Search

The present study investigated the effects of hypocapnia and hypercapnia on human somatosensory processing by utilizing somatosensory evoked magnetic fields (SEFs) with magnetoencephalography (MEG). Thirteen volunteers participated in two experiments separately to measure respiratory and cardiovascular data and SEFs. Both experiments consisted of a combination of normal and rapid respiratory rhythms and two inspiratory gas conditions (air and a hypercapnic gas); normal breathing with air (NB), rapid breathing with air (RB), normal breathing with the hypercapnic gas (NB+Gas), and rapid breathing with gas (RB+Gas). Partial pressures of end-tidal CO 2 (P ETCO2 ) increased during inhaling the hypercapnic gas and decreased during RB, but the RB+Gas condition continued to cause elevated PETCO 2 compared with the baseline. Subsequently, middle cerebral artery blood (MCA) velocity using transcranial Doppler changed as well, while mean MCA velocity increased under the RB+Gas condition. The peak amplitude of the M60 component in SEFs was also significantly larger under with-gas than without-gas conditions, irrespective of the respiratory frequency. These results suggest that there is a close relationship between cerebral blood flow and neural activity of the M60 component in SEFs. This study provides evidence to further understanding on one of the neural mechanisms of hypercapnia., Competing Interests: Declaration of Competing Interest No conflicts of interest, financial or otherwise, are declared by the author(s)., (Copyright © 2022 Japan Neuroscience Society and Elsevier Ltd. All rights reserved.)

Nerve conduction studies (NCS) are an essential aspect of the assessment of patients with peripheral neuropathies. However, conventional NCS do not reflect activation of small afferent fibers, including Aδ and C fibers. A definitive gold standard for laboratory evaluation of these fibers is still needed and therefore, clinical evaluation remains fundamental in patients with small fiber neuropathies (SFN). Several clinical and research techniques have been developed for the assessment of small fiber function, such as (i) microneurography, (ii) laser evoked potentials, (iii) contact heat evoked potentials, (iv) pain-related electrically evoked potentials, (v) quantitative thermal sensory testing, (vi) skin biopsy-intraepidermal nerve fiber density and (vii) corneal confocal microscopy. The first five are physiological techniques, while the last two are morphological. They all have advantages and limitations, but the combined use of an appropriate selection of each of them would lead to gathering invaluable information for the diagnosis of SFN. In this review, we present an update on techniques available for the study of small afferent fibers and their clinical applicability. A summary of the anatomy and important physiological aspects of these pathways, and the clinical manifestations of their dysfunction is also included, in order to have a minimal common background., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)

Magnetoencephalography (MEG) records weak magnetic fields outside the human head and thereby provides millisecond-accurate information about neuronal currents supporting human brain function. MEG and electroencephalography (EEG) are closely related complementary methods and should be interpreted together whenever possible. This manuscript covers the basic physical and physiological principles of MEG and discusses the main aspects of state-of-the-art MEG data analysis. We provide guidelines for best practices of patient preparation, stimulus presentation, MEG data collection and analysis, as well as for MEG interpretation in routine clinical examinations. In 2017, about 200 whole-scalp MEG devices were in operation worldwide, many of them located in clinical environments. Yet, the established clinical indications for MEG examinations remain few, mainly restricted to the diagnostics of epilepsy and to preoperative functional evaluation of neurosurgical patients. We are confident that the extensive ongoing basic MEG research indicates potential for the evaluation of neurological and psychiatric syndromes, developmental disorders, and the integrity of cortical brain networks after stroke. Basic and clinical research is, thus, paving way for new clinical applications to be identified by an increasing number of practitioners of MEG., (Copyright © 2018 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)

The rapid detection of changes in sensory information is an essential process for survival. Individual humans are thought to have their own intrinsic preattentive responsiveness to sensory changes. Here we sought to determine the relationship between auditory change-related responses and personality traits, using event-related potentials. A change-related response peaking at approximately 120 ms (Change-N1) was elicited by an abrupt decrease in sound pressure (10 dB) from the baseline (60 dB) of a continuous sound. Sixty-three healthy volunteers (14 females and 49 males) were recruited and were assessed by the Temperament and Character Inventory (TCI) for personality traits. We investigated the relationship between Change-N1 values (amplitude and latency) and each TCI dimension. The Change-N1 amplitude was positively correlated with harm avoidance scores and negatively correlated with the self-directedness scores, but not with other TCI dimensions. Since these two TCI dimensions are associated with anxiety disorders and depression, it is possible that the change-related response is affected by personality traits, particularly anxiety- or depression-related traits., (Copyright © 2015 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.)

Objective: Itching can be suppressed by scratching. However, scratching may aggravate itch symptoms by damaging the skin. Therefore, identifying an alternative approach to suppress itching is of clinical importance. The aim of the present study was to determine whether a transcranial direct current stimulation (tDCS) was useful for itch relief., Methods: The present study was performed on a double-blind, Sham-controlled, and cross-over experimental design. A histamine-induced itch was evoked on the left dorsal forearms of healthy participants, who were asked to report the subjective sensation of itching every 30s for 23 min. tDCS was applied over the sensorimotor cortex (SMC) according to a bi-hemispheric stimulation protocol during the itch stimuli; one electrode was placed over the right SMC, while the other was placed over the left SMC. The peak and lasting sensations of itching were compared between R-A/L-C (anodal electrode placed over the right and cathodal electrode over the left), L-A/R-C (anodal electrode placed over the left and cathodal electrode over the right), and Sham interventions., Results: The peak and lasting itch sensation were significantly suppressed during the R-A/L-C intervention than during the Sham intervention. On the other hand, the L-A/R-C intervention suppressed the peak itch sensation, but the effects did not last for more than a few minutes., Conclusions: These results suggest that a bi-hemispheric tDCS intervention, especially when the anodal electrode was placed over the SMC of the contralateral side, was a potentially useful method for relieving lasting itch sensations., Significance: The present study demonstrated that a tDCS intervention may be an alternative approach for suppressing unpleasant itch sensations in healthy participants. Since tDCS has some advantages, namely, its easy application and safety in a clinical setting, it may become a useful method for the treatment of itching., (Copyright © 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Objective: The purpose of the present study was to investigate the effect of mastication on Go/No-go decisional processing using event-related potentials (ERPs)., Method: Thirteen normal subjects underwent seven sessions of a somatosensory Go/No-go paradigm for approximately 4min; Pre, and Post 1, 2, 3, 4, 5, and 6. The Control condition included the same seven sessions. The RT and standard deviation were recorded, and the peak amplitude and latency of the N140 and P300 components were analyzed., Results: The RT was significantly shorter in Mastication than in Control at Post 1-3 and 4-6. The peak latency of N140 was earlier in Mastication than in Control at Post 4-6. The latency of N140 was shortened by repeated sessions in Mastication, but not by those in Control. The peak latency of P300 was significantly shorter in Mastication than in Control at Post 4-6. The peak latency of P300 was significantly longer in Control with repeated sessions, but not in Mastication., Conclusions: These results suggest that mastication may influence response execution processing in Go trials, as well as response inhibition processing in No-go trials., Significance: Mastication accelerated Go/No-go decisional processing in the human brain., (Copyright © 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Itch is a complex sensory and emotional experience. Functional brain imaging studies have been performed to identify brain regions associated with this complex experience, and these studies reported that several brain regions are activated by itch stimuli. The possible roles of these regions in itch perception and difference in cerebral mechanism between healthy subjects and chronic itch patients are discussed in this review article. Additionally, the central itch modulation system and cerebral mechanisms of contagious itch, pleasurable sensation evoked by scratching have also been investigated in previous brain imaging studies. We also discuss how these studies advance our understanding of these mechanisms., (Copyright © 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Objective: To investigate whether intraepidermal electrical stimulation (IES) can evaluate nociceptive Aδ- and C-fiber dysfunctions of an experimental model of small-fiber neuropathy (SFN) with transdermal lidocaine., Methods: Lidocaine tape or placebo was applied to the dorsum of the feet in 14 healthy subjects. Reaction time (RT), sensory threshold, and evoked potentials (EPs) were measured using IES before, and 30 and 60 min after lidocaine/placebo application., Results: All subjects felt pricking sensations following Aδ-fiber stimulation, and light painful sensations such as pricking, tingling, or burning following C-fiber stimulation using IES. RT was divided bimodally between Aδ- and C-fiber stimulations. At 30 min, lidocaine increased the sensory threshold and decreased the amplitude of EPs in both fiber stimulations. At 60 min, lidocaine's effects were greater for C fibers than for Aδ fibers. The sensory threshold and amplitude of EPs were unchanged among placebo sessions., Conclusions: IES demonstrated differential effects of transdermal lidocaine on nociceptive Aδ and C fibers, and elucidated the pathophysiology of the experimental model of SFN., Significance: IES has advantages in terms of cost, convenience, and invasiveness. It may have potential for a clinical tool to elucidate the pathophysiology of patients with SFN, including the differences between Aδ and C fibers., (Copyright © 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Objective: In contrast to tactile inputs, the organization and processing of nociceptive inputs in the primary somatosensory cortex (S1) remain largely unexplored. Few studies have examined the arrangement of nociceptive inputs in S1. The aim of this study was to investigate the representation of nociceptive inputs in the human cortex, including the somatosensory and posterior parietal cortices, from widely separated cutaneous sites., Methods: We examined the somatotopic organization of the nociceptive system in S1, opercular and posterior parietal cortices by measuring the magnetoencephalographic responses (somatosensory-evoked magnetic fields) of four healthy controls in response to intraepidermal electrical stimulation applied to the face, neck, back, elbow, wrist, hand, finger, knee, and foot, which selectively activated the Aδ fibers., Results: Magnetoencephalography demonstrated clear somatotopy in the S1 responses to noxious stimuli, with the foot representation in the extreme posteromedial position of S1 and the facial area in the extreme anterolateral position. There was little evidence of any clear somatotopic organization in the secondary somatosensory and posterior parietal cortices., Conclusion: These findings suggest that the nociceptive system uses the large body surface map in S1., Significance: This is the first MEG study to demonstrate the cortical representation of nociceptive inputs in the human S1. We showed that widely separated cutaneous sites clearly supported Penfield's homunculus., (Copyright © 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Event-related potentials were measured in twenty-four children aged 6-15 years, at one-year intervals for two years, to investigate developmental changes in each subject's neural response to a point-light walker (PLW) and a scrambled PLW (sPLW) stimulus. One positive peak (P1) and two negative peaks (N1 and N2) were observed in both occipitotemporal regions at approximately 130, 200, and 300-400ms. The amplitude and latency of the P1 component measured by the occipital electrode decreased during development over the first one-year period. Negative amplitudes of both N1 and N2, induced by the PLW stimulus, were significantly larger than those induced by the sPLW stimulus. Moreover, for the P1-N1 amplitude, the values for the eight-year-old children were significantly larger than those for the twelve-year-old children. N1 and N2 latency at certain electrodes decreased with age, but no consistent changes were observed. These results suggest that enhanced electrophysiological responses to PLW can be observed in all age groups, and that the early components were changed even over the course of a single year at the age of twelve., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Objective: In order to evaluate whether face perception is intact or not in Williams syndrome (WS), the face inversion effects (FIE) in the event-related potential (ERP) or magnetoencephalography (MEG) were investigated in three teenaged patients with WS., Methods: Responses to the inverted faces and upright faces were compared using MEG for one 13year old girl with WS (subject A) and ERP for boys with WS at 16 and 14years of age (subjects B and C, respectively)., Results: Although age-matched control children showed FIE in both MEG and ERP studies, two subjects (A and B) with WS showed no FIE at all. The neurophysiological data of ERP in subject B was significantly different from those of the age-matched controls. On the other hand, a boy with WS (subject C) showed typical FIE in the same manner as the age-matched controls., Conclusions: The difference between those with or without FIE was not explained merely by the chronological age, a simple delay in mental age or in the ability to discriminate among upright faces. The absence of FIE may be related to the severity of a deficit in the dorsal pathway function that is characteristic to the syndrome., (Copyright © 2012 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.)

Objective: We investigated the characteristics of cortical rhythmic activity in No-go processing during somatosensory Go/No-go paradigms, by using magnetoencephalography (MEG)., Methods: Twelve normal subjects performed a warning stimulus (S1) - imperative stimulus (S2) task with Go/No-go paradigms. The recordings were conducted in three conditions. In Condition 1, the Go stimulus was delivered to the second digit, and the No-go stimulus to the fifth digit. The participants responded by pushing a button with their right thumb for the Go stimulus. In Condition 2, the Go and No-go stimuli were reversed. Condition 3 was the resting control., Results: A rebound in amplitude was recorded in the No-go trials for theta, alpha, and beta activity, peaking at 600-900 ms. A suppression of amplitude was recorded in Go and No-go trials for alpha activity, peaking at 300-600 ms, and in Go and No-go trials for beta activity, peaking at 200-300 ms., Conclusion: The cortical rhythmic activity clearly has several dissociated components relating to different motor functions, including response inhibition, execution, and decision-making., Significance: The present study revealed the characteristics of cortical rhythmic activity in No-go processing., (Copyright © 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Quickly detecting changes in the surrounding environment is one of the most important functions of sensory processing. Comparison of a new event with preceding sensory conditions is necessary for the change-detection process. A sudden change in a continuous sound elicits auditory evoked potentials that peak approximately 100 ms after the onset of the change (Change-N1). In the present study, we recorded Change-N1 under an oddball paradigm in 19 healthy subjects using an abruptly moving sound (SM-stimulus) as a deviant stimulus and investigated effects of the probability of the SM-stimulus to reveal whether Change-N1 is a memory-based response. We compared the amplitude and latency of Change-N1 elicited by the SM-stimulus among three probability conditions (33, 50 and 100%). As the probability of the SM-stimulus decreased, the amplitude of Change-N1 increased and its latency decreased. The present results indicate that the preceding sensory history affects Change-N1 elicited by the SM-stimulus., (Copyright © 2012 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.)

Objective: We sought to clarify the presence of a temporal window of integration (TWI) in the somatosensory modality by manipulating the inter-stimulus interval (ISI)., Methods: We recorded cortical activity following the last of a train of electric pulses (stimulus offset) applied to the left hand in nine healthy volunteers using magnetoencephalography (MEG). Somatosensory evoked magnetic fields (SEFs) were elicited by the offset of a train of pulses 3s in total duration with four ISIs (25, 50, 75, and 100 ms)., Results: Results show that (i) off-M100 was clearly elicited by the ISI-25 and 50 ms conditions but not ISI-75 and 100 ms conditions, and (ii) the generator for off-M100 was mainly located in the contralateral primary and secondary somatosensory cortex (SI and SII)., Conclusion: The upper limit of the TWI in the somatosensory modality is between 50 and 75 ms, and the contralateral SI and SII play an important role in integrating temporal information., Significance: The present study clarifies the presence of the TWI in the somatosensory modality., (Copyright © 2011 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

To test the hypothesis that the N1 component of auditory evoked potentials (AEPs) is one form of the change-related response elicited by an abrupt change in sound pressure from a silent background, two AEP experiments were conducted. Change-N1 was evoked by a test stimulus at 70dB following a 3-s conditioning stimulus of 0-69dB. On-N1 was evoked by the test sound alone at various sound pressures. As the physical difference between stimuli increased, the amplitude of Change-N1 increased, and the latency shortened. The amplitude and latency of On-N1 showed a similar pattern to the Change-N1 response. These results support the idea that On-N1 is a change-related component elicited by a sound pressure change., (Copyright © 2011 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.)

Skin pain and muscle pain are categorically distinct from each other. While skin pain is a sharp, spatially localized sensation, muscle pain is a dull, poorly localized and more unpleasant one. We hypothesized that there are specific brain regions preferentially activated by muscle pain compared to skin pain. To test this hypothesis, brain responses were recorded from 13 normal male subjects in response to repeated painful electrical stimulation of the muscle and skin of the left leg, using 3-T magnetic resonance imaging scanner. The common brain regions that responded to painful stimulations of both skin and muscle were the thalamus, anterior cingulate cortex, bilateral insula, contralateral primary and secondary somatosensory cortices, and ipsilateral cerebellum. Brain regions specifically activated by muscle stimulation were the midbrain, bilateral amygdala, caudate, orbitofrontal cortex, hippocampus, parahippocampus and superior temporal pole, most of which are related to emotion. Regions except the midbrain showed contralateral preference. These results suggest that dull sensation, which is characteristic of muscular pain, is related with processing in these brain regions., (Copyright © 2011 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.)

Objective: To determine if there is an optimum spatial extent for the detection of moving objects in humans., Methods: We investigated human brain responses to motion at various speeds (2.9-23.5 deg/s) and stimulus sizes (2.2 × 2.9 deg to 44.8 × 57.4 deg) using magnetoencephalography. The results were compared with those for the flickers with the same stimulus sizes and temporal frequencies., Results: For every size, response latency was inversely related to speed. Further, the latency was lowest at a stimulus size of 16.8 × 22.4 deg for every speed. Although response latency was inversely related to the temporal frequency of the flicker stimulation for all stimulus sizes, it was not affected by stimulus size as much as motion stimulus., Conclusions: For visual motion detection, the most efficient stimulus size is around 16.8 × 22.4 deg., Significance: The results suggest that spatial summation mechanism is important for the detection of visual motion but a loss of reference frame information affects the detection of larger motion stimuli, supporting the view that illusory self-motion (vection) is caused by poor reference frame information for motion detection., (Copyright © 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Objective: The development of the perception of changes in facial emotion was investigated using event-related potentials (ERPs) in children and adults., Methods: Four different conditions were presented: (1) N-H: a neutral face that suddenly changed to a happy face. (2) H-N: reverse of N-H. (3) N-A: a neutral face that suddenly changed to an angry face. (4) A-N: reverse of N-A., Results: In the bilateral posterior temporal areas, a negative component was evoked by all conditions in younger children (7-10 years old), older children (11-14 years old), and adults (23-33 years old) within 150-300 ms. Peak latency was significantly shorter and amplitude was significantly smaller in adults than younger and older children. Moreover, maximum amplitude was significantly larger for N-H and N-A than H-N and A-N in younger children and for N-H than the other three conditions in adults., Conclusion: The areas of the brain involved in perceiving changes in facial emotion have not matured by 14 years of age., Significance: Our study is the first to clarify a difference between children and adults in the perception of facial emotional change., (Copyright © 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Previously, we used near-infrared spectroscopy (NIRS) to measure infant's brain activity during face processing by detecting changes in hemodynamic responses, oxy-Hb, deoxy-Hb, and total-Hb concentrations [1,2]. We found that the right temporal cortex of the brain was activated when infants looked at upright frontal faces rather than inverted faces, and at the frontal view as well as the profile view on 8-month-olds. In the present study, we investigated 7- and 8-month-olds' brain activity related to the perception of mother's and stranger's faces by NIRS. The finding was that oxy-Hb and total-Hb concentrations in the right temporal cortex increased against the baseline during presentation of the mother's face. For strangers' faces, the total-Hb concentration in the right temporal cortex was greater than the baseline. By contrast, oxy- and total-Hb concentrations in the left temporal cortex increased only in the presentation of mother's face. The great activity in the right temporal region for faces irrespective of familiarity was consistent with a predominance of the right temporal cortex found previously in infants [1,2] as well as functional magnetic resonance imaging (fMRI) studies in adults [3,4]. In contrast to the activity in the right temporal cortex, the greater hemodynamic response in the left temporal cortex was observed only in the mother's face condition. These findings suggest that the processing of the mother's face enhances activity in bilateral temporal cortex. This is the first study to clarify the location of brain activity in infants related to the perception of their mother's face., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

The somatic sensation of the tongue is necessary for daily life, but it is difficult to know the underlying neural mechanisms. In particular, because of the vomiting reflex and several morphological problems, no neuroimaging studies have examined somatosensory processing by stimulating the posterior part of the tongue, except for two magnetoencephalographic studies (Sakamoto et al., 2008a,b). This is the first study to clarify the human cortical processing for sensory perception by the posterior part of the tongue with a newly developed device and functional magnetic resonance imaging (fMRI). Stimulation of the left and right postero-lateral parts of the tongue induced significant activity in the primary somatosensory cortex (SI) and Brodmann area 40 in the right hemisphere and the anterior cingulate cortex (ACC). In contrast, antero-lateral stimulation produced activity only in the right SI. The activated region in SI was significantly larger following stimulation of the posterior than anterior part. These results indicate that a clear difference exists in somatosensory processing between stimulation of the antero-lateral and postero-lateral parts of the tongue, and a right hemisphere is dominant for the stimulation of both antero-lateral and postero-lateral areas. The activity in BA 40 and ACC may imply that the posterior of the tongue belongs to the visceral system.

We studied the human brain response to visual stimulation in which a square area was randomly presented in upper and lower visual fields (VFs). Seven normal volunteers carried out a contrast-based visual search task. Magnetic responses were detected in the bilateral parietal regions at 200-250 ms after stimulus onset. We compared the response latencies and strengths of the essential single sensor and root mean square (RMS) of the regions. The former evaluates the strength of neural activity with relatively high spatial resolution, while the latter evaluates the global neural activity. The single sensor and RMS latencies for the lower left VF were significantly longer than that for the upper left (paired t-test, P<0.05). The strengths did not differ between the upper and lower left VFs. There was no significant difference in latency or strength between the upper right and lower right VFs. These findings suggest that only left VF has different response properties in the upper versus lower VF, and that both local and global extrastriate activities are responsible for this anisotropy.

To clarify the effect of mastication on motor preparation processing using electroencephalography (EEG), we investigated the effect of mastication on contingent negative variation (CNV) and reaction time (RT) in Experiment 1, and movement-related cortical potentials (MRCPs) in Experiment 2. The twelve subjects performed four CNV or MRCP sessions, and in the Mastication condition chewed a gum base during the resting period between sessions, Pre (before chewing) and Post 1, 2, and 3 (after chewing). In the Control condition, the subjects performed the same sessions without chewing gum during the intervals between sessions on another day. In Experiment 1, the mean amplitudes of the early- and late-CNV were significantly larger in Mastication than Control at Post 2 and Post 3. RT also differed significantly between Mastication and Control at Post 3. By contrast, in Experiment 2, there were no significant differences between Mastication and Control for the mean amplitudes of MRCPs including Bereitschaftspotential (BP) and negative slope (NS') in any session. These results suggest that mastication influences cognitive processing reflected by CNV with stimulus-triggered movement, rather than motor-related processing reflected by MRCPs relating to self-initiated movement, and provide evidence concerning the mechanisms for the effect of mastication on the human brain.

Objective: The purpose of the present study was to clarify the effect of mastication on cognitive processing using reaction time (RT) and event-related potentials (ERPs)., Methods: The two experiments consisted of two conditions, Mastication (chewing gum) and Control (relaxing without chewing gum) in Experiment 1, and Jaw Movement (opening and closing the jaw) and Finger Tapping (tapping the right index finger) in Experiment 2. The subjects performed four sessions of an auditory oddball paradigm. RT and ERPs were recorded in these four sessions, Pre (before chewing), and Post 1, Post 2 and Post 3 (after chewing)., Results: In Mastication for RT and the peak latencies of P300 and N100, the values were significantly longer in Pre than in Post 2 or Post 3. By contrast, in Control, Jaw Movement, and Finger Tapping, they were almost identical among sessions or significantly shorter in Pre than in Post 2 or Post 3., Conclusions: Mastication influences cognitive processing time as reflected by RT and the latency of ERP waveforms., Significance: This is the first study investigating the effect of mastication on the central nervous system using event-related potentials.

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.

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.

We examined effects of the interval between first (S1) and second (S2) visual stimuli, stimulus-onset asynchrony (SOA), on the cortical processing of S2 using magnetoencephalography (MEG). S1 (a circle) and S2 (a cross) were presented at the same location. When the SOA was short (33, 50, and 83 ms), the major deflection of the fields evoked in response to S2 (2M) was difficult to distinguish from that evoked by S1 (1M). However, when the SOA was long (350 and 453 ms), paired stimuli clearly evoked 1M and 2M. At a long SOA, the peak latency of 2M (around 200 ms) was significantly longer than that in the control (S2 alone) condition (around 180 ms). However, in contrast, the reaction time to S2 in all SOA conditions was significantly shortened as compared with that in the control condition, suggesting dissociation between processing in the visual cortex and motor processing.

The human visual system is considered to have at least two different mechanisms for perceiving motions: one for luminance-based (first-order) motions and another for non-luminance-based (second-order) motions. In this study, we examined the perception of first- and second-order motions using four different types of stimulus cues (luminance, contrast, texture, and flicker) while using whole head magnetoencephalography (MEG) to measure human brain responses to those apparent motions. MEG responses to all stimuli were recorded from the occipito-temporal area (possibly human MT/V5+), and response properties (peak latency and amplitude) varied with stimulus cues. Further, we observed various effects of luminance-addition to the non-luminance cues on the response properties that could not be explained by the magnetic field distribution and/or the visibility of the stationary object. The results indicate that differences in response properties elicited by various stimulus cues represent differences in the neural processes underlying apparent motions with various cues. We suggest that the distinct "preprocessing" of each stimulus cue occurs before the common process for apparent motion, and the response property changes associated with different cues are related to differences in preprocessing that may occur in a distributed cortical network that include the striate and extrastriate visual cortex.

Objective: To establish an objective two-point discrimination test using magnetoencephalography (MEG)., Methods: First, we determined the discrimination threshold (DT) of the two-points. In the first experiment, we applied 0.9DT as standard stimuli, and 0.8DT, 1.1DT and 2DT as deviant stimuli in Conditions 1, 2 and 3, respectively. In the second experiment, we used 2DT and 0.9DT as the standard and deviant stimuli, respectively, in Condition 1. We applied two-stimuli that subjects felt as definitely one point or two-points in Condition 2 and 3, respectively., Results: In the first experiment, the components peaking around 30-70 and 150-250ms following deviant stimuli were significantly larger than those following standard stimuli. Considering the peak latency, these components seem consistent with the magnetic mismatch field (MMF). In the second experiment, the MMF was recorded only in Condition 1. Therefore, it is considered that the MMF was recorded only when subjects automatically discriminate one point from two-points stimuli., Conclusions: This novel method can be used in neurophysiological two-point discrimination tests without the need to rely on the examiners' skills and subjects' reactions., Significance: We confirmed that our new method could be used for the objective examination of two-point spatial discrimination.

Objective: To investigate the centrifugal effect on somatosensory evoked potentials (SEPs), we recorded the pre-movement modulation of SEPs following stimulation of the tibial nerve caused by a self-initiated dorsiflexion., Methods: SEPs following stimulation of the right tibial nerve at the popliteal fossa were recorded during self-initiated dorsiflexion of the right ankle every 5-7s. Based on the onset of Bereitschaftspotential and negative slope, the preparatory period before dorsiflexion was divided into four sub-periods (pre-BP, BP1a, BP1b and BP2 sub-period), and SEPs in each sub-period were averaged. SEPs were also recorded in a stationary condition., Results: P30, N40, P50 and N70 were identified at Cz in all subjects. The amplitude of P30 was significantly smaller in the BP2 sub-period than in the pre-BP sub-period. The N40 amplitude was significantly attenuated in the BP2 sub-period compared with the stationary condition, the pre-BP sub-period, the BP1a sub-period and the BP1b sub-period., Conclusions: These results suggested that the motor-related areas involved in generating negative slope modulated the tibial nerve SEPs preceding a self-initiated contraction of the agonist muscle., Significance: The centrifugal gating effect on SEPs extends to the somatosensory information from the antagonistic body part.

Objective: We investigated the effect of the inhibitory process with increasing muscle force on event-related potentials (ERPs) and motor evoked potentials (MEPs)., Methods: The subjects performed a S1-S2 paradigm with go/nogo tasks. S1 was an auditory tone burst, and S2 was an electrical stimulation applied to the second (go stimuli) or fifth digit (nogo stimuli) of the left hand. The recordings were conducted at 3 force levels; 10, 30 and 50% maximal voluntary contraction (MVC). After the presentation of S2, the subjects were instructed to adjust their force level to match the target line with a force trajectory line in only the go trials., Results: Nogo-N140 was significantly more negative in amplitude than go-N140 in all conditions, and became larger with increasing muscle force. The MEP, which was recorded at 150 ms after S2, became significantly smaller with increasing muscle force in nogo trials, whereas it became larger in go trials., Conclusions: Our results indicated that stronger inhibitory cerebral activity was needed for a nogo stimulus, in the case where a stronger response was needed for a go stimulus., Significance: The present study showed a significant relationship between cortical inhibitory process and muscle force.

Objective: To determine the existence of a pre-attentively evoked somatosensory mismatch negativity component and to investigate the use of that component in objective clinical diagnostics., Methods: First we determined the temporal discrimination threshold (DT) of paired stimuli in each subject, and applied two sequential electrical stimuli to the hand with paired stimulus times of (1) DT-10 ms, (2) DT-30 ms and (3) DT+50 ms. Then, we recorded ERPs using an oddball paradigm, frequent (standard) and rare (deviant). We used two stimuli, DT-30 ms and DT-10 ms, in the first experiment, and DT-30 ms and DT+50 ms, in the second experiment., Results: In each experiment, two specific components, a negative component peaking at approximately 60ms (N60) and a large positive component peaking around 100-200 ms (P150), were identified, mainly following the deviant stimulus, which were considered somatosensory mismatch components. N60 was more remarkably identified in the second experiment and P150 in the first., Conclusions: N60 might be generated during tasks which subjects can clearly discriminate, but P150, which seems to correspond to auditory mismatch negativity, might be generated in tasks which require fine discrimination., Significance: We confirmed that our new method could be used for the objective examination of temporal discrimination.

Objective: To investigate the somatotopic organization of the facial skin area in the secondary somatosensory cortex (SII) in humans., Methods: Somatosensory evoked magnetic fields following air-puff stimulation of 5 body sites, the foot, the lip and 3 points of the facial skin (forehead, cheek and mandibular angle point), were recorded. We focused on activities in SII following stimulation of these 5 sites and compared dipole locations among them., Results: There was a clear somatotopic organization in SII with lip in the most lateral area, foot in the most medial area and face in an intermediate area close to the lip area. However, there was no significant difference of dipole localization in SII among the 3 areas of facial skin, similar to the overlapped somatotopic organization of facial skin areas in the primary somatosensory cortex in our previous study., Conclusions: The facial skin areas are considered to occupy a small area in SII with insufficient spatial separation to differentiate each area of facial skin even using magnetoencephalography which has a high spatial resolution., Significance: This is the first systematic study of the activated regions in SII following stimulation of the facial skin.

Objective: We reviewed the recent progress in electrophysiological studies using electroencephalography (EEG), magnetoencephalography (MEG) and repetitive transcranial magnetic stimulation (rTMS) on human pain perception., Methods: For recording activities following A delta fiber stimulation relating to first pain, several kinds of lasers such as CO2, Tm:YAG and argon lasers are now widely used. The activity is frequently termed laser evoked potential (LEP), and we reviewed previous basic and clinical reports on LEP. We also introduced our new method, epidermal stimulation (ES), which is useful for recording brain activities by the signals ascending through A delta fibers. For recording activities following C fiber stimulation relating to second pain, several methods have been used but weak CO2 laser stimuli applied to tiny areas of the skin were recently used., Results: EEG and MEG findings following C fiber stimulation were similar to those following A delta fiber stimulation except for a longer latency. Finally, we reviewed the effect of rTMS on acute pain perception. rTMS alleviated acute pain induced by intracutaneous injection of capsaicin, which activated C fibers, but it enhanced acute pain induced by laser stimulation, which activated A delta fibers., Conclusions: One promising approach in the near future is to analyze the change of a frequency band. This method will probably be used for evaluation of continuous tonic pain such as cancer pain, which evoked response studies cannot evaluate.

To investigate the representation of facial skin areas in the primary somatosensory cortex (SI), we recorded magnetic fields evoked by air pressure-induced tactile stimulation applied to six points on the face, lower lip and thumb. The thumb area in the SI was located more medial and superior to the lip area, which was consistent with Penfield's homunculus. However, the representations of all skin-covered areas including forehead, cheek, nose and chin in the SI were located between the thumb and lower lip area. There was no significant difference in location among the six facial points. Our results imply that lips occupy a large area of the face representation in the SI, whereas only a small area located between the thumb and lip areas is devoted to skin-covered surfaces. This is the first study showing that the facial skin areas in the human SI are located between the thumb and lower lip areas and close together.

Objective: To elucidate the temporal features of the cognitive process in two-point discrimination (TPD)., Methods: We measured somatosensory event-related potentials (ERPs) in 9 subjects during the TPD task, in which we provided a pair of electrical pulses simultaneously, altering the distance between the electrodes. We analyzed the TPD-related ERPs and investigated the relationship between the potentials and the subjects' judgments., Results: During the TPD task, a negative potential approximately 140 ms after the stimulation (N140) was enhanced as compared to a stimulus counting task. Two late positive components, LPC-1 and LPC-2, whose peak latencies were 300 and 500 ms, respectively, were identified only in the TPD task. The LPC-1 was recorded dominantly in the fronto-central area, while the LPC-2 was detected dominantly in the centro-parietal area. The amplitude of the LPC-2 was significantly modulated by the degree of consistency in the subjects' judgment. On the other hand, these ERP components did not show significant difference between the alternate judgments, i.e. 'one-point' or 'two-point' judgment., Conclusions: Our results suggest that the N140 is related to the attention toward the stimulation. The LPC-1 and LPC-2 are likely to correspond to the processes represented by P3a and P3b, based on their temporal and spatial behavior.

Objective: We studied the temporal and spatial characteristics of neural responses elicited by viewing mouth movements using magnetoencephalography., Methods: We focused on differences in responses to mouth opening and closing movements by apparent motion, using an averting eyes condition as a control., Results: A large clear MEG component, 1 M (mean peak latency of approximately 160 ms), was elicited by both mouth movements. We modeled the neural sources using a brain electric source analysis (BESA) method and placed the sources around: (1) the occipitotemporal border at human MT/V5, (2) the primary visual cortex (V1), and (3) fusiform gyrus. The calculated activity of Source (1) was large whereas the activity of the others was small or negligible. Source (1), as calculated separately for mouth closing and opening movements and eye movement, showed no significant different amplitude and locations. We did not find any activity in the superior temporal sulcus (STS)., Conclusions: Our results indicate that human MT/V5 is active in the perception of both mouth and eye motions. Viewing mouth and eye movements elicits no significant differences in MT/V5 activity, indicating that the perception of movement of facial parts is probably processed in the same manner., Significance: Characteristic activities in the human MT/V5 elicited by viewing mouth movement were clarified by MEG.

Objective: Using magnetoencephalography (MEG), we evaluated the cerebral regions relating to second pain perception ascending through C-fibers and investigated the effect of distraction on each region., Methods: Thirteen normal subjects participated in this study. CO2 laser pulses were delivered to the dorsum of the left hand to selectively activate C-fibers. The MEG responses were analyzed using a multi-dipole model., Results: (1) primary somatosensory cortex (SI), and (2) secondary somatosensory cortex (SII)--insula were the main generators for the primary component, 1M, whose mean peak latency was 744 ms. In addition to (1) and (2), (3) cingulate cortex and (4) medial temporal area (MT) were also activated for the subsequent component, 2M, whose mean peak latency was 947 ms. During a mental calculation task (Distraction), all 6 sources were significantly reduced in amplitude, but the SII-insula (P < 0.01) and cingulate cortex (P < 0.001) were more sensitive than the SI (P < 0.05) and MT (P < 0.05)., Conclusions: We confirmed that SI in the contralateral hemisphere and SII-insula, cingulate cortex and MT in bilateral hemispheres play a major role in second pain perception, and all sites were much affected by a change of attention, indicating that these regions are related to the cognitive aspect of second pain perception., Significance: The SI, SII, cingulate and MT were activated during the C-fiber-related MEG response, and responses in these regions were significantly diminished during mental distraction.

Objective: We investigated the effects of a go/nogo task on event-related potentials (ERPs) evoked by somatosensory stimuli., Methods: ERPs 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., Results: N140 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., Conclusions: In 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., Significance: The 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.

Humans perceive motion when numerous small dots pattern is followed by one of the same pattern but with all the dots shifted a little in one direction. When the amount of shift exceeds a level humans no more perceive motion even though physical visual information does not change. Using this stimulus, we addressed to elucidate the temporal structure of the neural activity related to this apparent motion perception. The magnetic responses to the random-dot patterns with various amounts of shift were measured while the subjects were performing a direction discrimination task. A significant magnetic response amplitude change occurred with three distinct peaks when the response inducing apparent motion was compared with those inducing no motion without change in the response latencies. The major difference occurred at about 110, 140, 210 ms after the stimulus onset. The response origin was always within the occipitotemporal area. The results indicate that the neural activity for the perception of apparent motion can be measured by MEG that occur at least 110 ms after the stimulus onset possibly in the human MT+. Three distinct peaks in the response difference may represent the sequential multiple neural process proposed theoretically though further study is necessary to prove.