rehabilitation strategy as an effective base treatment after stroke. Perhaps going even beyond the application of tDCS and applying alternative stimulation techniques such as transcranial Alternating Current Stimulation (tACS) [9] or transcranial Random Noise Stimulation (tRNS) [10] will further increase effectiveness of upper limb rehabilitation after stroke.[…]

 

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