Tomofumi Yamaguchi

Dual-hemisphere transcranial direct current stimulation improves performance in a tactile spatial discrimination task

OBJECTIVE The aim of this study was to test the hypothesis that dual-hemisphere transcranial direct current stimulation (tDCS) over the primary somatosensory cortex (S1) could improve performance in a tactile spatial discriminative task, compared with uni-hemisphere or sham tDCS. METHODS Nine healthy adults participated in this double-blind, sham-controlled, and cross-over design study. The performance in a grating orientation task (GOT) in the right index finger was evaluated before, during, immediately after and 30min after the dual-hemisphere, uni-hemisphere (1mA, 20min), or sham tDCS (1mA, 30s) over S1. In the dual-hemisphere and sham conditions, anodal tDCS was applied over the left S1, and cathodal tDCS was applied over the right S1. In the uni-hemisphere condition, anodal tDCS was applied over the left S1, and cathodal tDCS was applied over the contralateral supraorbital front. RESULTS The percentage of correct responses on the GOT during dual-hemisphere tDCS was significantly higher than that in the uni-hemisphere or sham tDCS conditions when the grating width was set to 0.75mm (all p<0.05). CONCLUSIONS Dual-hemisphere tDCS over S1 improved performance in a tactile spatial discrimination task in healthy volunteers. SIGNIFICANCE Dual-hemisphere tDCS may be a useful strategy to improve sensory function in patients with sensory dysfunctions.

The effect of active pedaling combined with electrical stimulation on spinal reciprocal inhibition

OBJECTIVE Pedaling is widely used for rehabilitation of locomotion because it induces muscle activity very similar to locomotion. Afferent stimulation is important for the modulation of spinal reflexes. Furthermore, supraspinal modulation plays an important role in spinal plasticity induced by electrical stimulation. We, therefore, expected that active pedaling combined with electrical stimulation could induce strong after-effects on spinal reflexes. DESIGN Twelve healthy adults participated in this study. They were instructed to perform 7 min of pedaling. We applied electrical stimulation to the common peroneal nerve during the extension phase of the pedaling cycle. We assessed reciprocal inhibition using a soleus H-reflex conditioning-test paradigm. The magnitude of reciprocal inhibition was measured before, immediately after, 15 and 30 min after active pedaling alone, electrical stimulation alone and active pedaling combined with electrical stimulation (pedaling + ES). RESULTS The amount of reciprocal inhibition was significantly increased after pedaling + ES. The after-effect of pedaling + ES on reciprocal inhibition was more prominent and longer lasting compared with pedaling or electrical stimulation alone. CONCLUSIONS Pedaling + ES could induce stronger after-effects on spinal reciprocal inhibitory neurons compared with either intervention alone. Pedaling + ES might be used as a tool to improve locomotion and functional abnormalities in the patient with central nervous lesion.

Combined effect of motor imagery and peripheral nerve electrical stimulation on the motor cortex

Although motor imagery enhances the excitability of the corticospinal tract, there are no peripheral afferent inputs during motor imagery. In contrast, peripheral nerve electrical stimulation (ES) can induce peripheral afferent inputs; thus, a combination of motor imagery and ES may enhance the excitability of the corticospinal tract compared with motor imagery alone. Moreover, the level of stimulation intensity may also be related to the modulation of the excitability of the corticospinal tract during motor imagery. Here, we evaluated whether a combination of motor imagery and peripheral nerve ES influences the excitability of the corticospinal tract and measured the effect of ES intensity on the excitability induced during motor imagery. The imagined task was a movement that involved touching the thumb to the little finger, whereas ES involved simultaneous stimulation of the ulnar and median nerves at the wrist. Two different ES intensities were used, one above the motor threshold and another above the sensory threshold. Further, we evaluated whether actual movement with afferent input induced by ES modulates the excitability of the corticospinal tract as well as motor imagery. We found that a combination of motor imagery and ES enhanced the excitability of the motor cortex in the thenar muscle compared with the other condition. Furthermore, we established that the modulation of the corticospinal tract was related to ES intensity. However, we found that the excitability of the corticospinal tract induced by actual movement was enhanced by peripheral nerve ES above the sensory threshold.

Transcranial direct current stimulation over the primary and secondary somatosensory cortices transiently improves tactile spatial discrimination in stroke patients

In healthy subjects, dual hemisphere transcranial direct current stimulation (tDCS) over the primary (S1) and secondary somatosensory cortices (S2) has been found to transiently enhance tactile performance. However, the effect of dual hemisphere tDCS on tactile performance in stroke patients with sensory deficits remains unknown. The purpose of this study was to investigate whether dual hemisphere tDCS over S1 and S2 could enhance tactile discrimination in stroke patients. We employed a double-blind, crossover, sham-controlled experimental design. Eight chronic stroke patients with sensory deficits participated in this study. We used a grating orientation task (GOT) to measure the tactile discriminative threshold of the affected and non-affected index fingers before, during, and 10 min after four tDCS conditions. For both the S1 and S2 conditions, we placed an anodal electrode over the lesioned hemisphere and a cathodal electrode over the opposite hemisphere. We applied tDCS at an intensity of 2 mA for 15 min in both S1 and S2 conditions. We included two sham conditions in which the positions of the electrodes and the current intensity were identical to that in the S1 and S2 conditions except that current was delivered for the initial 15 s only. We found that GOT thresholds for the affected index finger during and 10 min after the S1 and S2 conditions were significantly lower compared with each sham condition. GOT thresholds were not significantly different between the S1 and S2 conditions at any time point. We concluded that dual-hemisphere tDCS over S1 and S2 can transiently enhance tactile discriminative task performance in chronic stroke patients with sensory dysfunction.

Anodal Transcranial Direct Current Stimulation over the Lower Limb Motor Cortex Increases the Cortical Excitability with Extracephalic Reference Electrodes

The aim of the present study was to investigate whether anodal transcranial direct-current stimulation (tDCS) of lower-limb primary motor cortex (M1) could increase cortical excitability when reference electrodes were placed at extracephalic positions. Ten healthy volunteers participated in this study. Anodal electrodes were placed over the left lower-limb M1, whereas reference electrodes were placed on the contralateral forehead (cephalic condition) or contralateral upper arm (extracephalic condition). Motor evoked potentials (MEPs) were recorded as a measure of cortical excitability before and after tDCS (2 mA, 10 minutes). Compared with a sham condition, MEPs significantly increased for both cephalic and extracephalic conditions, and this increase was maintained for approximately 60 minutes after stimulation. No side effects were reported. We conclude that tDCS over lower-limb M1 in conjunction with extracephalic reference electrodes can increase cortical excitability without any side effects.

Real-Time Changes in Corticospinal Excitability during Voluntary Contraction with Concurrent Electrical Stimulation

While previous studies have assessed changes in corticospinal excitability following voluntary contraction coupled with electrical stimulation (ES), we sought to examine, for the first time in the field, real-time changes in corticospinal excitability. We monitored motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation and recorded the MEPs using a mechanomyogram, which is less susceptible to electrical artifacts. We assessed the MEPs at each level of muscle contraction of wrist flexion (0%, 5%, or 20% of maximum voluntary contraction) during voluntary wrist flexion (flexor carpi radialis (FCR) voluntary contraction), either with or without simultaneous low-frequency (10 Hz) ES of the median nerve that innervates the FCR. The stimulus intensity corresponded to 1.2× perception threshold. In the FCR, voluntary contraction with median nerve stimulation significantly increased corticospinal excitability compared with FCR voluntary contraction without median nerve stimulation (p<0.01). In addition, corticospinal excitability was significantly modulated by the level of FCR voluntary contraction. In contrast, in the extensor carpi radialis (ECR), FCR voluntary contraction with median nerve stimulation significantly decreased corticospinal excitability compared with FCR voluntary contraction without median nerve stimulation (p<0.05). Thus, median nerve stimulation during FCR voluntary contraction induces reciprocal changes in cortical excitability in agonist and antagonist muscles. Finally we also showed that even mental imagery of FCR voluntary contraction with median nerve stimulation induced the same reciprocal changes in cortical excitability in agonist and antagonist muscles. Our results support the use of voluntary contraction coupled with ES in neurorehabilitation therapy for patients.

Immediate effects of electrical stimulation combined with passive locomotion-like movement on gait velocity and spasticity in persons with hemiparetic stroke: a randomized controlled study

Objective: Research to examine the immediate effects of electrical stimulation combined with passive locomotion-like movement on gait velocity and spasticity. Design: A single-masked, randomized controlled trial design. Subjects: Twenty-seven stroke inpatients in subacute phase (ischemic n=16, hemorrhagic n=11). Interventions: A novel approach using electrical stimulation combined with passive locomotion-like movement. Main measures: We assessed the maximum gait speed and modified Ashworth scale before and 20 minutes after the interventions. Results: The gait velocity of the electrical stimulation combined with passive locomotion-like movement group showed the increase form 0.68±0.28 (mean±SD, unit: m) to 0.76±0.32 after the intervention. Both the electrical stimulation group and passive locomotion-like movement group also showed increases after the interventions (from 0.76±0.37 to 0.79±0.40, from 0.74±0.35 to 0.77±0.36, respectively). The gait velocity of the electrical stimulation combined with passive locomotion-like movement group differed significantly from those of the other groups (electrical stimulation combined with passive locomotion-like movement versus electrical stimulation: P=0.049, electrical stimulation combined with passive locomotion-like movement versus passive locomotion-like movement: P=0.025). Although there was no statistically significant difference in the modified Ashworth scale among the three groups, six of the nine subjects (66.6%) in the electrical stimulation combined with passive locomotion-like movement group showed improvement in the modified Ashworth scale score, while only three of the nine subjects (33.3%) in the electrical stimulation group and two of the nine subjects (22.2%) improved in the passive locomotion-like movement group. Conclusion: These findings suggest electrical stimulation combined with passive locomotion-like movement could improve gait velocity in stroke patients.

A pilot study of contralateral homonymous muscle activity simulated electrical stimulation in chronic hemiplegia.

Objective: For the recovery of hemiparetic hand function, a therapy was developed called contralateral homonymous muscle activity stimulated electrical stimulation (CHASE), which combines electrical stimulation and bilateral movements, and its feasibility was studued in three chronic stroke patients with severe hand hemiparesis. Methods: Patients with a subcortical lesion were asked to extend their wrist and fingers bilaterally while an electromyogram (EMG) was recorded from the extensor carpi radialis (ECR) muscle in the unaffected hand. Electric stimulation was applied to the homonymous wrist and finger extensors of the affected side. The intensity of the electrical stimulation was computed based on the EMG and scaled so that the movements of the paretic hand looked similar to those of the unaffected side. The patients received 30-minutes of therapy per day for 2 weeks. Results: Improvement in the active range of motion of wrist extension was observed for all patients. There was a decrease in the scores of modified Ashworth scale in the flexors. Fugl-Meyer assessment scores of motor function of the upper extremities improved in two of the patients. Conclusions: The results suggest a positive outcome can be obtained using the CHASE system for upper extremity rehabilitation of patients with severe hemiplegia.

After-effects of pedaling exercise on spinal excitability and spinal reciprocal inhibition in patients with chronic stroke.

Purpose of the study: To evaluate the after-effects of pedaling on spinal excitability and spinal reciprocal inhibition in patients with post-stroke spastic hemiparesis. Materials and methods: Twenty stroke patients with severe hemiparesis participated in this study and were instructed to perform 7 min of active pedaling and 7 min of passive pedaling with a recumbent ergometer at a comfortable speed. H reflexes and M waves of paretic soleus muscles were recorded at rest before, immediately after and 30 min after active and passive pedaling. The Hmax/Mmax ratio and H recruitment curve were measured. Reciprocal inhibition was assessed using the soleus H reflex conditioning test paradigm. Results: The Hmax/Mmax ratio was significantly decreased after active and passive pedaling exercise. The decreased Hmax/Mmax ratio after active pedaling lasted at least for 30 min. The H recruitment curve and reciprocal inhibition did not change significantly after active or passive pedaling exercise. Conclusions: Pedaling exercise decreased spinal excitability in patients with severe hemiparesis. Pedaling may be effective in rehabilitation following stroke.

Time-dependent changes in motor cortical excitability by electrical stimulation combined with voluntary drive.

Prolonged changes in primary motor cortex excitability in response to combined neuromuscular electrical stimulation (NMES) and voluntary contraction with motor evoked potentials (MEPs) were investigated by transcranial magnetic stimulation and recorded by mechanomyography. Participants included 22 healthy individuals. NMES was applied to the extensor carpi radialis (ECR) by voluntary ECR contraction with 20% maximum voluntary contraction (MVC) of wrist extension. MEPs were recorded from the flexor carpi radialis (FCR) and ECR at rest with NMES, at 20% MVC with NMES (combined), and at 20% MVC alone. Significant conditional effects were revealed in ECR and FCR. In the combined condition, MEPs showed gradual enhancement, and those in FCR were more inhibited than those in the control condition. Voluntary contraction with NMES increased primary motor cortex excitability in the agonist muscle, whereas the antagonist muscle might affect reciprocal modulation in the combined condition.