Non-invasive brain stimulation in neurorehabilitation: local and distant effects for motor recovery

Non-invasive brain stimulation (NIBS) may enhance motor recovery after neurological injury through the causal induction of plasticity processes. Neurological injury, such as stroke, often results in serious long-term physical disabilities, and despite intensive therapy, a large majority of brain injury survivors fail to regain full motor function. Emerging research suggests that NIBS techniques, such as transcranial magnetic (TMS) and direct current (tDCS) stimulation, in association with customarily used neurorehabilitative treatments, may enhance motor recovery. This paper provides a general review on TMS and tDCS paradigms, the mechanisms by which they operate and the stimulation techniques used in neurorehabilitation, specifically stroke. TMS and tDCS influence regional neural activity underlying the stimulation location and also distant interconnected network activity throughout the brain. We discuss recent studies that document NIBS effects on global brain activity measured with various neuroimaging techniques, which help to characterize better strategies for more accurate NIBS stimulation. These rapidly growing areas of inquiry may hold potential for improving the effectiveness of NIBS-based interventions for clinical rehabilitation.

Crossmodal encoding of motor sequence memories

In this study, we tested the hypothesis that exposure to specific auditory sequences could lead to the crossmodal induction of new motor memories. Twenty young, healthy participants memorized a melody without moving. Each tone in the memorized melody had previously been associated with a particular finger movement. For ten of the participants, the contour of the melody memorized was congruent to a subsequently performed, but never practiced, finger movement sequence (C group, n = 10). For the other ten participants, the melody memorized was incongruent to the subsequent finger movement sequence (InC group, n = 10). Results showed faster performance of the movement sequence in the C group than in the InC group. This difference in motor performance was most pronounced 6 h after melody learning and then dissipated over 30 days. These results provide evidence of a specific, crossmodal encoding of a movement sequence representation through an auditory sequence with the effect on motor performance lasting for several hours. The findings of this study are significant, as the formation of new motor memories through exposure to auditory stimuli may be useful in rehabilitation settings where the initial encoding of motor memories through physical training is disrupted.

Practice and sleep form different aspects of skill

Performance for skills such as a sequence of finger movements improves during sleep. This has widely been interpreted as evidence for a role of sleep in strengthening skill learning. Here we propose a different interpretation. We propose that practice and sleep form different aspects of skill. To show this, we train 80 subjects on a sequence of key-presses and test at different time points to determine the amount of skill stored in transition (that is, pressing '2' after '3' in '4-3-2-1') and ordinal (that is, pressing '2' in the third ordinal position in '4-3-2-1') forms. We find transition representations improve with practice and ordinal representations improve during sleep. Further, whether subjects can verbalize the trained sequence affects the formation of ordinal but not transition representations. Verbal knowledge itself does not increase over sleep. Thus, sleep encodes different representations of memory than practice, and may mediate conversion of memories between declarative and procedural forms.

Translational neurorehabilitation research in the third world: what barriers to trial participation can teach us

BACKGROUND AND PURPOSE

Most stroke rehabilitation studies have been performed in high-income countries. The aim of this study was to identify the main barriers for patient inclusion in a research protocol performed in Brazil.

METHODS

We evaluated reasons for exclusion of patients in a pilot, randomized, double-blinded clinical trial of stroke rehabilitation. Descriptive statistical analysis was performed.

RESULTS

Only 5.6% of 571 screened patients were included. Recurrent stroke was responsible for exclusion of 45.4% of potentially eligible patients.

CONCLUSIONS

Recurrent stroke represented a big barrier to enroll patients in the protocol. External validity of rehabilitation trials will benefit from definition of study criteria according to regional characteristics of patients, including rates of recurrent stroke.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT01333579.

Learned EEG-based brain self-regulation of motor-related oscillations during application of transcranial electric brain stimulation: feasibility and limitations

Objective: Transcranial direct current stimulation (tDCS) improves motor learning and can affect emotional processing and attention. However, it is unclear whether learned electroencephalography (EEG)-based brain-machine interface (BMI) control during tDCS is feasible, how application of transcranial electric currents during BMI control would interfere with feature-extraction of physiological brain signals and how it affects brain control performance. Here we tested this combination and evaluated stimulation-dependent artifacts across different EEG frequencies and stability of motor imagery-based BMI control.

Approach: Ten healthy volunteers were invited to two BMI-sessions, each comprising two 60-trial blocks. During the trials, learned desynchronization of mu-rhythms (8–15 Hz) associated with motor imagery (MI) recorded over C4 was translated into online cursor movements on a computer screen. During block 2, either sham (session A) or anodal tDCS (session B) was applied at 1 mA with the stimulation electrode placed 1 cm anterior of C4.

Main results: tDCS was associated with a significant signal power increase in the lower frequencies most evident in the signal spectrum of the EEG channel closest to the stimulation electrode. Stimulation-dependent signal power increase exhibited a decay of 12 dB per decade, leaving frequencies above 9 Hz unaffected. Analysis of BMI control performance did not indicate a difference between blocks and tDCS conditions.

Conclusion: Application of tDCS during learned EEG-based self-regulation of brain oscillations above 9 Hz is feasible and safe, and might improve applicability of BMI systems.

Enhancing Hebbian Learning to Control Brain Oscillatory Activity

Sensorimotor rhythms (SMR, 8-15 Hz) are brain oscillations associated with successful motor performance, imagery, and imitation. Voluntary modulation of SMR can be used to control brain-machine interfaces (BMI) in the absence of any physical movements. The mechanisms underlying acquisition of such skill are unknown. Here, we provide evidence for a causal link between function of the primary motor cortex (M1), active during motor skill learning and retention, and successful acquisition of abstract skills such as control over SMR. Thirty healthy participants were trained on 5 consecutive days to control SMR oscillations. Each participant was randomly assigned to one of 3 groups that received either 20 min of anodal, cathodal, or sham transcranial direct current stimulation (tDCS) over M1. Learning SMR control across training days was superior in the anodal tDCS group relative to the other 2. Cathodal tDCS blocked the beneficial effects of training, as evidenced with sham tDCS. One month later, the newly acquired skill remained superior in the anodal tDCS group. Thus, application of weak electric currents of opposite polarities over M1 differentially modulates learning SMR control, pointing to this primary cortical region as a common substrate for acquisition of physical motor skills and learning to control brain oscillatory activity.

Interference with existing memories alters offline intrinsic functional brain connectivity

The notion that already existing memories can be modified after their reactivation has received an increasing amount of experimental support, with empirical data accumulating across species and memory paradigms. However, there is no evidence for systems-level task-free intrinsic signatures of memory modification. Here, using a combination of behavioral, brain stimulation, and neuroimaging paradigms, we report that noninvasive transcranial magnetic stimulation interference with a reactivated motor memory altered offline task-free corticostriatal interregional functional connectivity, reducing it compared to stimulation in which the reactivated memory was intact. Furthermore, the modulated functional connectivity predicted offline memory modification. This reduction in functional connectivity recovered after additional execution of the memorized task, and the interference did not affect control cerebellar-cortical functional connectivity. This demonstrates that intrinsic task-free offline brain activity can be modulated by noninvasive interaction with existing memories and strongly correlates with behavioral measurements of changes in memory strength.

Cortical mechanisms of recovery of function after stroke

Patients who have suffered hemiplegia from stroke may have some spontaneous recovery that is likely due to reorganization within the cerebral cortex. Understanding this physiology should be useful in devising ways to help patients have better improvement. Techniques, such as transcranial magnetic stimulation and neuroimaging with positron emission tomography, can be used to demonstrate the organization of the human motor system and do reveal plastic reorganization in a number of situations. In relation to stroke, the best recoveries are seen when there is preservation of the corticospinal tract from the hemisphere contralateral to the weakness, but it may well be that areas nearby to the normal motor output areas can partially substitute. There is some evidence for increased corticospinal tract activity originating ipsilateral to the hemiplegia in patients, but this may actually be associated with worse recovery. Patterns of use can influence cortical organization and should play a valuable role in rehabilitation. Certain drugs may affect this process either positively or negatively.

Stochastic reinforcement benefits skill acquisition

Learning complex skills is driven by reinforcement, which facilitates both online within-session gains and retention of the acquired skills. Yet, in ecologically relevant situations, skills are often acquired when mapping between actions and rewarding outcomes is unknown to the learning agent, resulting in reinforcement schedules of a stochastic nature. Here we trained subjects on a visuomotor learning task, comparing reinforcement schedules with higher, lower, or no stochasticity. Training under higher levels of stochastic reinforcement benefited skill acquisition, enhancing both online gains and long-term retention. These findings indicate that the enhancing effects of reinforcement on skill acquisition depend on reinforcement schedules.

Nonparetic arm force does not overinhibit the paretic arm in chronic poststroke hemiparesis

OBJECTIVE

To determine whether nonparetic arm force overinhibits the paretic arm in patients with chronic unilateral poststroke hemiparesis.

DESIGN

Case-control neurophysiological and behavioral study of patients with chronic stroke.

SETTING

Research institution.

PARTICIPANTS

Eighty-six referred patients were screened to enroll 9 participants (N=9) with a >6 month history of 1 unilateral ischemic infarct that resulted in arm hemiparesis with residual ability to produce 1Nm of wrist flexion torque and without contraindication to transcranial magnetic stimulation. Eight age- and handedness-matched healthy volunteers without neurologic diagnosis were studied for comparison.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE

Change in interhemispheric inhibition targeting the ipsilesional primary motor cortex (M1) during nonparetic arm force. We hypothesized that interhemispheric inhibition would increase more in healthy controls than in patients with hemiparesis.

RESULTS

Healthy age-matched controls had significantly greater increases in inhibition from their active to resting M1 than patients with stroke from their active contralesional to resting ipsilesional M1 in the same scenario (20%±7% vs -1%±4%, F1,12=6.61, P=.025). Patients with greater increases in contralesional to ipsilesional inhibition were better performers on the 9-hole peg test of paretic arm function.

CONCLUSIONS

Our findings reveal that producing force with the nonparetic arm does not necessarily overinhibit the paretic arm. Though our study is limited in generalizability by the small sample size, we found that greater active contralesional to resting ipsilesional M1 inhibition was related with better recovery in this subset of patients with chronic poststroke.

In vivo assessment of human brain oscillations during application of transcranial electric currents

Brain oscillations reflect pattern formation of cell assemblies’ activity, which is often disturbed in neurological and psychiatric diseases like depression, schizophrenia and stroke. In the neurobiological analysis and treatment of these conditions, transcranial electric currents applied to the brain proved beneficial. However, the direct effects of these currents on brain oscillations have remained an enigma because of the inability to record them simultaneously. Here we report a novel strategy that resolves this problem. We describe accurate reconstructed localization of dipolar sources and changes of brain oscillatory activity associated with motor actions in primary cortical brain regions undergoing transcranial electric stimulation. This new method allows for the first time direct measurement of the effects of non-invasive electrical brain stimulation on brain oscillatory activity and behavior.

Handgrip-Related Activation in the Primary Motor Cortex Relates to Underlying Neuronal Metabolism After Stroke

BACKGROUND

Abnormal task-related activation in primary motor cortices (M1) has been consistently found in functional imaging studies of subcortical stroke. Whether the abnormal activations are associated with neuronal alterations in the same or homologous area is not known.

OBJECTIVE

Our goal was to establish the relationships between M1 measures of motor-task-related activation and a neuronal marker, N-acetylaspartate (NAA), in patients with severe to mild hemiparesis.

METHODS

A total of 18 survivors of an ischemic subcortical stroke (confirmed on T2-weighted images) at more than six months post-onset and 16 age- and sex-matched right-handed healthy controls underwent functional MRI during a handgrip task (impaired hand in patients, dominant hand in controls) and proton magnetic resonance spectroscopy ((1)H-MRS) imaging. Spatial extent and magnitude of blood oxygen level-dependent response (or activation) and NAA levels were measured in each M1. Relationships between activation and NAA were determined.

RESULTS

Compared with controls, patients had a greater extent of contralesional (ipsilateral to impaired hand, P < .001) activation and a higher magnitude of activation and lower NAA in both ipsilesional (P = .008 and P < .001, respectively) and contralesional (P < .0001, P < .05) M1. There were significant negative correlations between extent of activation and NAA in each M1 (P = .02) and a trend between contralesional activation and ipsilesional NAA (P = .08) in patients but not in controls.

CONCLUSIONS

Our results suggest that after stroke greater neuronal recruitment could be a compensatory response to lower neuronal metabolism. Thus, dual-modality imaging may be a powerful tool for providing complementary probes of post-stroke brain reorganization.

Causal role of prefrontal cortex in strengthening of episodic memories through reconsolidation

Memory consolidation is a dynamic process. Reactivation of consolidated memories triggers reconsolidation, a time-limited period during which memories can be modified. Episodic memory refers to our ability to recall specific past events about what happened, including where and when. However, it is unknown whether noninvasive stimulation of the neocortex during reconsolidation might strengthen existing episodic memories in humans. To modify these memories, we applied repetitive transcranial magnetic stimulation (rTMS) over right lateral prefrontal cortex (PFC), a region involved in the reactivation of episodic memories. We report that rTMS of PFC after memory reactivation strengthened verbal episodic memories, an effect documented by improved recall 24 hr postreactivation compared to stimulation of PFC without reactivation and vertex (control site) after reactivation. In contrast, there was no effect of stimulation 1 hr postreactivation (control experiment), showing that memory strengthening is time dependent, consistent with the reconsolidation theory. Thus, we demonstrated that right lateral PFC plays a causal role in strengthening of episodic memories through reconsolidation in humans. Reconsolidation may serve as an opportunity to modify existing memories with noninvasive stimulation of a critical brain region, an issue of fundamental importance for memory research and clinical applications.

Time- but not sleep-dependent consolidation of tDCS-enhanced visuomotor skills

Consolidation of motor skills after training can occur in a time- or sleep-dependent fashion. Recent studies revealed time-dependent consolidation as a common feature of visuomotor tasks. We have previously shown that anodal transcranial direct current stimulation (tDCS) in combination with repeated motor training benefits consolidation by the induction of offline skill gains in a complex visuomotor task, preventing the regular occurrence of skill loss between days. Here, we asked 2 questions: What is the time course of consolidation between days for this task and do exogenously induced offline gains develop as a function of time or overnight sleep? We found that both the development of offline skill loss in sham-stimulated subjects and offline skill gains induced by anodal tDCS critically depend on the passage of time after training, but not on overnight sleep. These findings support the view that tDCS interacts directly with the physiological consolidation process. However, in a control experiment, anodal tDCS applied after the training did not induce skill gains, implying that coapplication of tDCS and training is required to induce offline skill gains, pointing to the initiation of consolidation already during training.

Brain-machine interface in chronic stroke rehabilitation: a controlled study

OBJECTIVE

Chronic stroke patients with severe hand weakness respond poorly to rehabilitation efforts. Here, we evaluated efficacy of daily brain-machine interface (BMI) training to increase the hypothesized beneficial effects of physiotherapy alone in patients with severe paresis in a double-blind sham-controlled design proof of concept study.

METHODS

Thirty-two chronic stroke patients with severe hand weakness were randomly assigned to 2 matched groups and participated in 17.8 ± 1.4 days of training rewarding desynchronization of ipsilesional oscillatory sensorimotor rhythms with contingent online movements of hand and arm orthoses (experimental group, n = 16). In the control group (sham group, n = 16), movements of the orthoses occurred randomly. Both groups received identical behavioral physiotherapy immediately following BMI training or the control intervention. Upper limb motor function scores, electromyography from arm and hand muscles, placebo-expectancy effects, and functional magnetic resonance imaging (fMRI) blood oxygenation level-dependent activity were assessed before and after intervention.

RESULTS

A significant group × time interaction in upper limb (combined hand and modified arm) Fugl-Meyer assessment (cFMA) motor scores was found. cFMA scores improved more in the experimental than in the control group, presenting a significant improvement of cFMA scores (3.41 ± 0.563-point difference, p = 0.018) reflecting a clinically meaningful change from no activity to some in paretic muscles. cFMA improvements in the experimental group correlated with changes in fMRI laterality index and with paretic hand electromyography activity. Placebo-expectancy scores were comparable for both groups.

INTERPRETATION

The addition of BMI training to behaviorally oriented physiotherapy can be used to induce functional improvements in motor function in chronic stroke patients without residual finger movements and may open a new door in stroke neurorehabilitation.

Cortico-subcortical neuronal circuitry associated with reconsolidation of human procedural memories

The ability of the mammalian brain to modify existing memories through reconsolidation may be crucial for skill acquisition. The neural mechanisms of memory modification have been commonly studied at the cellular level. Yet surprisingly, the human brain systems-level mechanisms involved in day-to-day modification of existing procedural memories remain largely unknown. Here, we studied differences in functional magnetic resonance imaging (fMRI) regional signal activity and inter-regional functional connectivity in subjects in whom motor memory modification was interfered with by repetitive transcranial magnetic stimulation (rTMS), relative to subjects with intact memory modification. As a consequence, subjects with impaired memory modification had lower activity in the supplementary motor area (SMA) and weaker functional connectivity between M1, SMA, anterior cerebellum consistently engaged in early learning, and sensorimotor striatum active in later learning stages. These findings, identifying a link between engagement of this network and successful memory modification, suggest that memory reconsolidation may represent a transitional bridge between early and late procedural learning, underlying efficient skill acquisition.

Reversed timing-dependent associative plasticity in the human brain through interhemispheric interactions

Spike timing-dependent plasticity (STDP) has been proposed as one of the key mechanisms underlying learning and memory. Repetitive median nerve stimulation, followed by transcranial magnetic stimulation (TMS) of the contralateral primary motor cortex (M1), defined as paired-associative stimulation (PAS), has been used as an in vivo model of STDP in humans. PAS-induced excitability changes in M1 have been repeatedly shown to be time-dependent in a STDP-like fashion, since synchronous arrival of inputs within M1 induces long-term potentiation-like effects, whereas an asynchronous arrival induces long-term depression (LTD)-like effects. Here, we show that interhemispheric inhibition of the sensorimotor network during PAS, with the peripheral stimulation over the hand ipsilateral to the motor cortex receiving TMS, results in a LTD-like effect, as opposed to the standard STDP-like effect seen for contralateral PAS. Furthermore, we could show that this reversed-associative plasticity critically depends on the timing interval between afferent and cortical stimulation. These results indicate that the outcome of associative stimulation in the human brain depends on functional network interactions (inhibition or facilitation) at a systems level and can either follow standard or reversed STDP-like mechanisms.

Neural plasticity and its contribution to functional recovery

In this chapter we address the phenomena of neural plasticity, operationally defined as the ability of the central nervous system to adapt in response to changes in the environment or lesions. At the cellular level, we discuss basic changes in membrane excitability, synaptic plasticity as well as structural changes in dendritic and axonal anatomy that support behavioral expressions of plasticity and functional recovery. We consider the different levels at which these changes can occur and possible links with modification of cognitive strategies, recruitment of new/different neural networks, or changes in strength of such connections or specific brain areas in charge of carrying out a particular task (i.e., movement, language, vision, hearing). The study of neuroplasticity has wide-reaching implications for understanding reorganization of action and cognition in the healthy and lesioned brain.

Neuroenhancement of the aging brain: restoring skill acquisition in old subjects

OBJECTIVE

Decline in cognitive functions, including impaired acquisition of novel skills, is a feature of older age that impacts activities of daily living, independence, and integration in modern societies.

METHODS

We tested whether the acquisition of a complex motor skill can be enhanced in old subjects by the application of transcranial direct current stimulation (tDCS) to the motor cortex.

RESULTS

The main finding was that old participants experienced substantial improvements when training was applied concurrent with tDCS, with effects lasting for at least 24 hours.

INTERPRETATION

These results suggest noninvasive brain stimulation as a promising and safe tool to potentially assist functional independence of aged individuals in daily life.

Common mechanisms of human perceptual and motor learning

The adult mammalian brain has a remarkable capacity to learn in both the perceptual and motor domains through the formation and consolidation of memories. Such practice-enabled procedural learning results in perceptual and motor skill improvements. Here, we examine evidence supporting the notion that perceptual and motor learning in humans exhibit analogous properties, including similarities in temporal dynamics and the interactions between primary cortical and higher-order brain areas. These similarities may point to the existence of a common general mechanism for learning in humans.

GABAB-ergic motor cortex dysfunction in SSADH deficiency

OBJECTIVE

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a rare autosomal recessive disorder of GABA degradation leading to elevations in brain GABA and γ-hydroxybutyric acid (GHB). The effect of chronically elevated GABA and GHB on cortical excitability is unknown. We hypothesized that use-dependent downregulation of GABA receptor expression would promote cortical disinhibition rather than inhibition, predominantly via presynaptic GABAergic mechanisms.

METHODS

We quantified the magnitude of excitation and inhibition in primary motor cortex (M1) in patients with SSADH deficiency, their parents (obligate heterozygotes), age-matched healthy young controls, and healthy adults using single and paired pulse transcranial magnetic stimulation (TMS).

RESULTS

Long interval intracortical inhibition was significantly reduced and the cortical silent period was significantly shortened in patients with SSADH deficiency compared to heterozygous parents and control groups.

CONCLUSIONS

Since long interval intracortical inhibition and cortical silent period are thought to reflect GABA(B) receptor-mediated inhibitory circuits, our results point to a particularly GABA(B)-ergic motor cortex dysfunction in patients with SSADH deficiency. This human phenotype is consistent with the proposed mechanism of use-dependent downregulation of postsynaptic GABA(B) receptors in SSADH deficiency animal models. Additionally, the results suggest autoinhibition of GABAergic neurons. This first demonstration of altered GABA(B)-ergic function in patients with SSADH deficiency may help to explain clinical features of the disease, and suggest pathophysiologic mechanisms in other neurotransmitter-related disorders.

Independent component analysis of resting brain activity reveals transient modulation of local cortical processing by transcranial direct current stimulation

Neuroplasticity induced by transcranial direct current stimulation (tDCS) contributes to motor learning although the underlying mechanisms are incompletely understood. Here, we investigated the effects of tDCS on resting brain dynamics recorded by whole-head magnetoencephalography (MEG) pre- and up to 35 minutes post-tDCS or sham over the left primary motor cortex (M1) in healthy adults. Owing to superior temporal and spatial resolution of MEG, we sought to apply a robust, blind and data-driven analytic approach such as independent component analysis (ICA) and statistical clustering to these data to investigate potential neuroplastic effects of tDCS during resting state conditions. We found decreased alpha and increased gamma band power that outlasted the real tDCS stimulation period in a fronto-parietal motor network relative to sham. However, this method could not find differences between anodal and cathodal polarities of tDCS. These results suggest that tDCS over M1 modulates resting brain dynamics in a fronto-parietal motor network (that includes the stimulated location), indicative of within-network enhanced localized cortical processing.

Modifying somatosensory processing with non-invasive brain stimulation

Purposeful manipulation of cortical plasticity and excitability within somatosensory regions may have therapeutic potential. Non-invasive brain stimulation (NBS) techniques such as transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) have shown promise towards this end with certain NBS protocols augmenting somatosensory processing and others down-regulating it. Here, we review NBS protocols which, when applied to primary somatosensory cortex, facilitate cortical excitability and tactile acuity (i.e., high-frequency repetitive TMS (rTMS), intermittent theta burst stimulation (TBS), paired associative stimulation (PAS) N20-5 to 0, anodal tDCS), and protocols that inhibit the same (i.e., low-frequency rTMS, continuous TBS, PAS N20-20, cathodal tDCS). Other studies have targeted multisensory regions of the brain to modulate somatosensory processing. These studies in full present a wide array of strategies in which NBS can be utilized to influence somatosensory processing in a behaviorally and clinically relevant capacity.

Modulation of training by single-session transcranial direct current stimulation to the intact motor cortex enhances motor skill acquisition of the paretic hand

BACKGROUND AND PURPOSE

Mechanisms of skill learning are paramount components for stroke recovery. Recent noninvasive brain stimulation studies demonstrated that decreasing activity in the contralesional motor cortex might be beneficial, providing transient functional improvements after stroke. The more crucial question, however, is whether this intervention can also enhance the acquisition of complex motor tasks, yielding longer-lasting functional improvements. In the present study, we tested the capacity of cathodal transcranial direct current stimulation (tDCS) applied over the contralesional motor cortex during training to enhance the acquisition and retention of complex sequential finger movements of the paretic hand.

METHOD

Twelve well-recovered chronic patients with subcortical stroke attended 2 training sessions during which either cathodal tDCS or a sham intervention were applied to the contralesional motor cortex in a double-blind, crossover design. Two different motor sequences, matched for their degree of complexity, were tested in a counterbalanced order during as well as 90 minutes and 24 hours after the intervention. Potential underlying mechanisms were evaluated with transcranial magnetic stimulation.

RESULTS

tDCS facilitated the acquisition of a new motor skill compared with sham stimulation (P=0.04) yielding better task retention results. A significant correlation was observed between the tDCS-induced improvement during training and the tDCS-induced changes of intracortical inhibition (R(2)=0.63).

CONCLUSIONS

These results indicate that tDCS is a promising tool to improve not only motor behavior, but also procedural learning. They further underline the potential of noninvasive brain stimulation as an adjuvant treatment for long-term recovery, at least in patients with mild functional impairment after stroke.

A practical guide to diagnostic transcranial magnetic stimulation: report of an IFCN committee

Transcranial magnetic stimulation (TMS) is an established neurophysiological tool to examine the integrity of the fast-conducting corticomotor pathways in a wide range of diseases associated with motor dysfunction. This includes but is not limited to patients with multiple sclerosis, amyotrophic lateral sclerosis, stroke, movement disorders, disorders affecting the spinal cord, facial and other cranial nerves. These guidelines cover practical aspects of TMS in a clinical setting. We first discuss the technical and physiological aspects of TMS that are relevant for the diagnostic use of TMS. We then lay out the general principles that apply to a standardized clinical examination of the fast-conducting corticomotor pathways with single-pulse TMS. This is followed by a detailed description of how to examine corticomotor conduction to the hand, leg, trunk and facial muscles in patients. Additional sections cover safety issues, the triple stimulation technique, and neuropediatric aspects of TMS.