Tetsuo Kida

Differential influences of exercise intensity on information processing in the central nervous system

The influence of exercise intensity on information processing in the central nervous system was investigated using P300 and no-go P300 event-related potentials. Twelve subjects (22–33xa0years) performed a go/no-go reaction time task in a control condition, and again after high-, medium-, and low-intensity pedaling exercises. Compared to the control condition, P300 amplitude decreased after high-intensity pedaling exercise and increased after medium-intensity pedaling exercise. There was no change after low-intensity pedaling exercise. These results suggested that the amount of attentional resources devoted to a given task decreased after high-intensity exercise and increased after medium-intensity exercise. The findings also suggest that changes in P300 amplitude are an inverted U-shaped behavior of differences in exercise intensity. In addition, no-go P300 amplitude showed the same changes as P300 amplitude at different exercise intensities. This indicates that differences in exercise intensity influenced not only the intensity of processing the requirement for a go response, but also processing of the need for a no-go response. It is concluded that differences in exercise intensity influenced information processing in the CNS.

Changes in arousal level by differential exercise intensity.

OBJECTIVEnThe purpose of the present study was to investigate the influence of exercise intensity on arousal level.nnnMETHODSnTwelve 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.nnnRESULTSnCNV 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.nnnCONCLUSIONSnThese 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.nnnSIGNIFICANCEnThe 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.

Passive enhancement of the somatosensory P100 and N140 in an active attention task using deviant alone condition.

OBJECTIVEnWe investigated the changes in the somatosensory P100 and N140 during passive (reading) versus active tasks (counting, button pressing) and oddball (target=20%, standard=80%) versus deviant alone conditions (standards were omitted).nnnMETHODSnNine healthy subjects performed the 3 tasks (reading, counting and button pressing) under two conditions. Standard and target electrical stimuli were presented in a random order to the index or middle fingers of the left hand at a constant 800 ms interstimulus interval in the oddball conditions. In the deviant alone conditions, only target stimuli were presented with the same timing as in the oddball conditions.nnnRESULTSnThe N140 amplitude increased for the deviant alone stimuli compared with the oddball standard and target stimuli regardless of whether the task was passive or active, indicating passive shifts of attention related to temporal infrequency. The P100 amplitude also increased for the deviant alone stimuli compared with the oddball standard and target stimuli in both passive and active tasks, but the enhancement seemed to be even smaller than that of the N140 amplitude.nnnCONCLUSIONSnThe somatosensory N140 passively increased even if subjects tried to attend actively to the stimulus source when the deviant alone condition was used. This change in N140 amplitude may be related to a strong orienting effect against a silent background.nnnSIGNIFICANCEnThe present study provided evidence that the N140 is an indicator of passive attention against a silent background when the deviant alone condition or long interstimulus interval was used.

Effects of a go/nogo task on event-related potentials following somatosensory stimulation

OBJECTIVEnWe investigated the effects of a go/nogo task on event-related potentials (ERPs) evoked by somatosensory stimuli.nnnMETHODSnERPs following electrical stimulation of the second (go stimulus) or fifth (nogo stimulus) left-handed digit were recorded from 9 subjects. The recordings were conducted in 3 conditions: Control, Count and Movement. The subjects were instructed to count the go stimuli silently in Count, and respond to the go stimuli by grasping right hands in Movement. Go and nogo stimuli were presented at an even probability.nnnRESULTSnN140 was recorded in all conditions and P300 in Count and Movement. The mean amplitudes of the nogo stimuli in the interval 140-200 msec and nogo-N140 amplitude were significantly more negative than those of the go stimuli in Count or Movement. Nogo-P300 was larger in amplitude than go-P300 in Movement but not Count. The effect of P300 was applied to Fz and Cz, but not at Pz.nnnCONCLUSIONSnIn the present study, effects of a somatosensory go/nogo task on ERPs were investigated, and our findings were very similar to those of previous studies using visual and auditory go/nogo tasks. Therefore, we suggest that cortical activities relating to go/nogo tasks are not dependent on sensory modalities.nnnSIGNIFICANCEnThe present study showed for the first time the go/nogo effects on somatosensory-evoked ERPs. These effects were similar to those in visual and auditory ERP studies.

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

OBJECTIVEnThe 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.nnnMETHODSnUnder 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.nnnRESULTSnThe 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.nnnCONCLUSIONSnThe 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.nnnSIGNIFICANCEnThe present study may show that the P300 amplitude reflects modality-unspecific resource at more central level, and that the N140 amplitude involves perceptual resource.

Effects of ISI and stimulus probability on event-related go/nogo potentials after somatosensory stimulation

The present study investigated the characteristics of the middle-latency negative potential of event-related potentials (ERPs) using somatosensory go/nogo tasks. We manipulated interstimulus interval (ISI) in Experiment 1 and stimulus probability in Experiment 2 and analyzed the subtracted difference waveform resulting from subtraction of the ERP evoked by the go stimulation from that evoked by the nogo stimulation. In Experiment 1, the peak latency of negativity became significantly longer as the ISI increased, but the peak amplitude was unchanged. The reaction time (RT) was longer with increasing ISI. In Experiment 2, manipulation of the stimulus probability yielded an increase in peak amplitude with decreasing probability of the nogo stimulus, but did not affect the latency. The RT increased as the probability of a nogo stimulus rose. Because manipulation of the ISI and stimulus probability elicited different brain activities, we hypothesized that manipulation of the ISI elicited a delay of the stimulus evaluation process including response inhibition, and that stimulus probability significantly affected the strength of the response inhibition process.

Differential modulation of the short- and long-latency somatosensory evoked potentials in a forewarned reaction time task

OBJECTIVEnWe investigated modulation of the short- and long-latency somatosensory evoked potentials (SEPs) in a forewarned reaction time task.nnnMETHODSnA pair of warning (auditory) and imperative stimuli (somatosensory) was presented with a 2 s interstimulus interval. In movement condition, subjects responded by grip movement with the ipsilateral hand to the somatosensory stimulation when the imperative stimulus was presented. In counting condition, they silently counted the number of imperative stimuli. The SEPs in response to the imperative stimuli were recorded.nnnRESULTSnFrontal N30 and central N60 amplitudes were significantly smaller in the movement than in the counting or rest conditions. None of the short-latency components differed between the counting and rest conditions. In contrast to the short-latency components, P80 was significantly larger in the counting than in the rest condition, and showed a further increase from the counting to the movement condition. The N140 amplitude was significantly larger in the movement than the rest condition, but was not changed between the counting and the rest conditions.nnnCONCLUSIONSnThe attenuation of the frontal N30 and central N60, and the enhancement of the P80 and possibly the N140 resulted from the centrifugal mechanism. The present findings may show the different effects of voluntary movement on the early and subsequent cortical processing of the relevant somatosensory information requiring a behavioral response.nnnSIGNIFICANCEnThe present study demonstrated the differential modulation of short- and long-latency components of SEPs in a forewarned reaction time task.

Changes in the somatosensory N250 and P300 by the variation of reaction time

We investigated the relationship between somatosensory event-related potentials (ERP) and the variation of reaction time (RT). For this purpose, we recorded the ERPs (N250 and P300) in fast- and slow-reaction trials during a somatosensory discrimination task. Strong, standard, and weak target electrical stimuli were randomly delivered to the left median nerve at the wrist with a random interstimulus interval (900–1,100xa0ms). All the subjects were instructed to respond by pressing a button with their right thumb as fast as possible whenever a target stimulus was presented. We divided all the trials into fast- and slow-RT trials and averaged the data. N250 latency tended to be delayed when the RT was slow, but not significantly. P300 latency was delayed significantly when the RT was slow, but to a much lesser extent than the RT delay, so we concluded that the change of RT was not fully determined by the processes reflected by the somatosensory N250 or P300. Furthermore, the larger and earlier P300 in the fast-RT trials implied that when larger amounts of attentional resources were allocated to a given task, the speed of stimulus evaluation somewhat increased and RT was shortened to a great extent. N250 amplitude did not significantly vary in the two RT clusters. In conclusion, the somatosensory N250 reflects active target detection, which is relatively independent of the modulation of the response speed, whereas the somatosensory P300 could change without manipulation of either the stimulus or the response processing demand.

Attenuation of the effect of remote muscle contraction on the soleus H-reflex during plantar flexion

OBJECTIVEnWe investigated to what extent the facilitation of the soleus (Sol) Hoffmann (H-) reflex during a phasic voluntary wrist flexion (Jendrássik maneuver, JM) can be modulated by graded plantar flexion force and conditioning wrist flexion force.nnnMETHODSnThe subjects were asked to perform phasic wrist flexion under a reaction time condition. Sol H-reflex was evoked by stimulating the right tibial nerve at various time intervals (50-400ms) after the Go signal for initiating JM while the ankle was at rest and while plantarflexing. The level of tonic plantar flexion force (isometric contraction of 10, 20 and 30% of maximal EMG) and conditioning wrist flexion (isometric contraction of 30, 50 and 80% of maximum voluntary contraction) during JM was graded systematically.nnnRESULTSnAlthough JM facilitation could be seen 80-120ms after the flexor carpi radialis (FCR) EMG onset even while plantarflexing, the magnitude of JM facilitation under plantar flexion was significantly decreased compared to that at rest. The degree of decrease in JM facilitation did not depend on the level of plantar flexion force. In contrast, the degree of JM facilitation was proportional to the level of wrist flexion force while the ankle was at rest and while plantarflexing, though the amount of JM facilitation significantly decreased while plantarflexing.nnnCONCLUSIONSnJM facilitation of Sol H-reflex is decreased while performing tonic voluntary contraction of the homonymous muscle. The degree of decrease in JM facilitation is independent of the level of homonymous muscle contraction, but depends on the level of remote FCR contraction. In clinical application, when we intend to elicit a maximum stretch reflex by JM, full relaxation of homonymous muscle should be carefully confirmed.nnnSIGNIFICANCEnOur results provide evidence for better understanding of the features of JM and insight into its clinical application.

Load- and cadence-dependent modulation of somatosensory evoked potentials and Soleus H-reflexes during active leg pedaling in humans

Modulation of transmission in group I muscle afferent pathways to the somatosensory cortex and those to the alpha-motoneuron were investigated during active leg pedaling. Cerebral somatosensory evoked potentials (SEPs) and Soleus (Sol) H-reflexes following posterior tibial nerve stimulation were recorded at four different pedaling phases. The subjects were asked to perform pedaling at three different cadences (30, 45 and 60 rpm with 0.5 kp, cadence task; C-task) and with three different workloads (at 45 rpm with 0.0, 0.5 and 1.0 kp, load task; L-task). In both C- and L-tasks, Sol H-reflexes were modulated in a phase-dependent manner, showing an increase in the power phase and a decrease in the recovery phase. In contrast, the early SEP (P30-N40) components were modulated in a phase-dependent manner when the cadence and load were low. When focusing on the power phases, significant cadence- and load-dependent modulations of the P30-N40 were found, and inversely graded with the cadence and load. The H-reflex was found to be significantly decreased at the highest cadence, i.e., cadence-dependent modulation. In contrast, the H-reflex during the L-task was found to be proportional to the load. The correlation analysis between the size of H-reflex and the amount of background (BG) electromyographic (EMG) activity demonstrated that the H-reflex in the power phase did not depend on the BG EMG in either C- or L-task. These findings suggested that transmission of muscle afferents along the ascending pathways to the cerebral cortex and the spinal cord is independently controlled in accordance with the biomechanical constraints of active pedaling.