Myoung-Hwan Ko

Repetitive Transcranial Magnetic Stimulation–Induced Corticomotor Excitability and Associated Motor Skill Acquisition in Chronic Stroke

Background and Purpose— Although there is some early evidence showing the value of repetitive transcranial magnetic stimulation (rTMS) in stroke rehabilitation, the therapeutic effect of high-frequency rTMS, along with the physiology of rTMS-induced corticomotor excitability supporting motor learning in stroke, has not been established. This study investigated high-frequency rTMS-induced cortical excitability and the associated motor skill acquisition in chronic stroke patients. Methods— Fifteen patients with chronic hemiparetic stroke (13 men; mean age 53.5 years) practiced a complex, sequential finger motor task using their paretic fingers either after 10 Hz or sham rTMS over the contralateral primary motor cortex (M1). Both the changes in the behavior and corticomotor excitability before and after the intervention were examined by measuring the movement accuracy, the movement time, and the motor-evoked potential (MEP) amplitude. A separate repeated-measures ANOVA and correlation statistics were used to determine the main and interaction effects as well as relationship between the changes in the behavioral and corticomotor excitability. Results— High-frequency rTMS resulted in a significantly larger increase in the MEP amplitude than the sham rTMS (P<0.01), and the plastic change was positively associated with an enhanced motor performance accuracy (P<0.05). Conclusions— High-frequency rTMS of the affected motor cortex can facilitate practice-dependent plasticity and improve the motor learning performance in chronic stroke victims.

Time-dependent effect of transcranial direct current stimulation on the enhancement of working memory.

The time-dependent effect of transcranial direct current stimulation (tDCS) on working memory was investigated by applying anodal stimulation over the left prefrontal cortex. This single-blind, sham-controlled crossover study recruited 15 healthy participants. A three-back verbal working-memory task was performed before, during, and 30 min after 1 mA anodal or sham tDCS. Anodal tDCS, compared with sham stimulation, significantly improved working-memory performance. Accuracy of response was significantly increased after 20 min of tDCS application, and was further enhanced after 30 min of stimulation. This effect was maintained for 30 min after the completion of stimulation. These results suggest that tDCS at 1 mA enhances working memory in a time-dependent manner for at least 30 min in healthy participants.

Enhancing the Working Memory of Stroke Patients Using tdcs

Jo JM, Kim Y-H, Ko M-H, Ohn SH, Joen B, Lee KH: Enhancing the working memory of stroke patients using tDCS. Am J Phys Med Rehabil 2009;88:404–409. Objectives:We investigated whether anodal transcranial direct current stimulation over the left dorsolateral prefrontal cortex affected the working memory performance of patients after a stroke. Design:Ten patients (mean age 47.7 yrs) with cognitive deficits after a first-ever stroke participated in this single-blind, crossover, and sham-controlled experiment. Each patient was randomly assigned to undergo two transcranial direct current stimulation sessions: anodal dorsolateral prefrontal cortex and sham stimulation within 48 hrs of a washout period. All participants performed a two-back working memory task before and after the administration of the transcranial direct current stimulation. Accuracy (correction rate), recognition accuracy (correction rate-commission error rate), and response time were measured during each experiment. Results:Repeated-measures analysis of variance indicated a significant interaction effect of transcranial direct current stimulation type and time on the recognition accuracy. Post hoc analyses revealed a significant difference between prestimulation and poststimulation in the anodal stimulation group but not in the sham stimulation group. Regarding the accuracy, the paired t test indicated significant improvement only after anodal transcranial direct current stimulation without a significant interaction effect between the two transcranial direct current stimulation types. The response time was not significantly different in the anodal and sham stimulation groups. Conclusion:Our results demonstrated that anodal transcranial direct current stimulation over the left dorsolateral prefrontal cortex was associated with enhanced working memory performance as indexed by the recognition accuracy in patients after a stroke.

Primary motor cortex activation by transcranial direct current stimulation in the human brain.

Transcranial direct current stimulation (tDCS) can modulate motor cortex excitability in the human brain. We attempted to demonstrate the cortical stimulation effect of tDCS on the primary motor cortex (M1) using functional MRI (fMRI). An fMRI study was performed for 11 right-handed healthy subjects at 1.5 T. Anodal tDCS was applied to the scalp over the central knob of the M1 in the left hemisphere. A constant current with an intensity of 1.0 mA was applied. The total fMRI paradigm consisted of three sessions with a 5-min resting period between each session. Each session consisted of five successive phases (resting-tDCS-tDCS-tDCS-tDCS), and each of the phases was performed for 21s. Our findings revealed that no cortical activation was detected in any of the stimulation phases except the fourth tDCS phase. In the result of group analysis for the fourth tDCS phase, the average map indicated that the central knob of the left primary motor cortex was activated. In addition, there were activations on the left supplementary motor cortex and the right posterior parietal cortex. We demonstrated that tDCS has a direct stimulation effect on the underlying cortex. It seems that tDCS is a useful modality for stimulating a target cortical region.

Facilitative effect of high frequency subthreshold repetitive transcranial magnetic stimulation on complex sequential motor learning in humans

We investigated the effect of repetitive transcranial magnetic stimulation (rTMS) applied to the motor cortex, on the motor learning of sequential finger movements. Fifteen healthy subjects were trained to perform seven sequential finger movements of the left hand. Ten Hertz or sham rTMS with a resting motor threshold of 80% was applied to each subject during the task period. Stimulation with 10Hz rTMS produced a better learning performance in terms of target score and execution time than sham stimulation. We conclude that high-frequency rTMS may modulate the excitability of the motor cortex and facilitate the sequential motor learning process in normal subjects. These findings may provide a basis for the development of therapeutic applications of rTMS in patients with impaired motor skill.

Plasticity of the Attentional Network After Brain Injury and Cognitive Rehabilitation

Background. This study aimed to delineate the cerebral attentional network in patients with traumatic brain injury (TBI) and assess for adaptations in this network in response to a rehabilitation intervention. Methods. Seventeen patients with TBI and 15 healthy subjects underwent functional magnetic resonance imaging (fMRI) using a visuospatial attention task. Ten TBI patients who successfully completed attentional training had a follow-up fMRI. Results. In the TBI patients, fMRI analysis showed more activation in the frontal and temporoparietal lobes, as well as less activation in the anterior cingulated gyrus, SMA, and temporooccipital regions compared to the healthy subjects. Following cognitive training, the TBI patients improved performance of attention tasks accompanied by changes in attentional network activation; the activity of the frontal lobe decreased, whereas activation of the anterior cingulate cortices and precuneus increased. Conclusions. These findings demonstrate the plasticity and training induced redistribution of the visuospatial attentional network in TBI patients.

Improvement of visual scanning after DC brain polarization of parietal cortex in stroke patients with spatial neglect.

Previous studies have demonstrated that transcranial direct current (DC) brain polarization can modulate cortical excitability in the human brain. We investigated the effect of anodal DC brain polarization of right parietal cortex on visuospatial scanning in subacute stroke patients with spatial neglect. The patients underwent two neglect tests - figure cancellation and line bisection - before and immediately after anodal DC or sham in a double-blind protocol. Anodal DC was applied to the scalp over the right posterior parietal cortex (PPC) with an intensity of 2.0 mA for 20 min. Anodal DC brain polarization, but not sham, led to significant improvement in the both neglect tests. These results document a beneficial effect of DC brain polarization on neglect.

Effects of single-dose methylphenidate on cognitive performance in patients with traumatic brain injury: a double-blind placebo-controlled study

Objectives: To determine the effect of a single dose of methylphenidate on the cognitive performance of patients with traumatic brain injury (TBI), and particularly on working memory and visuospatial attention. Design: A double-blind placebo-controlled study. The subjects were randomly divided into an experimental group taking methylphenidate and a control group taking a placebo. Setting: The Department of Rehabilitation Medicine of a university hospital. Subjects: Eighteen subjects with TBI (16 male and two female) were enrolled. Interventions: The patients were given 20 mg methylphenidate or a placebo. Cognitive assessments were performed at three times: before the medication as a baseline, 2 h after medication and at follow-up (48 h later). Main measures: Cognitive assessments consisted of working memory tasks and endogenous visuospatial attention tasks designed using SuperLabPro 2.0 software. Response accuracy and reaction time were measured. Results: There were significant improvements in response accuracy in the methylphenidate group compared with the placebo group for both the working memory and visuospatial attention tasks. A significant decrease in the reaction time was also observed in the methylphenidate group only for the working memory task. Conclusions: The administration of single-dose methylphenidate has an effect in improving cognitive functioning following a TBI. The effects were most prominent regarding the reaction time of the working memory.

Long-term effects of transcranial direct current stimulation combined with computer-assisted cognitive training in healthy older adults.

The aim of the present study was to analyze the long-term effects of transcranial direct current stimulation (tDCS) of the bilateral prefrontal cortex combined with computer-assisted cognitive training on working memory and cognitive function in healthy older adults aged at least 65 years. Forty healthy older adults were enrolled and randomly assigned to two groups: anodal and sham tDCS. All participants completed 10 sessions of computer-assisted cognitive training, combined with tDCS of the bilateral prefrontal cortex. The accuracy of the verbal working memory task and performance of the digit span forward test were significantly improved after computer-assisted cognitive training combined with bifrontal anodal tDCS as compared with that after computer-assisted cognitive training combined with sham tDCS. Moreover, the effect lasts for 4 weeks in the verbal working memory task. We suggest that the tDCS-induced changes in the bilateral prefrontal excitability during computer-assisted cognitive training may have beneficial effects on age-related cognitive decrement in healthy older adults.

Suppression of Seizure by Cathodal Transcranial Direct Current Stimulation in an Epileptic Patient - A Case Report -

Epilepsy is an intractable disease, though many treatment modalities have been developed. Recently, noninvasive transcranial direct current stimulation (tDCS), which can change brain excitability, was introduced and has been applied for therapeutic purposes regarding epilepsy. A suppression of seizures was experienced by cathodal tDCS in a medication refractory pediatric epileptic patient. The patient was an 11-year-old female who had focal cortical dysplasia of the cerebral hemisphere. The patient was treated with antiepileptic drugs but the mean seizure frequency was still eight episodes per month. The tDCS cathode was placed at the midpoint of P4 and T4 in the 10-20 EEG system where the abnormal wave was observed on a sleep EEG. Two mA of tDCS was applied 20 minutes a day, five days a week for two weeks. During a two-month period after treatment termination, only six seizure attacks occurred, and the duration of each seizure episode also decreased. tDCS was applied under the same conditions for another two weeks. For two months after the second treatment session, only one seizure attack occurred, and it showed great improvement compared to the eight seizure attacks per month before the tDCS treatment. The medications were not changed, and there were no notable side effects that were caused by tDCS.