Biomedical subjects

Toshiaki Wasaka

Publications and source records attributed to Toshiaki Wasaka.

28 records · Page 2Linked to original sources

PubMed2004

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

OBJECTIVE: We investigated modulation of the short- and long-latency somatosensory evoked potentials (SEPs) in a forewarned reaction time task. METHODS: A 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. RESULTS: Frontal 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. CONCLUSIONS: The 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. SIGNIFICANCE: The present study demonstrated the differential modulation of short- and long-latency components of SEPs in a forewarned reaction time task.

Acoustic Stimulation↗

PubMed2004

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.

Adult↗

PubMed2004

Differential modulation of temporal and frontal components of the somatosensory N140 and the effect of interstimulus interval in a selective attention task.

The modulation of the somatosensory N140 was examined in a selective attention task where a control condition was applied and the interstimulus interval (ISI) was varied. Electrical stimuli were randomly presented to the left index (p=0.4) and middle fingers (p=0.1), and right index (p=0.4) and middle fingers (p=0.1). In the attend-right condition, subjects were instructed to count silently the number of infrequent target stimuli presented to the right middle finger, and to the left middle finger in the attend-left condition. They had no task in the control condition. Each condition was performed with two different sets of ISI (mean 400 vs. 800 ms). The somatosensory N140 elicited by frequent standard stimuli was analyzed. The N140 amplitude was larger for the attended ERP compared to the control and unattended ERPs. This attention effect was more marked at the frontal electrodes compared to the temporal electrodes contralateral to the stimulation side. Furthermore, the attention effect at the frontal electrode was larger when the ISI was 800 ms than when it was 400 ms. The N140 amplitude did not differ between the control and unattended ERPs, which might show that a small processing negativity (PN) occurred during the control condition or difference in vigilance level between them. In conclusion, the early lateral ("temporal") and late midline ("frontal") components of the N1 (N140) show different behavior, and thus may have different functional significance. Enhancement of the attention effect at the frontal electrode in the longer ISI condition supports the hypothesis that it is related to stronger, voluntary maintenance of the attentional trace.

Adult↗

PubMed2004

Movements modulate cortical activities evoked by noxious stimulation.

To evaluate the effects of movement on cortical activities evoked by noxious stimulation, we recorded magnetoencephalography following noxious YAG laser stimulation applied to the dorsum of the left hand in normal volunteers. Results of the present study can be summarized as follows: (1) active movement of the hand ipsilateral to the side of noxious stimulation resulted in significant attenuation of both primary and secondary somatosensory cortices (SI and SII) in the hemisphere contralateral to the stimulated hand (cSI and cSII). Activity in the hemisphere ipsilateral to the side of stimulation (iSII) was not affected. (2) Active movement of the hand contralateral to the side of noxious stimulation resulted in significant attenuation of cSII. Activity in cSI and iSII was not affected. (3) Passive movement of the hand ipsilateral to the side of noxious stimulation resulted in significant attenuation of cSI. Activity in cSII and iSII was not affected. (4) Visual analogue scale (VAS) changes showed a similar pattern to the amplitude changes of cSII. These results suggest that activities in three regions are modulated by movements differently. Inhibition in cSI was considered to be mainly due to an interaction in SI by the signals ascending from the stimulated and movement hand. Inhibition in cSII was considered to be mainly due to particular brain activities relating to motor execution and/or movement execution associated with a specific attention effect. In addition, since VAS changes showed a similar relationship with the amplitude changes of cSII, cSII may play a role in pain perception.

Adult↗

PubMed2003

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 (900-1,100 ms). 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.

Adult↗

PubMed2003

Somatosensory N250 and P300 during discrimination tasks.

We investigated the event-related potentials (N250 and P300) during three kinds of somatosensory discrimination tasks (oddball task). Strong (standard: 90%) and weak (deviant: 10%) electrical stimuli were randomly delivered to the right median nerve at the wrist with a 500-ms constant interstimulus interval. In a passive situation, subjects read a self-selected book, ignoring all stimuli (ignore condition). One of the active situations was a mental counting task (count condition), and another required pressing a button to deviant stimuli as quickly as possible (motor response condition). The N250-P300 complex was elicited by deviant stimuli in the active-attended situations, but not found in the ignore condition. The N250 peak amplitude was unchanged between the count and motor response conditions whereas P300 changed. In addition, the N250 latency significantly correlated with the reaction time, but the P300 latency did not. These results indicate that the somatosensory N250 reflects an attentive process which is related to the temporal aspect of behavioral response.

Adult↗

PubMed2003

Gating of somatosensory evoked magnetic fields during the preparatory period of self-initiated finger movement.

The temporal change in somatosensory evoked magnetic fields (SEFs) in the preparatory period of self-initiated voluntary movement was investigated. The SEF following stimulation of the right median nerve was recorded, using a 204-channel whole-head MEG system, in nine healthy subjects during a self-initiated extension of the right index finger every 5 to 7 s. The preparatory period before finger movement was divided into six subperiods, and the MEG signals following the stimulation in each subperiod were averaged separately. SEFs were also recorded in the resting state. The ECD strengths for N20m and P60m were not significantly changed in any subperiod before movement compared with those in the resting state. The ECD strength for P30m was significantly smaller 500 ms or less before movement than during the resting state and 1,500 ms or less before movement compared to that during the period from 3,000 to 4,000 ms before movement. Thus, we confirmed that the SEF components were attenuated even during a period of self-initiated voluntary movement. The modulation started at least 1,500 ms before movement and was greater for the P30m than the N20m component. These findings suggested that motor-associated cortices attenuated SEF components by a centrifugal gating process.

Adult↗

PubMed2003

Mechanisms of differences in gating effects on short-and long-latency somatosensory evoked potentials relating to movement.

We investigated the mechanisms underlying the differences in gating effects on short- and long-latency somatosensory evoked potentials (SEPs) relating to movement. SEPs were recorded in normal subjects for 6 different tasks in Experiment 1: Control, Movement, Distraction, Attention, Movement during Distraction and Movement during Attention, and for 4 different tasks in Experiment 2: Control, Passive Movement, Contralateral Movement and Movement Imagery. The amplitudes of short-latency SEPs were significantly reduced by active and passive movement of the stimulated hand, but long-latency SEPs (N140-P200) were significantly enhanced by active movement of the stimulated hand. Attention, Distraction, Contralateral Movement and Movement Imagery did not affect the amplitudes of SEPs. The degree of enhancement of long-latency SEPs by active Movement was greater than that by active movement with Attention or Distraction. Gating effects on long-latency SEPs were different from those on short-latency SEPs. Since this effect was not related to Attention/Distraction, Passive Movement, Movement Imagery or Movement of another site, it is probably due to specific centrifugal effects, which are different from more direct gating effects on short-latency components. This study showed the difference in gating effects on somatosensory perception depending on time periods following stimulation, which may indicate an interaction between motor and somatosensory cortex.

Adult↗

PubMed2003

Pain processing within the primary somatosensory cortex in humans.

To investigate the processing of noxious stimuli within the primary somatosensory cortex (SI), we recorded magnetoencephalography following noxious epidermal electrical stimulation (ES) and innocuous transcutaneous electrical stimulation (TS) applied to the dorsum of the left hand. TS activated two sources sequentially within SI: one in the posterior bank of the central sulcus and another in the crown of the postcentral gyrus, corresponding to Brodmann's areas 3b and 1, respectively. Activities from area 3b consisted of 20- and 30-ms responses. Activities from area 1 consisted of three components peaking at 26, 36 and 49 ms. ES activated one source within SI whose location and orientation were similar to those of the TS-activated area 1 source. Activities from this source consisted of three components peaking at 88, 98 and 109 ms, later by 60 ms than the corresponding TS responses. ES and TS subsequently activated a similar region in the upper bank of the sylvian fissure, corresponding to the secondary somatosensory cortex (SII). The onset latency of the SII activity following ES (109 ms) was later by 29 ms than that of the first SI response (80 ms). Likewise, the onset latency of SII activity following TS (52 ms) was later by 35 ms than that of area 1 of SI (17 ms). Therefore, our results showed that the processing of noxious and innocuous stimuli is similar with respect to the source locations and activation timings within SI and SII except that there were no detectable activations within area 3b following noxious stimulation.

Adult↗

PubMed2003

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 +/- 2.5 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.

Adult↗