The interactive effects of exercise intensity and physical activity level on the brain and cognition of young adults were investigated using the electromyographic reaction time (EMG-RT), the P3, and the NoGo P3, as well as the contingent negative variation (CNV) of event-related brain potentials. Participants (n＝26 : 24.0 ± 0.7 years) were divided on the basis of their regular physical activity level into active and inactive groups. Then, they performed a Go/NoGo reaction time task in the no exercise, control condition ; as well as after light, moderate, and hard cycling exercises. Results indicated that increases in P3 and NoGo P3 amplitude following moderate exercise were larger in the inactive group, suggesting that inactive individuals were more sensitive to exercise intensity than active individuals. Active individuals might be better able to sustain their attention during the Go/NoGo reaction time task, despite the exercise intensity. These findings are suggestive of a differential effect of exercise intensity on cognitive function that might be dependent on the level of regular physical activity. The effects of exercise intensity on EMG-RTs were observed across groups. However, the P3 latency was not affected by exercise intensity. These contradictory results are possible related to the nature of the cognitive task, such as its difficulty. Moreover, increases in CNV amplitudes following moderate exercise were larger than in other exercise conditions across groups, suggesting that motor preparation process is also facilitated by moderate, acute exercise. These findings provide additional evidence for the beneficial effects of acute aerobic exercise on the brain and cognition of young adults.

We evaluated motor unit (MU) fatigue in the first dorsal interosseous muscle (FDI) using the collision principle. Eight healthy men exerted 70% (short-duration fatigue task: SDF task) and 30% (long-duration fatigue task: LDF task) maximum voluntary contraction of isometric abductions in the left FDI until exhausted. Before and after voluntary contractions, the ulnar nerve was stimulated at the wrist and elbow with supramaximal intensity, and a pair of M-waves was obtained. Fatiguerelated changes were studied in mean power frequency (MPF), averaged rectified value (ARV) calculated from surface EMG, and motor nerve conduction velocity (MCV) and distribution of motor nerve conduction velocity (DMCV) calculated from M-waves. The MPF of voluntary EMG decreased, whereas ARV increased significantly during SDF and LDF tasks, indicating fatigue had developed in the FDI. Endurance was significantly shorter in the SDF task than in the LDF task (p<0.01), whereas differences between tasks were not seen in MPF and ARV changes. Tasks did not affect MCV, but lower components in DMCV increased for both tasks. Increased lower components were larger in the LDF task than in the SDF task. The shift in DMCV indicated that fatigued MUs stopped activity and enduring MUs, which had lower axon conduction velocity, were activated selectively. These results suggest that the collision principle is applicable in evaluating motor unit fatigability.

We studied whether exercise fatigue affects somatosensorv input using somatosensory evoked potential (SEP) . Sixteen subjects performed intermittent grip strength exercises with muscle fatigue while ignoring electrical stimulation given to an elbow. We induced SEP in the exercise task (during contraction) in every stage (first stage, middle stage and final stage) . In addition, we induced SEP in the exercise task during relaxation in the first stage and final stage. As a result, the early component amplitude of SEP decreased with the progress of exercise (manifestation of muscle fatigue) during contraction and relaxation. Our findings suggested that somatosensory input decreased with the manifestation of muscle fatigue. Somatosensory input is necessary for control of voluntary movement. Therefore, we speculate that these factors play a role in decreased performance of athletes competing in long-duration events.

The purpose of this study was to examine how S-R compatibility affected P 300, the stimulusevaluation process and response process. The P 300 component is thought to reflect information processing of stimuli. Previous studies used visual stimuli. In this study, we measured S-R compatibility effects on EMG-RT and P 300 using electrical somatosensory stimuli. Subjects performed the oddball task (Task 1) and the four-choice stimuli response task (Task 2) . They were presented electrical stimuli through ring electrodes on the index and little fingers of both hands and instructed to respond quickly to stimuli. S-R compatibility was decided by position of the stimuli. EMG-RT and P 300 latency for compatible and incompatible conditions were analyzed.
For ERP analysis, data of subjects who reacted faster to compatibility ware used. Neither P 300 latency nor amplitude differed significantly between compatibility and incompatibility in Tasks 1 and 2, but for Task 2, latency tended to be prolonged by incompatibility. Therefore, it is thought that S-R compatibility mainly has an effect on response processing. However, judging from the tendency of P 300 latency to be prolonged by incompatibility for Task 2, it was considered that there is the possibility that S-R compatibility influenced P 300 latency, even if using a somatosensory stimulus.

The mechanism of the latent reaction time in task completion in elderly men was investigated by comparing the reaction time (RT), EMG-RT and motor time (MT) in young and elderly men. The motor performance was recorded as task completion through as a WS-RS, simple reaction or a choice reaction for each movement using a handgrip and switch.
In this study, we found that the RT and EMG-RT of elderly men in all movements of WS-RS and choice reaction tasks were significantly longer than those of young men, especially in the choice reaction tasks were striking. Moreover, the MT of elderly men in all tasks was significantly longer than those of young men.
These findings suggest that the latent RT and EMG-RT in a choice reaction task may be due to relayed information processing through as the discrimination and cognition functions in the brain, and that it may be also influenced by the mechanism of the latent reaction time of task completion in elderly men.

The somatosensory evoked potential (SEP) is attenuated (gating) and the spinal motoneuron pool is facilitated before and during movement. However, the relationship between these changes has not been elucidated. In the present study, the SEP and the evoked electromyogram were simultaneously recorded during a discriminative reaction task in seven healthy subjects. Electrical stimulation applied to the posterior tibial nerve in the popliteal fossa was used as a response signal. The experimental condition were: 1) full relaxation and no response to either right or left stimulation (Control) ; 2) no response to right stimulation and quick contraction of right ankle with left stimulation (L-R) ; 3) no response to left stimulation and quick contraction of right ankle with right stimulation (R-R) . Right and left legs were randomly stimulated under each condition. The H-response gains of the right leg with movement were significantly facilitated compared to the left leg without movement in L-R and R-R conditions. The results indicated that movement enhanced the motoneuron excitability regardless of sensory concentration. In the L-R condition, N 40 at Cz evoked by left operative stimulation that produced right leg movement was significantly increased. However, in the R-R condition, it was significantly attenuated when it was recorded by right operative stimulation that produced right leg movement. These results indicated that concentration on the operative stimulation enhanced the N 40 gain and it reflected the concentration on sensory information, but simultaneously induced the movement, and its gain was strongly controlled by the motor system.

We examined here, changes in event-related potentials (ERPs) in eighteen children from 7 to 12 years and twelve adults. In addition to ERPs, we examined changes of EMG-RT. Subjects performed an auditory target discrimination task, in which 1000 Hz tones (target) and 2000 Hz tones (standard) were randomly presented with probabilities of 0.2 and 0.8.
We found P300 as most consistent component of ERPs since childhood. P300 latency and EMG-RT in children was significantly prolonged than in adults (p<0.01) . P300 amplitude in children was significantly larger than in adults (p<0.05) . We concluded that both stimulus evaluation time and response selection time in children are more prolonged than that in adults, although ERPs is confirmed in children.

Electrophysiologic effects of physical exercise were investigated by comparing a training group and non-training group. ERPs were recorded by oddball paradigm using auditory stimuli as well as count and reaction tasks. EMG-RT was recorded during the reaction task. No reliable exercise effects on N100 amplitudes or latencies were observed. Concerning P300 amplitudes, no significant difference between the training group and non-training group was seen although P300 latencies of the training group were significantly shorter than those of the non-training group in the count task. Moreover, EMG-RT of the training group was significantly shorter than that of the non-training group.
These findings suggest that the long-term physical exercise improved the efficiency of informa-tion processing and superior cognitive function in the brain.

The purpose of this study was to investigate the effect of the sleep deprivation for central information processing. Therefore we examined the changes in the amplitude and the latency of P300 event-related potentials (ERPs) before and after sleep deprivation in eight subjects. In addition to P300, we examined the power spectral changes of the EEG and the R-R intervals at rest before ERP measurements. The subjects performed an auditory target discrimination task and were instructed to keep mental count of each target stimulus. Then 2000 Hz tones (target) and 1000 Hz tones (nontarget) were randomly presented with probabilities of 0.2 and 0.8.
P300 latency at Fz, Cz, C3 and C4 was significantly prolonged after sleep deprivation (p<0.05) . P300 amplitude at Cz after sleep deprivation was significantly smaller than before sleep deprivation (p<0.05) . Alpha 1 power (8-10 Hz) at Cz on EEG was significantly decreased after sleep deprivation, but no other bands changed on EEG. The R-R interval was also significantly extended after sleep deprivation. We concluded that both central information processing and the autonomic nervous system may be influenced by sleep deprivation.

This study was carried out to investigate the influence of pre-movement tonic contraction on the Contingent Negative Variation (CNV) and Flexor Carpi Radialis (FCR) H reflex between the warning (WS) and response signal (RS) (foreperiod : FP) . Two levels of contraction were designed and the accompanying FCR Electromyography (EMG) was directly returned to the subject to sustain constant contraction. The subjects were 10 normal volunteers. Either small or middle (7.9±5.6% or 16.0±6.3% of the standard FCR EMG) contraction was sustained and the isometric wrist flexion movement was performed as quickly as possible following the RS.
EMG Reaction time (RT) in the small contracting condition was shorter than that in the resting condition (nothing performed during the foreperiod) in almost all subjects, but in the middle contracting condition EMG RT was not similar. The CNV amplitude for the late period of the FP, which was considered to be related to the motor preparation, was larger in the middle contracting condition than in the resting condition, although the small contracting condition was similar to the resting condition. The H reflex amplitude for the late period of the FP tended to be smaller than the control level in the small and middle contracting conditions, but it was not significant. However, in over half of the subjects, whose CNV amplitude for the late period of the FP increased linearly depending on the conditions, the H reflex amplitude was smaller than the control level in both contracting conditions, but it was not linear. These results indicate that the modulation of the EMG RT was not directly associated with the CNV or H reflex amplitudes for the late period of the FP, and a functional difference in the set for the RS between the spinal and the upper level of the central nervous system was present.