Cerebellar direct current stimulation enhances motor learning in older adults.

Developing novel approaches to combat age related declines in motor function is key to maintaining health and function in older adults, a subgroup of the population that is rapidly growing. Motor adaptation, a form of motor learning, has been shown to be impaired in healthy older subjects compared with their younger counterparts. Here, we tested whether excitatory anodal transcranial direct current stimulation (tDCS) over the cerebellum could enhance adaptation in older subjects. Participants performed a "center-out" reaching task, adapting to the sudden introduction of a visual cursor rotation. Older participants receiving sham tDCS (mean age 56.3 ± 6.8 years) were slower to adapt than younger participants (mean age 20.7 ± 2.1 years). In contrast, older participants who received anodal tDCS (mean age 59.6 ± 8.1 years) adapted faster, with a rate that was similar to younger subjects. We conclude that cerebellar anodal tDCS enhances motor adaptation in older individuals. Our results highlight the efficacy of the novel approach of using cerebellar tDCS to combat age related deficits in motor learning.

Facilitating skilled right hand motor function in older subjects by anodal polarization over the left primary motor cortex.

Healthy ageing is accompanied by limitations in performance of activities of daily living and personal independence. Recent reports demonstrated improvements in motor function induced by noninvasive anodal direct current stimulation (tDCS) of the primary motor cortex (M1) in young healthy adults. Here we tested the hypothesis that a single session of anodal tDCS over left M1 could facilitate performance of right upper extremity tasks required for activities of daily living (Jebsen-Taylor hand function test, JTT) in older subjects relative to Sham in a double-blind cross-over study design. We found (a) significant improvement in JTT function with tDCS relative to Sham that outlasted the stimulation period by at least 30 min, (b) that the older the subjects the more prominent this improvement appeared and (c) that consistent with previous results in younger subjects, these effects were not accompanied by any overt undesired side effect. We conclude that anodal tDCS applied over M1 can facilitate performance of skilled hand functions required for activities of daily living in older subjects.

Effects of combined peripheral nerve stimulation and brain polarization on performance of a motor sequence task after chronic stroke.

BACKGROUND AND PURPOSE: Recent work demonstrated that application of peripheral nerve and cortical stimulation independently can induce modest improvements in motor performance in patients with stroke. The purpose of this study was to test the hypothesis that combining peripheral nerve stimulation (PNS) to the paretic hand with anodal direct current stimulation (tDCS) to the ipsilesional primary motor cortex (M1) would facilitate beneficial effects of motor training more than each intervention alone or sham (tDCS(Sham) and PNS(Sham)). METHODS: Nine chronic stroke patients completed a blinded crossover designed study. In separate sessions, we investigated the effects of single applications of PNS+tDCS, PNS+tDCS(Sham), tDCS+PNS(Sham), and PNS(Sham)+tDCS(Sham) before motor training on the ability to perform finger motor sequences with the paretic hand. RESULTS: PNS+tDCS resulted in a 41.3% improvement in the number of correct key presses relative to PNS(Sham)+tDCS(Sham), 15.4% relative to PNS+tDCS(Sham), and 22.7% relative to tDCS+PNS(Sham). These performance differences were maintained 1 and 6 days after the end of the training. CONCLUSIONS: These results indicate that combining PNS with tDCS can facilitate the beneficial effects of training on motor performance beyond levels reached with each intervention alone, a finding of relevance for the neurorehabilitation of motor impairments after stroke.

Controversy: Noninvasive and invasive cortical stimulation show efficacy in treating stroke patients.

Stroke is the leading cause of disability in the adult population of western industrialized countries. Despite significant improvements of acute stroke care, two thirds of stroke survivors have to cope with persisting neurologic deficits. Adjuvant brain stimulation is a novel approach to improving the treatment of residual deficits after stroke. Transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and epidural electrical stimulation have been used in first trials on small cohorts of stroke patients. Effect sizes in the order of 8% to 30% of functional improvement have been reported, but a publication bias toward presenting "promising" but not negative results is likely. Many questions regarding underlying mechanisms, optimal stimulation parameters, combination with other types of interventions, among others, are open. This review addresses six controversies related to the experimental application of brain stimulation techniques to stroke patients. Cortical stimulation after stroke will need to be individually tailored and a thorough patient stratification according to type and extent of clinical deficit, lesion location, lesion size, comorbidities, time in the recovery process, and perhaps also age and gender will be necessary. There is consensus that cortical stimulation in stroke patients is still experimental and should only be applied in the frame of scientific studies.

Consensus: Can transcranial direct current stimulation and transcranial magnetic stimulation enhance motor learning and memory formation?

Noninvasive brain stimulation has developed as a promising tool for cognitive neuroscientists. Transcranial magnetic (TMS) and direct current (tDCS) stimulation allow researchers to purposefully enhance or decrease excitability in focal areas of the brain. The purpose of this article is to review information on the use of TMS and tDCS as research tools to facilitate motor memory formation, motor performance, and motor learning in healthy volunteers. Studies implemented so far have mostly focused on the ability of TMS and tDCS to elicit relatively short-lasting motor improvements and the mechanisms underlying these changes have been only partially investigated. Despite limitations, including the scarcity of data, work that has been already accomplished raises the exciting hypothesis that currently available noninvasive transcranial stimulation techniques could modulate motor learning and memory formation in healthy humans and potentially in patients with neurologic and psychiatric disorders.

Somatosensory stimulation enhances the effects of training functional hand tasks in patients with chronic stroke.

OBJECTIVE: To test the hypothesis that somatosensory stimulation would enhance the effects of training functional hand tasks immediately after practice and 1 day later in chronic subcortical stroke patients. DESIGN: Single-blinded and randomized, crossover study. SETTING: Human research laboratory. PARTICIPANTS: Nine chronic subcortical stroke patients. INTERVENTIONS: Three separate sessions of motor training preceded by (1) synchronous peripheral nerve stimulation (PNS), (2) no stimulation, or (3) asynchronous PNS. MAIN OUTCOME MEASURES: Time to complete the Jebsen-Taylor Hand Function Test (JTHFT time) and corticomotor excitability tested with transcranial magnetic stimulation. RESULTS: After familiarization practice, during which all patients reached a performance plateau, training under the effects of PNS reduced JTHFT time by 10% beyond the post-familiarization plateau. This behavioral gain was accompanied by a specific reduction in GABAergically mediated intracortical inhibition in the motor cortex. These findings were not observed after similar practice under the influence of no stimulation or asynchronous PNS sessions. CONCLUSIONS: Somatosensory stimulation may enhance the training of functional hand tasks in patients with chronic stroke, possibly through modulation of intracortical GABAergic pathways.

Noninvasive brain stimulation in stroke rehabilitation.

Stroke is a common disorder that produces a major burden to society, largely through long-lasting motor disability in survivors. Recent studies have broadened our understanding of the processes underlying recovery of motor function after stroke. Bilateral motor regions of the brain experience substantial reorganization after stroke, including changes in the strength of interhemispheric inhibitory interactions. Our understanding of the extent to which different forms of reorganization contribute to behavioral gains in the rehabilitative process, although still limited, has led to the formulation of novel interventional strategies to regain motor function. Transcranial magnetic (TMS) and DC (tDCS) electrical stimulation are noninvasive brain stimulation techniques that modulate cortical excitability in both healthy individuals and stroke patients. These techniques can enhance the effect of training on performance of various motor tasks, including those that mimic activities of daily living. This review looks at the effects of TMS and tDCS on motor cortical function and motor performance in healthy volunteers and in patients with stroke. Both techniques can either enhance or suppress cortical excitability, and may move to the clinical arena as strategies to enhance the beneficial effects of customarily used neurorehabilitative treatments after stroke.

Effects of non-invasive cortical stimulation on skilled motor function in chronic stroke.

Stroke is a leading cause of adult motor disability. Despite recent progress, recovery of motor function after stroke is usually incomplete. This double blind, Sham-controlled, crossover study was designed to test the hypothesis that non-invasive stimulation of the motor cortex could improve motor function in the paretic hand of patients with chronic stroke. Hand function was measured using the Jebsen-Taylor Hand Function Test (JTT), a widely used, well validated test for functional motor assessment that reflects activities of daily living. JTT measured in the paretic hand improved significantly with non-invasive transcranial direct current stimulation (tDCS), but not with Sham, an effect that outlasted the stimulation period, was present in every single patient tested and that correlated with an increment in motor cortical excitability within the affected hemisphere, expressed as increased recruitment curves (RC) and reduced short-interval intracortical inhibition. These results document a beneficial effect of non-invasive cortical stimulation on a set of hand functions that mimic activities of daily living in the paretic hand of patients with chronic stroke, and suggest that this interventional strategy in combination with customary rehabilitative treatments may play an adjuvant role in neurorehabilitation.