Minoru Toyokura

Relation of bimanual coordination to activation in the sensorimotor cortex and supplementary motor area: Analysis using functional magnetic resonance imaging

The aim of this study was to analyze how functional activation in the supplementary motor area (SMA) and sensorimotor cortex (SMC) is related to bimanual coordination using functional magnetic resonance imaging. Subjects included 24 healthy volunteers, 15 of whom were right-handed and 9 left-handed. Three kinds of activation tasks, all of which required the repetitive closing and opening of a fist, were performed: unimanual movement of the nonpreferred hand (task A); simultaneous, agonistic movement of both hands (task B); simultaneous, antagonistic movement of both hands (task C). The SMA activation during task C was more pronounced than that during the other two tasks for right and left handers. The results suggested that the activation of the SMA, at least during a simple motion used in the present study, was little influenced by whether the motion was unimanual or bimanual but instead how the bimanual motion was composed of the motion element of a single hand. The SMC activation during task C was significantly larger than that during task B, whereas hemispheric differences in the activation were not found. This indicated that the complexity of the bimanual movement also affected the SMC activation.

Activation of Pre–Supplementary Motor Area (SMA) and SMA Proper During Unimanual and Bimanual Complex Sequences: An Analysis Using Functional Magnetic Resonance Imaging

Several functional imaging studies have shown that the extent of activation and percentage change in cerebral blood flow in the supplementary motor area (SMA) during a bimanual mirror performance of a simple repetitive movement are almost identical to those during a unimanual movement. The aim of this study was to investigate whether this finding was also applicable to a more complex movement. Eight right‐handed, healthy volunteers performed unimanually (with their right and left hands) and bimanually (in a mirror fashion) thumb‐finger opposition in a nonconsecutive order (index‐middle‐index‐ring‐index‐little‐index‐middle… fingers). The SMA proper was more activated during the bimanual movement than the unimanual movement with either hand. This is in accordance with the hypothesis that bimanual movement, even in a mirror fashion, is more difficult than unimanual movement when the task is complex but not when the task is simple. Pre‐SMA was inconsistently activated. The results suggest that the SMA proper plays an active role in executive processing during bimanual mirror performance of complex movements.

Waveform and habituation of sympathetic skin response

The aim of this study was to investigate the relation of sympathetic skin response (SSR) waveform variation to latency, amplitude, and habituation. Twenty SSRs were recorded from the palm skins of 50 normal subjects by electrical stimulations. Reproducibility of SSR waveforms was also evaluated (n = 35). Waveforms were classified as one of two types, namely, the P type, in which the positive component was larger than the negative, and the N type, in which the negative component was larger than the positive. During successive stimulations, 14 of the 50 subjects had only P type waveforms (P pattern), 9 others only the N type (N pattern), and the remaining 27 both the P and N types (M pattern). The P pattern had a larger amplitude and shorter latency than the N pattern. Twenty-seven of the 35 subjects had the same SSR pattern in two tests conducted on different days. Habituation with time was more pronounced for the M pattern than for the other two patterns. It was suggested that changes in SSR waveform during successive stimulations reflected habituation. Most subjects with the M pattern had a distinct attribute in the development of habituation.

Sympathetic skin responses: the influence of electrical stimulus intensity and habituation on the waveform

Repeated stimulation of the sympathetic skin response (SSR) causes habituation. The aim of this study was to determine the effects of electrical stimulus intensity on SSR in 40 healthy controls (mean age±SD, 28.0±6.7 years). Electrical stimuli at three intensities (5, 15 and 30 mA) were applied to the median nerve at the wrist in four consecutive sessions, after which a magnetic stimulus was applied to the neck. SSR were classified according to the proportion of positive (P) and negative (N) waveform components.Twentyfour subjects had both P and N waveforms. In the first session, 75% of these subjects had a P waveform, indicative of a greater SSR, in response to the 30 mA shock. In the progressive sessions, the SSR waveform was predominately negative (N waveform, session 2, 65%; session 3, 83%; session 4, 75% in response to 30 mA shock), indicating that the SSR was weaker as a result of habituation. There was no clear relationship between stimulus intensity and waveform type, indicating that SSR waveforms are more strongly influenced by habituation than stimulus intensity. However, there was a directly proportional relationship between stimulus intensity and amplitude of the SSR wave (F=70.9, P<0.0001, two-way repeated measure ANOVA), be it positive or negative. The relationship between stimulus intensity and amplitude persisted, even after habituation. Suddenly switching to a magnetic stimulus reverted the SSR wave back to positive (80%), indicating that habituation was rapidly reversible if stimulation of the SSR is altered.

Waveform variation and size of sympathetic skin response: regional difference between the sole and palm recordings

OBJECTIVE The aim of this study was to investigate the regional difference in sympathetic skin response (SSR). The influence of SSR waveform from sole skin (S-SSR) on latency, amplitude, and habituation was also studied. METHODS Twenty SSRs were analyzed in 41 normal subjects. Waveforms were classified as either the P type, in which the positive component was larger than the negative one, or the N type, in which the negative component was larger the positive one. The occurrence patterns of these two waveform types were classified into three kinds, i.e. P, N, and M patterns. In the P or N pattern all the SSRs were of the P or N type. The M pattern had both P and N types during consecutive recordings. RESULTS In the S-SSR, the P pattern had a higher amplitude and shorter latency than the N pattern, and habituation was most pronounced in the M pattern. These were compatible with previously reported findings in SSR from palm (P-SSR). The waveform patterns were not always consistent between P- and S-SSRs. The maximum S-SSR and P-SSR were not simultaneously obtained in nearly half of the subjects. CONCLUSIONS The size and waveforms of SSR were modified not only by the condition of the central component, but also the peripheral component of the reflex and the sweat gland.

Influence of stimulus intensity on waveform of sympathetic skin response evoked by magnetic stimulation

OBJECTIVE The aim of this study was to investigate the influence of stimulus intensity on the waveform of sympathetic skin response (SSR). The origin of the SSR waveform was discussed. METHODS A total of 12 SSRs from palm skin were analyzed in 40 normal subjects. SSR was evoked by magnetic stimulation to the neck at 3 different intensities (10, 35, and 70% of the maximum output). The 3 stimuli were repeatedly applied in 4 separate sets. Waveforms were classified as either the P type, in which the positive component was larger than the negative one, or the N type, in which the negative component was larger than the positive one. Amplitude values of peak-to-peak, the first negative (N1), and subsequent positive (P1) components were compared among the 12 responses. RESULTS When the stimulation was increased, the SSR size became larger. The P type SSR was most frequently found in the maximum stimulation. Strong stimulation generally produced a large P1. Only the N type SSR exhibited a large N1 response to the maximum stimulation. There was a significant, negative correlation between N1 peak duration (difference between the SSR onset and N1 peak latencies) and P1 amplitude. CONCLUSIONS These results suggested that strong responses probably produced a P type SSR with a large P1 component. In this condition, a rapid change of potential from negative to positive prevented any correlation between N1 amplitude and the magnitude of the response. In the N type SSR, however, a large N1 was associated with a strong response. These findings can be explained by a newly presented theory on the neurophysiological origin of the negative and positive components, based on a model of equivalent current dipole dependent on the Na+ concentration gradient. SIGNIFICANCE The present study provided some suggestions on the neurophysiological mechanism of SSR waveform.

F wave duration in mild S1 radiculopathy: comparison between the affected and unaffected sides

OBJECTIVES The aim of this study was to investigate the F wave duration (Fdur) of the tibial nerve in mild S1 radiculopathy. We evaluated the difference in this parameter between the affected and unaffected sides, and discussed the clinical significance of this difference. METHODS Bilateral tibial F waves were obtained from 46 normal subjects (control group) and 27 patients with L5/S1 intervertebral disc herniation (patient group). Minimum latency of F wave (Fmin) and Fdur were analyzed. RESULTS Fmin and Fmin corrected by the subjects height (Fmin/H) were both significantly longer on the affected side than on the unaffected side and in the normal group, but the incidence of abnormality was very low for both parameters. Even patient showing normal Fmin or Fmin/H sometimes exhibited Fdur values prolonged beyond the reference range. Judgment of abnormal Fdur based on the difference between the two sides was the most sensitive method for detecting the root injury. No patients showed decreased Fdur. There was no significant difference between the two groups in the amplitude of compound muscle action potential of the abductor hallucis. CONCLUSIONS Our study suggested that evaluation of the difference in Fdur between the two sides was a valuable means of decreasing false-negative results in F wave study in mild S1 radiculopathy cases.

Within-subject consistency of sympathetic-skin-response waveform across different modalities of stimulation.

This study was conducted to investigate the intra-subject consistency of the waveform type and the size of the sympathetic skin response (SSR) evoked by different modalities of stimulation. Thirty-eight normal volunteers were enrolled as subjects. SSRs were obtained using three different modalities of stimulations: auditory (a-SSR), electrical (e-SSR), and magnetic (m-SSR). Four stimuli of each modality were applied. The waveforms were classified into two types, P (positive component larger the than negative component) and N (vice versa). P-type waveforms were less frequent in the a-SSR than in the e- and m-SSR. The occurrence of the respective waveforms and the values of maximum amplitudes were significantly correlated among the SSRs evoked by different types of stimulation. Judging from these results, the SSR waveforms and size seemed to be consistent in individuals. The results also suggested that endogenous factors in an individual related to the development of SSRs e.g., individuals emotional state, susceptibility to the surprise effect, and anatomical characteristic were important determinants of the SSR waveforms and maximum amplitude.

Paradoxical shortening of sympathetic skin response latency at distal recording sites.

OBJECTIVE The purpose of this study was to investigate and to discuss the neurophysiological mechanism of paradoxical shortening of the sympathetic skin response (SSR) latency at distal recording sites. METHODS The latency and peak-to-peak amplitude of SSRs evoked by magnetic stimuli were analyzed. Eight active electrodes were placed on the palmar (anterior) and dorsal (posterior) sides of the hand (forearm) proximal to the distal arrangement. RESULTS SSRs from two palm sites had significantly shorter latencies and larger amplitudes than the SSRs at the other six sites, including the proximal sites of the forearm. CONCLUSIONS This finding indicated that the SSR latency at different sites was not linearly prolonged as the distance of the recording sites from the proximal to distal areas increased. The paradoxical shortening of the latency and the large amplitude of the SSR from the palm can be explained by a recent model of the equivalent current dipole caused by the Na+ concentration gradient. The high density of sweat glands in the palm possibly produced the present findings. SIGNIFICANCE We should carefully interpret the sudomotor conduction velocity derived from latency difference between two sites, especially for thermal and emotional sweating.

Intermanual difference in the Japanese Trail Making Test and its mirror version: intra-subject comparison of the task-completion time, cognitive time, and motor time

Purposes: To investigate intermanual differences in the performance of the Japanese Trail Making Test (JTMT) using an intra-subject comparison, and to investigate how the cognitive and motor times spent in performing the task were related with the total completion time. Methods: All subjects performed both parts A and B of the following three tasks: JTMT with the right hand (R); JTMT with the left hand (L); and a mirror version of the JTMT with the left hand (M). The order in which these three tasks were performed (RLM, RML, LRM, LMR, MRL, and MLR) was randomly determined. An interval of 4 weeks was scheduled between each examination. In addition to the completion time, we measured ‘motor time’, a sum of the times for drawing lines to connect the targets, and ‘cognitive time’, a time obtained by subtracting the motor time from the completion time. Results: The task-completion time was more strongly correlated with the cognitive time than with the motor time. The order of the task performance did not influence the task-completion time. A learning effect was found only between the first and second examinations of part A. The cognitive time for the second and third performances of part A were significantly shorter than that for the first task, whereas the motor time remained unchanged. No intermanual differences in the performance were found in any comparisons. Conclusions: The non-dominant hand can be used as an alternative hand in the JTMT, and it can be expected to perform comparably to the dominant hand. These findings are consistent with the finding previously obtained by inter-subject comparison. The lack of any significant intermanual difference can be explained by that the total completion time is less influenced by the motor time than by the cognitive time.