Posts Tagged tES
[ARTICLE] A review of transcranial electrical stimulation methods in stroke rehabilitation – Full Text
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., 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.
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.,
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.,, Recently, tDCS has also been tried on normal individuals and was shown to improve cognition, working memory, and performance.,, 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.
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.[…]
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[Abstract] Basic and functional effects of transcranial Electrical Stimulation (tES)—An introduction
We propose to fuse two currently separate research lines on novel therapies for stroke rehabilitation: brain-computer interface (BCI) training and transcranial electrical stimulation (TES). Speciﬁcally, we show that BCI technology can be used to learn personalized decoding models that relate the global conﬁguration of brain rhythms in individual subjects (as measured by EEG) to their motor performance during 3D reaching movements. We demonstrate that our models capture substantial across-subject heterogeneity, and argue that this heterogeneity is a likely cause of limited effect sizes observed in TES for enhancing motor performance. We conclude by discussing how our personalized models can be used to derive optimal TES parameters, e.g., stimulation site and frequency, for individual patients.
Motor deﬁcits are one of the most common outcomes of stroke. According to the World Health Organization, 15 million people worldwide suffer a stroke each year. Of these, ﬁve million are permanently disabled. For this third, upper limb weakness and loss of hand function are among the most devastating types of disabilities, which affect the quality of their daily life . Despite a wide range of rehabilitation therapies, including medication treatment , conventional physiotherapy , and robot physiotherapy , only approximately 20% of patients achieve some form of functional recovery in the ﬁrst six months , .
Current research on novel therapies includes neurofeedback training based on brain-computer interface (BCI) technology and transcranial electrical stimulation (TES). The former approach attempts to support cortical reorganization by providing haptic feedback with a robotic exoskeleton that is congruent to movement attempts, as decoded in real-time from neuroimaging data , . The latter type of research aims to reorganize cortical networks in a way that supports motor performance, because post-stroke alterations of cortical networks have been found to correlate with the severity of motor deﬁcits , . While initial evidence suggested that both approaches, BCIbased training  and TES , have a positive impact, the signiﬁcance of these results over conventional physiotherapy was not always achieved by different studies , , .
One potential explanation for the difﬁculty to replicate the initially promising ﬁndings is the heterogeneity of stroke patients. Different locations of stroke-induced structural changes
are likely to result in substantial across-patient variance in the functional reorganization of cortical networks. As a result, not all patients may beneﬁt from the same neurofeedback or stimulation protocol. We thus propose to fuse these two research themes and use BCI technology to learn personalized models that relate the conﬁguration of cortical networks to each patient’s motor deﬁcits. These personalized models may then be used to predict which TES parameters, e.g., spatial location and frequency band, optimally support rehabilitation in each individual patient.
In this study, we address the ﬁrst step towards personalized TES for stroke rehabilitation. Using a transfer learning framework developed in our group , we show how to create personalized decoding models that relate the EEG of healthy subjects during a 3D reaching task to their motor performance in individual trials. We further demonstrate that the resulting decoding models capture substantial acrosssubject heterogeneity, thereby providing empirical support for the need to personalize models. We conclude by reviewing our ﬁndings in the light of TES studies to improve motor performance in healthy subjects, and discuss how personalized TES parameters may be derived from our models.[…]
[Abstract] Transcranial Electrical Stimulation in Post-Stroke Cognitive Rehabilitation: European Psychologist: Vol 21, No 1
The current book starts with an overview of the past, by providing a brief history of how transcranial electrical stimulation has been used to enhance cognition and improve health. The rest of the book discusses current knowledge in the field, and provides an excellent overview of different lines of research, such as those in animals, healthy humans, and patients. The aim of this last chapter is to discuss further directions for research in the field of transcranial electrical stimulation (tES).
Over the different chapters it becomes clear that research using tES has demonstrated improvements in different cognitive and non-cognitive functions, ranging from perception and motor movement to attention, working memory, language, and mathematical abilities. These results show that such improvements are not limited to typical populations but can also affect young adults and the elderly, and neurological and psychiatric patients. These results are indeed promising, but suffer from some limitations that have been discussed in various of these chapters, as well as elsewhere (Pascual-Leone, Horvath, & Robertson, 2012; Rothwell, 2012). Some of these limitations include low sample size, artificial tasks with reduced ecological validity, lack of consistency in the montage that led to the enhancement effects, and need for replication. I will not extend the discussion on these points, as they are rather trivial and are not limited to the current field. Instead I will discuss what I perceive as the directions in which the field of tES should, and hopefully will, go. It was difficult deciding which sections to include in this respect, and I have chosen to limit our discussion to 10 sections. I will conclude the chapter with a brief discussion of the challenges that the field is facing.
Low-intensity transcranial electrical stimulation (tES) methods are a group of noninvasive brain stimulation techniques, whereby currents are applied with intensities typically ranging between 1 and 2 mA, through the human scalp. These techniques have been shown to induce changes in cortical excitability and activity during and after the stimulation in a reversible manner. They include transcranial direct current simulation (tDCS), transcranial alternating current simulation (tACS), and transcranial random noise stimulation (tRNS).
Currently, an increasing number of studies have been published regarding the effects of tES on cognitive performance and behavior. Processes of learning and increases in cognitive performance are accompanied by changes in cortical plasticity. tES can impact upon these processes and is able to affect task execution. Many studies have been based on the accepted idea that by increasing cortical excitability (e.g., by applying anodal tDCS) or coherence of oscillatory activity (e.g., by applying tACS) an increase in performance should be detected; however, a number of studies now suggest that the basic knowledge of the mechanisms of action is insufficient to predict the outcome of applied stimulation on the execution of a cognitive or behavioral task, and so far no standard paradigms for increasing cortical plasticity changes during learning or cognitive tasks have been established.
The aim of this review is to summarize recent findings with regard to the effects of tES on behavior concentrating on the motor and visual areas…