Kunitsugu Kondo

Changes in reciprocal Ia inhibition during voluntary contraction in man

SummaryReciprocal Ia inhibition from ankle flexors to extensors was studied during voluntary tonic isometric dorsiflexion and plantar flexion in five normal subjects. The Ia inhibition was examined as the short-latency suppression of the soleus H-reflexes by stimulation of the low-threshold afferents in the common peroneal nerve (Mizuno et al. 1971). At rest, weak Ia inhibition was demonstrated in four subjects out of five, the maximal amount being 14.1 ± 5.0% suppression of the control H-reflex. The absolute amount of inhibition, which was calculated by subtracting the mean size of the conditioned H-reflex from that of the control H-reflex and expressed as a percentage of the maximal M-response, increased during ankle dorsiflexion, and decreased or disappeared during plantar flexion in parallel with the amount of contraction. The neural mechanisms for facilitation of the Ia inhibitory pathway during dorsiflexion were considered to support the hypothesis of “α-γ-linkage in reciprocal inhibition”, i.e. combined facilitatory effects on the Ia inhibitory interneurone from the supraspinal centers directly and indirectly via the γ motoneurone — Ia afferent route. The mechanism for inhibition of the pathway during plantar flexion was considered to be inhibition of the Ia interneurone of the flexor side by Ia interneurone of antagonist extensors. A quantitative aspect of activity in the reciprocal Ia inhibitory pathway on the performance of voluntary movement is revealed in this study.

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.

A new method of estimating the distribution of muscle fiber conduction velocities

A computer-assisted method of estimating the distribution of muscle fiber conduction velocities is described. An electrode array composed of 2 stimulating and 4 recording electrodes is used to record surface muscle action potentials (MAPs) in response to direct muscle stimulation. The velocity distribution and the single muscle fiber action potential (SFAP) are calculated from the recorded MAPs by an iterative method of estimation. The estimation is based on the assumption that the spatial orientation of each muscle fiber viewed from the recording electrodes is the same along the muscle fibers and a MAP is recorded as a linear summation of all SFAPs. The accuracy of this estimation is demonstrated using simulated MAPs. The method is also tested on MAPs containing simulated amplifier noise, stimulus artifact, and errors in distance between electrodes. Finally we applied this method to MAP recordings of the biceps brachii in 23 healthy subjects. The velocity distribution was successfully estimated in 20 cases. The average of the estimated distributions was smaller than that described by previous workers. The reasons for the difference are discussed.

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.

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.

A comparison of the movement characteristics between the kneeling gait and the normal gait in healthy adults.

BACKGROUND Trainings of the kneeling position, such as standing exercise on the knees and kneeling gait, have been anecdotally used in physical therapy to improve postural control of patients with various pathological conditions. However, clinical evidence is lacking and the movement characteristics of these kneeling trainings have not been well explored. The purpose of this study is to clarify the movement characteristics of the kneeling gait compared with the normal gait. METHODS Twenty healthy volunteers (10 men and 10 women) aged 22-34 years were recruited. Participants were required to perform the kneeling gait and the normal gait at a self-selected comfortable speed on the treadmill. Surface electromyograms (EMG) and center of mass (COM) displacements were measured during each task. RESULTS The EMGs of the gait-related proximal muscles during the kneeling gait were greater than during the normal gait, even at a comfortable speed. The COM displacement to the lateral direction was longer during the kneeling gait than it was during the normal gait. Furthermore, mechanical energy efficiency during the kneeling gait was less than that during the normal gait. CONCLUSION The results suggest that the kneeling gait is an effective exercise to strengthen the gait-related proximal muscles. The increased muscle activities during the kneeling gait were probably due to the compensatory movements of the trunk and the pelvis.

Transcranial Direct Current Stimulation Does Not Affect Lower Extremity Muscle Strength Training in Healthy Individuals: A Triple-Blind, Sham-Controlled Study

The present study investigated the effects of anodal transcranial direct current stimulation (tDCS) on lower extremity muscle strength training in 24 healthy participants. In this triple-blind, sham-controlled study, participants were randomly allocated to the anodal tDCS plus muscle strength training (anodal tDCS) group or sham tDCS plus muscle strength training (sham tDCS) group. Anodal tDCS (2 mA) was applied to the primary motor cortex of the lower extremity during muscle strength training of the knee extensors and flexors. Training was conducted once every 3 days for 3 weeks (7 sessions). Knee extensor and flexor peak torques were evaluated before and after the 3 weeks of training. After the 3-week intervention, peak torques of knee extension and flexion changed from 155.9 to 191.1 Nm and from 81.5 to 93.1 Nm in the anodal tDCS group. Peak torques changed from 164.1 to 194.8 Nm on extension and from 78.0 to 85.6 Nm on flexion in the sham tDCS group. In both groups, peak torques of knee extension and flexion significantly increased after the intervention, with no significant difference between the anodal tDCS and sham tDCS groups. In conclusion, although the administration of eccentric training increased knee extensor and flexor peak torques, anodal tDCS did not enhance the effects of lower extremity muscle strength training in healthy individuals. The present null results have crucial implications for selecting optimal stimulation parameters for clinical trials.

Age, Body Mass Index, and White Blood Cell Count Predict the Resumption of Oral Intake in Subacute Stroke Patients

OBJECTIVE To identify the predictors for the resumption of oral feeding at discharge among tube feeding-dependent stroke patients admitted to rehabilitation wards. MATERIALS AND METHODS This study was a retrospective analysis of 107 stroke patients (mean age, 72.1 years) dependent on tube feeds at admission to a rehabilitation ward. Data analyzed included demographic information, severity of impairments, functional independence, body mass index, nutritional and inflammatory laboratory markers at admission, and videofluoroscopic examination findings, if conducted. The variables were compared between the groups with and without resumption of oral intake. The predictive factors for resumption of oral intake were analyzed by using a stepwise multiple logistic regression model. RESULTS At discharge, 69.2% (74 of 107) of the patients resumed oral intake. There were significant differences in age, the Functional Independence Measure, body mass index, serum albumin, C-reactive protein, white blood cell count, and duration of stroke onset at admission between the 2 groups. Multiple logistic regression analysis identified age (odds ratio [OR] .55; 95% confidence interval [CI] .31-.95), body mass index (OR 1.34; 95% CI 1.12-1.60), and white blood cell count (OR .76; 95% CI .60-.97) as significant predictors for the resumption of oral intake in these patients. CONCLUSION Older age, lower body mass index, and higher white blood cell count were significant independent negative predictors for the resumption of oral feeding among stroke patients dependent on tube feeding at admission to rehabilitation wards.