Yutaka Oouchida

Motor Control and Neural Plasticity through Interhemispheric Interactions

The corpus callosum, which is the largest white matter structure in the human brain, connects the 2 cerebral hemispheres. It plays a crucial role in maintaining the independent processing of the hemispheres and in integrating information between both hemispheres. The functional integrity of interhemispheric interactions can be tested electrophysiologically in humans by using transcranial magnetic stimulation, electroencephalography, and functional magnetic resonance imaging. As a brain structural imaging, diffusion tensor imaging has revealed the microstructural connectivity underlying interhemispheric interactions. Sex, age, and motor training in addition to the size of the corpus callosum influence interhemispheric interactions. Several neurological disorders change hemispheric asymmetry directly by impairing the corpus callosum. Moreover, stroke lesions and unilateral peripheral impairments such as amputation alter interhemispheric interactions indirectly. Noninvasive brain stimulation changes the interhemispheric interactions between both motor cortices. Recently, these brain stimulation techniques were applied in the clinical rehabilitation of patients with stroke by ameliorating the deteriorated modulation of interhemispheric interactions. Here, we review the interhemispheric interactions and mechanisms underlying the pathogenesis of these interactions and propose rehabilitative approaches for appropriate cortical reorganization.

Prevalence and Length of Recovery of Pusher Syndrome Based on Cerebral Hemispheric Lesion Side in Patients With Acute Stroke

Background and Purpose— The aim of this study was to determine if side of cerebral hemisphere lesion affects the prevalence and time course of pushing behavior (PB) after stroke. Methods— A total of 1660 patients with acute stroke were investigated. PB was assessed using the standardized Scale for Contraversive Pushing. Risk ratios were used to evaluate the differences in the prevalence of PB between right cerebral hemisphere-damaged (RCD) and left cerebral hemisphere-damaged (LCD) patients. The differences in the time course among 35 (27 RCD and 8 LCD) patients were evaluated by analyzing Scale for Contraversive Pushing scores with the Kaplan–Meier method using a log-rank test. Results— PB was observed in 156 (9.4%) patients. The prevalence of PB was significantly higher in RCD (97 of 556 [17.4%]) than in LCD (57 of 599 [9.5%]) patients; risk ratio was 1.83 (95% CI, 1.35–2.49). The log-rank test indicated that RCD patients exhibited a significantly slower recovery than LCD patients (P=0.027). Conclusions— The number of RCD patients who exhibited PB was higher than that of LCD patients. The duration of recovery from PB was longer in RCD patients than in LCD patients.

Importance of precentral motor regions in human kinesthesia: A single case study

Prompted by our neuroimaging findings in 60 normal people, we examined whether focal damage to the hand section of precentral motor regions impairs hand kinesthesia in a patient, and investigated brain regions related to recovery of kinesthetic function. The damage impaired contralateral kinesthesia. The peri-lesional cerebral motor region, together with the ipsilateral intermediate cerebellum, participated in the recovered kinesthetic processing. The study confirmed the importance of precentral motor regions in human kinesthesia, and indicated a contribution of the peri-lesional cerebral region in recovered kinesthesia after precentral damage, which conceptually fits with cases of recovery of motor function.

Influence of constrained visual and somatic senses on controlling centre of mass during sit-to-stand

This study aimed to investigate the manner in which healthy individuals execute robust whole body movements despite unstable body structure from the perspective of perception-action coupling. Twelve healthy adults performed sit-to-stand (STS) movements under conditions of constrained visual and somatic senses. During this movement, centre of mass (COM) of the body in the anterior-posterior, upward-downward and right-left directions was computed. The conditions of perceptual constraint were set as vision-restricted, somatosensory-restricted, vision- and somatosensory-restricted, and normal conditions. To evaluate COM control under these perceptual constraints, the variability in position and velocity of COM were assessed. The variabilities in COM velocity in the anterior-posterior and upward-downward directions decreased around the lift-off period only when both vision and somatic senses were constrained, whereas the variability of the COM position in the right-left direction increased under the somatosensory-restricted condition. Our findings suggested that control of COM velocity was enhanced in the major moving directions (anterior and upward directions) around the lift-off period during STS when both modalities of perception with regard to postural orientation were constrained. These motor regulations with perceptual constraints facilitate better adaptation to changes in body and environmental situations in daily life.

Maladaptive change of body representation in the brain after damage to central or peripheral nervous system

Our brain has great flexibility to cope with various changes in the environment. Use-dependent plasticity, a kind of functional plasticity, plays the most important role in this ability to cope. For example, the functional recovery of paretic limb motor movement during post-stroke rehabilitation depends mainly on how much it is used. Patients with hemiparesis, however, tend to gradually disuse the paretic limb because of its motor impairment. Decreased use of the paretic hand then leads to further functional decline brought by use-dependent plasticity. To break this negative loop, body representation, which is the conscious and unconscious information regarding body state stored in the brain, is key for using the paretic limb because it plays an important role in selecting an effector while a motor program is generated. In an attempt to understand body representation in the brain, we reviewed animal and human literature mainly on the alterations of the sensory maps in the primary somatosensory cortex corresponding to the changes in limb usage caused by peripheral or central nervous system damage.

Imitation movement reduces the phantom limb pain caused by the abnormality of body schema

Phantom limb pain is caused by the abnormality of the body schema. It is known that the mirror therapy is one of the most effective ways for reducing the phantom limb pain by using the visual information of the intact limb as the visual feedback of the amputated one, with looking through the mirror. This mirror therapy, however, works only for amputees with single limb amputation, because mirror therapy needs the vision of intact limb. Here, we tried to use the vision of the limb of another person as the visual feedback of the amputated limb by imitation movement and we reports that imitation movement could reduce the phantom limb pain of the amputee with bilateral lower limbs and left upper limb amputation by performing imitation movements.

Clinical utility of diffusion tensor imaging and fibre tractography for evaluating diffuse axonal injury with hemiparesis.

Although diffuse axonal injury (DAI) frequently manifests as cognitive and/or motor disorders, abnormal brain findings are generally undetected by conventional imaging techniques. Here we report the case of a patient with DAI and hemiparesis. Although conventional MRI revealed no abnormalities, diffusion tensor imaging (DTI) and fibre tractography (FT) revealed the lesion speculated to be responsible for hemiparesis. A 37-year-old woman fell down the stairs, sustaining a traumatic injury to the head. Subsequently, she presented with mild cognitive disorders and left hemiparesis. DTI fractional anisotropy revealed changes in the right cerebral peduncle, the right posterior limb of the internal capsule, and the right corona radiata when compared with the corresponding structures observed on the patients left side and in healthy controls. On FT evaluation, the right corticospinal tract (CST) was poorly visualised as compared with the left CST as well as the CST in healthy controls. These findings were considered as evidence that the patients left hemiparesis stemmed from DAI-induced axonal damage in the right CST. Thus, DTI and FT represent useful techniques for the evaluation of patients with DAI and motor disorders.

Association between white matter hyperintensity and lacunar infarction on MRI and subitem scores of the Japanese version of mini-mental state examination for testing cognitive decline: the Ohasama study.

We assessed whether subitem scores on the Mini-Mental State Examination (MMSE) associated independently with cerebral white matter hyperintensity (WMH) and lacunar infarction (LI). Magnetic resonance imaging (MRI) and neuropsychological evaluation (MMSE) were performed in 1008 elderly individuals from the Ohasama Study (348 men, 660 women [65.5%]; age 68.0 ± 6.0 [mean ± SD] years; MMSE score, 26.5 ± 2.9). The relationships between MRI findings and MMSE subitem scores were analyzed by logistic regression. Significant associations were observed between the MMSE subitems “Orientation to place” and WMH, and “Copy a figure” and LI. Pathological changes were detected by brain MRI associated with a decrease in cognitive function in healthy elderly individuals.

Time-dependent decline of body-specific attention to the paretic limb in chronic stroke patients

Objective To examine whether reduced body-specific attention to a paretic limb is found in chronic stroke patients in a time-dependent manner. Methods Twenty-one patients with chronic hemiparesis (10 left and 11 right hemiparesis) after subcortical stroke and 18 age-matched healthy controls were recruited in this study. Standard neuropsychological examinations showed no clear evidence of spatial neglect in any patient. In order to quantitatively measure spatial attention to the paretic hand, a visual detection task for detecting a target appearing on the surface of either a paretic or dummy hand was used. This task can measure the body facilitation effect, which makes faster detection of a target on the body compared with one far from the body. Results In stroke patients, there was no difference in the reaction time for a visual target between the paretic and the dummy hands, while the healthy participants showed faster detection for the visual target on the real hand than on the dummy one. The index of the body facilitation effect, subtracting the reaction time for the target-on-paretic hand from that for the target-on-dummy one, was correlated with the duration since onset and with finger function test on the Stroke Impairment Assessment Set. Conclusions The reduction of the body facilitation effect in the paretic limb suggests the decline of body-specific attention to the paretic one in patients with chronic hemiparesis. This decline of body-specific attention, leading to neglect for the paretic limb, will be one of the most serious problems for rehabilitation based on use-dependent plasticity.

Effect of Cathodal Transcranial Direct Current Stimulation on a Child with Involuntary Movement after Hypoxic Encephalopathy

The aim of the study was to investigate the effect of cathodal transcranial direct current stimulation to the supplementary motor area to inhibit involuntary movements of a child. An 8-year-old boy who developed hypoxic encephalopathy after asphyxia at the age of 2 had difficulty in remaining standing without support because of involuntary movements. He was instructed to remain standing with his plastic ankle-foot orthosis for 10 s at three time points by leaning forward with his forearms on a desk. He received cathodal or sham transcranial direct current stimulation to the supplementary motor area at 1 mA for 10 min. Involuntary movements during standing were measured using an accelerometer attached to his forehead. The low-frequency power of involuntary movements during cathodal transcranial direct current stimulation significantly decreased compared with that during sham stimulation. No adverse effects were observed. Involuntary movement reduction by cathodal stimulation to supplementary motor areas suggests that stimulations modulated the corticobasal ganglia motor circuit. Cathodal stimulation to supplementary motor areas may be effective for reducing involuntary movements and may be safely applied to children with movement disorders.