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The aim of the present study was to investigate the effects of mastication on somatosensory processing using somatosensory-evoked potentials (SEPs). Fourteen healthy subjects received a median nerve stimulation at the right wrist under two conditions: Mastication and Control. SEPs were recorded in five sessions for approximately seven minutes: Pre, Post 1, 2, 3, and 4. Subjects were asked to chew gum for five minutes after one session in Mastication. Control included the same five sessions. The amplitudes and latencies of P14, N20, P25, N35, P45, and N60 components at C3', frontal N30 component at Fz, and P100 and N140 components at Pz were analyzed. The amplitude of P45-N60 was significantly smaller at Post 1, 2, 3, and 4 than at Pre in Control, but not in Mastication. The latency of P25 was significantly longer at Post 2, 3, and 4 than at Pre in Control, but not in Mastication. The latency of P100 was significantly longer at Post 2 than at Pre in Control, but not in Mastication. These results suggest the significant effects of mastication on the neural activity of human somatosensory processing., (Copyright © 2016 Elsevier Ireland Ltd and Japan Neuroscience Society. All rights reserved.)

We investigated the effects of task repetition on the N140 and P300 components of event-related potentials (ERPs) in somatosensory Go/No-go paradigms. A Go or No-go stimulus was presented to the second or fifth digit of the left hand, respectively, at the same probability, and subjects had to respond by pushing a button with their right thumb as quickly as possible only after the presentation of a Go stimulus. The condition comprised seven sessions of recordings, and subjects were allowed to relax for five minutes after one session. The behavioral data for the reaction time (RT), standard deviation of RT, and error rates showed the absence of an effect by task repetition. In ERP waveforms, the amplitudes of N140 and P300 decreased with task repetition, and the latency of P300 was delayed by task repetition. There was no significant effect of task repetition on the peak latency of N140. Changes in amplitude and latency values in N140 and P300 during Go/No-go paradigms reflected changes in the neural activation of response execution and inhibition processing with task repetition., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

We investigated the relationship between reaction time (RT) and response variability and somatosensory Go/No-go potentials. Event-related potentials following electrical stimulation of the second (Go stimulus) or fifth (No-go stimulus) digit of the left hand were recorded from 16 subjects, and Go and No-go stimuli were presented at an even probability. The subjects were instructed to respond to the Go stimuli by pushing a button with their right thumb. We analyzed the correlation between RT and the N140 and P300 components, and between the standard deviation (SD) of RT and the N140 and P300. Neither the amplitude nor latency of the No-go-N140 (N140 evoked by No-go stimuli) or the Go-N140 (N140 evoked by Go stimuli) related significantly with RT and the SD of RT. There was a significant negative correlation between RT and the amplitude of the No-go-P300 (P300 evoked by No-go stimuli) at Fz and C3, indicating that subjects with a shorter RT had a No-go-P300 of larger amplitude. The latency of the Go-P300 (P300 evoked by Go stimuli) at Pz and C3 showed a significant correlation with RT. The SD of RT was significantly correlated with the amplitudes of the No-go-P300 at C3 and Go-P300 at Pz and C4, and the latency of the No-go-P300 at Cz and Go-P300 at Fz, Cz, Pz, C3, and C4. Our results suggest that response speed and variability for the Go stimulus in Go/No-go paradigms affect No-go-related neural activity for the No-go stimulus.

We investigated the relationship between short-latency and long-latency somatosensory-evoked potentials (SEPs) relating to voluntary movement. In general, the amplitudes of short-latency components in SEPs are attenuated during movement, whereas those of long-latency are enhanced, and this phenomenon is termed 'gating effects'. This study aimed to examine the relationship of changes in amplitude between short-latency and long-latency SEPs. SEPs were recorded from 11 participants at Fz, Cz, Pz, and C4' by stimulating the left median nerve. Two tasks were conducted; Control and Movement. In Control, the participant was asked to relax with no specific task. In Movement, the participant was encouraged to continue a rapid drumming motion of all fingers of the left hand at a self-paced rate. The amplitudes of short-latency SEPs, the P25 at C4' and N30 at Fz, were significantly smaller in the Movement than Control condition. By contrast, the amplitudes of long-latency SEPs, the N140 at Fz, Cz, and Pz were significantly larger in Movement than Control condition. Moreover, a significant positive correlation was observed in the rate of amplitude change between the frontal N30 and vertex N140, indicating that for the participants with a frontal N30 of smaller amplitude during Movement, the amplitude of the vertex N140 was smaller. We inferred that the neural activities in movement-related cortices affected the sources for the frontal N30 and vertex N140 in the same neuronal network simultaneously.

This study investigated the characteristics of event-related potentials using somatosensory go/no-go paradigms. We manipulated the interstimulus interval and analyzed its effect on the peak amplitude and latency of the N140 and P300 components. The amplitude of N140 increased as the interstimulus interval increased, and was significantly larger in no-go than in go trials at the 1-s and 2-s interstimulus intervals, but not the 4-s and 6-s interstimulus intervals. The amplitude of P300 also increased with the interstimulus interval, and was significantly larger in no-go than in go trials at all interstimulus intervals. The reaction time in go trials was longer with increasing interstimulus interval. This study suggests that brain activities associated with go/no-go decisional processes are influenced by the interstimulus interval.

The present study investigated one of the characteristics of No-go-related brain activity during somatosensory Go/No-go paradigms, by manipulating the stimulus site and response hand. Somatosensory event-related potentials (ERPs) were recorded in ten right-handed subjects. Electrical stimulation was delivered to the second and fifth digit of one hand, and the subjects had to respond to a Go stimulus by pushing a button with the thumb contralateral to the stimulated side as quickly as possible. We focused on the peak amplitude and latency of Som-Go-P300 (P300 evoked by somatosensory Go stimuli) and Som-No-go-P300 (P300 evoked by somatosensory No-go stimuli) components. The amplitude of Som-No-go-P300, which is very similar to No-go-P300 components following visual and auditory stimulation, was significantly larger than that of Som-Go-P300 at fronto-central electrodes, indicating 'anteriorization' of the No-go-P300. The amplitude of Som-No-go-P300 was significantly larger in right than left hemispheres during right hand response conditions, but this difference was not found under left hand conditions. In addition, the difference in amplitude between Som-Go- and Som-No-go-P300, which is frequently described as 'the Go/No-go effect' on P300, was significant in the left hemisphere under right hand response conditions, whereas a significant effect was found in both the left and the right hemispheres under left hand response conditions. Our findings suggested that the anteriorization of No-go-P300 was independent of stimulus modalities such as visual, auditory, and somatosensory, and the amplitude of No-go-P300 and Go/No-go effects on P300 was affected by the response hand., (Copyright 2010 Elsevier Ireland Ltd. All rights reserved.)

In the present study, we investigate the top-down centrifugal modulation of neural responses to a task-relevant noxious stimulation triggering voluntary movement by recording magnetoencephalography (MEG) and electroencephalography (EEG) simultaneously. An auditory warning signal was followed 2-3 s later by a noxious YAG laser stimulation as an imperative signal delivered to the left hand dorsum. Ten normal subjects performed three different conditions, Control, Movement, and Count. In Control, the subjects were asked to relax and rest quietly with no task. In Movement, the subjects extended the left index finger after imperative stimuli. In Count, the subjects counted the number of imperative stimuli silently. The amplitude of the N2 component recorded by EEG, which peaked about 220 ms after noxious stimulation, was significantly attenuated in Movement, but not in Count, compared to Control. The root-mean-square (RMS) from both hemispheres, and areal mean signal (AMS) amplitudes and the equivalent current dipole (ECD) strengths from SI/PPC and bilateral SII recorded at around 170 ms by MEG were not significantly different among the three conditions. In contrast, ECD strengths and AMS amplitudes from the anterior cingulate cortex (ACC), which showed a similar peak to the N2 component, were smaller in Movement than Control and Count. We therefore suspect that neural activities related to generator mechanisms of N2, especially including ACC, are inhibited by movement-related neural activities during the preparatory period. The present findings indicate a characteristic of pain-motor integration in a movement preparatory period.

Objective: To clarify the somatotopic representation of the tongue secondary somatosensory cortex (SII) in humans., Methods: Somatosensory evoked magnetic fields (SEFs) were recorded from nine subjects after stimulating four body sites, left antero (LA) and postero (LP) lateral margins of the tongue, left median nerve at the wrist (Hand), and left tibial nerve at the ankle (Foot)., Results: Clear neural activities were recorded from the bilateral SII in both hemispheres after the four sites were stimulated. The tongue SII for LA and LP was located close to the hand SII and significantly more anterior than the Foot SII. There was no significant difference in the location of dipoles between the LA and LP areas of the tongue SII. The mean peak latencies of the tongue SII for LA and LP were significantly shorter in the hemisphere contralateral to the stimulation than the ipsilateral hemisphere., Conclusions: The tongue areas are considered to occupy a small region in SII with insufficient spatial separation to differentiate anterior from posterior areas even using magnetoencephalography which has a higher spatial resolution than electroencephalography (EEG)., Significance: This is the first systematical study to clarify the activated regions in SII following stimulation of the tongue.

Primary somatosensory cortex (SI) and posterior parietal cortex (PPC) are activated by noxious stimulation. In neurophysiological studies using magnetoencephalography (MEG), however, it has been difficult to separate the activity in SI from that in PPC following stimulation of the upper limb, since the hand area of SI is very close to PPC. Therefore, we investigated human pain processing using MEG following the application of a thulium-YAG laser to the left thigh to separate the activation of SI and PPC, and to clarify the time course of the activities involved. The results indicated that cortical activities were recorded around SI, contralateral secondary somatosensory cortex (cSII), ipsilateral secondary somatosensory cortex (iSII), and PPC between 150-185 ms. The precise location of PPC was indicated to be the inferior parietal lobule (IPL), corresponding to Brodmann's area 40. The mean peak latencies of SI, cSII, iSII and IPL were 152, 170, 181, and 183 ms, respectively. This is the first study to clarify the time course of the activities of SI, SII, and PPC in human pain processing using MEG.

Objective: To clarify the characteristics relating to the temporal dynamics of the tongue primary somatosensory cortex (SI)., Methods: We fabricated individual intraoral devices and recorded somatosensory-evoked magnetic fields (SEFs) from 10 normal subjects. The tongue was stimulated with a concentrated bipolar electrode in four areas: the right and left antero-lateral margins, and the right and left postero-lateral margins., Results: The primary component was recorded about 19 ms post-stimulation. Six components, termed 1M, 2M, 3M, 4M, 5M, and 6M, respectively, were found within 130 ms of the stimulation. These activities were detected in hemispheres both contralateral and ipsilateral to the stimulation, and were estimated to be located around the tongue SI. In addition, the latency of the contralateral hemisphere was significantly shorter than that of the ipsilateral hemisphere for all components, independent of the area stimulated., Conclusions: Tactile stimulation of the tongue-elicited activity in the tongue SI in both hemispheres., Significance: This is the first study to investigate the brain responses evoked by stimulating different areas of the tongue, using magnetoencephalography.