Kazuo Kuroiwa

Changes in arousal level by differential exercise intensity.

OBJECTIVE The purpose of the present study was to investigate the influence of exercise intensity on arousal level. METHODS Twelve subjects (22-33 years) performed a S1-S2 reaction time task consisting of warning stimulus (S1) and imperative stimulus (S2) in a control condition, and again after low, medium, and high intensity pedaling exercises. During this task, contingent negative variation (CNV) and spontaneous electroencephalogram before S1 were measured as indicators for arousal level. RESULTS CNV amplitude after high intensity pedaling exercise was significantly smaller than after medium pedaling exercise. Compared to the control condition, relative power value of alpha waves increased after the high intensity exercise. CONCLUSIONS These results suggested that arousal level was reduced after high intensity exercise and reached a state near optimal level after medium intensity exercise. The findings also suggested that changes in CNV amplitude by differences in exercise intensity followed an inverted-U shaped dose response curve. SIGNIFICANCE The present study supported the view that CNV amplitude and arousal level followed an inverted-U relationship. It is concluded that differences in exercise intensity influenced arousal level.

Resource allocation and somatosensory P300 amplitude during dual task: effects of tracking speed and predictability of tracking direction

OBJECTIVE The amount of attentional resources allocated to a task is determined by the intrinsic demands, also denoted as task load or difficulty of the task. Effects of resource allocation on the somatosensory N140 and P300 were investigated in an inter-modal situation using a dual-task methodology. METHODS Under a dual-task condition, subjects concurrently performed a visuomotor tracking task and a somatosensory oddball task, while they performed just the oddball task under an oddball-only condition. In the tracking task, the subjects tracked the target line, which was presented on an oscilloscope and automatically moved, with the line which represented their own force generated by grip movement with the left hand. Tracking speed (experiment 1) and tracking predictability (experiment 2) were manipulated to vary task difficulty. N140, P300, and reaction time (RT) in the oddball task and tracking accuracy in the tracking task were measured. RESULTS The P300 and N140 amplitudes were reduced in the dual-task condition compared to those in the oddball-only condition. The fastest tracking speed produced lower tracking accuracy and later RT. However, the tracking speed did not affect the P300 or N140 amplitudes. In contrast, the P300 amplitude was smaller when the change in tracking direction was unpredictable than when it was predictable, without any differences in tracking accuracy or RT, N140. CONCLUSIONS The differences in behaviors among N140, P300, and RT following manipulation of task difficulty support the multiple-resource hypothesis, which defines functionally separate pools of resources. SIGNIFICANCE The present study may show that the P300 amplitude reflects modality-unspecific resource at more central level, and that the N140 amplitude involves perceptual resource.

Somatosensory Event-Related Potentials (ERPS) Associated with Stopping Ongoing Movement

The somatosensory event-related potentials (ERPs) associated with stopping ongoing movement and increasing muscular tension were examined. 14 healthy right-handed volunteers, 10 men and 4 women (21–29 years old, M age ± SD, 24.1 ± 12.5 yr.) performed a stop/increase reaction task. They were requested to perform an elbow extension movement with the right arm and to maintain 20% of the maximum voluntary contraction forces (MVC) before the electrical stimuli were delivered to either the left index finger or the left little finger. They executed one of two movements from the sustained contraction state: they had to stop the muscular tension following the left little finger stimulus or increase the muscular tension from 20% to 40% of the maximum voluntary contraction forces following the left index finger stimulus. The reaction time and somatosensory sequence P100-N140-P300 components of event-related potentials were recorded for each electrical stimulus, respectively. The reaction time was longer to the increase reaction condition than to the stop reaction condition. Neither P100 nor N140 components showed significant differences between stop and increase reaction conditions. The P300 to the stop reaction condition was of greater amplitude and latency than those of the increase reaction condition. These results suggest that stopping the ongoing movement processing requires a longer stimulus evaluation time and is more demanding than increasing reaction processing.