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• Amplitude and synchrony of 40-Hz ASSR was decreased by sound pressure change. • Decrease of amplitude and synchrony depended on magnitude of sound pressure change. • Transient 40-Hz ASSR desynchronization might be an index of change detection. A periodic sound with a fixed inter-stimulus interval elicits an auditory steady-state response (ASSR). An abrupt change in a continuous sound is known to affect the brain's ongoing neural oscillatory activity, but the underlying mechanism has not been fully clarified. We investigated whether and how an abrupt change in sound intensity affects the ASSR. The control stimulus was a train of 1-ms clicks with a sound pressure level (SPL) of 70 dB at 40 Hz for 1000 ms. In addition to the control stimulus, we applied six stimuli with changes consisting of a 500-ms train at 70 dB followed by a 500-ms similar train with louder clicks of 75, 80, or 85 dB or weaker clicks of 55, 60, or 65 dB. We obtained the magnetoencephalographic responses from 15 healthy subjects while presenting the seven stimuli randomly. The two-dipole model obtained for the 40-Hz ASSR in the control condition was applied to all of the stimulus conditions for each subject, and then the time–frequency analysis was conducted. We observed that both the amplitude and the inter-trial phase coherence of the 40-Hz ASSR transiently decreased and returned to the steady state after the change onset, i.e., the desynchronization of 40-Hz ASSR. The degree of desynchronization depended on the magnitude of the change regardless of whether the sound intensity increased or decreased, which might be a novel neurophysiological index of cerebral response driven by a change in the sensory environment. [ABSTRACT FROM AUTHOR]

An ultimate goal of materials science is to deliver materials with desired properties at will. Solving the inverse problem to obtain an appropriate Hamiltonian directly from the desired properties has the potential to reach qualitatively new principles, but most research to date has been limited to quantitative determination of parameters within known models. Here, we develop a general framework that can automatically design a Hamiltonian with desired physical properties by using automatic differentiation. In the application to the quantum anomalous Hall effect, our framework can not only construct the Haldane model automatically but also generate Hamiltonians that exhibit a six-times larger anomalous Hall effect. In addition, the application to the photovoltaic effect gives an optimal Hamiltonian for electrons moving on a noncoplanar spin texture, which can generate ~ 700 Am−2 under solar radiation. This framework would accelerate materials exploration by automatic construction of models and principles. Obtaining a Hamiltonian that produces desired physical properties is important in materials design, that is, however, a highly nontrivial process since the parameter space is usually unknown a priori. Here, the authors present a general theoretical framework based on the inverse problem that uses automatic differentiation to construct a Hamiltonian with the desired physical properties. [ABSTRACT FROM AUTHOR]

The 40-Hz auditory steady-state response (ASSR) is influenced not only by parameters such as attention, stimulus type, and analysis level but also by stimulus duration and inter-stimulus interval (ISI). In this meta-analysis, we examined these parameters in 33 studies that investigated 40-Hz ASSRs in patients with schizophrenia. The average Hedges' g random effect sizes were − 0.47 and − 0.43 for spectral power and phase-locking, respectively. We also found differences in ASSR measures based on stimulus duration and ISI. In particular, ISI was shown to significantly influence differences in the 40-Hz ASSR between healthy controls and patients with schizophrenia. We proposed a novel hypothesis focusing on the role of novelty detection, dependent on stimulus duration and ISI, as a critical factor in determining these differences. Specifically, longer stimulus durations and shorter ISIs under random presentation, or shorter stimulus durations and longer ISIs under repetitive presentation, decrease the 40-Hz ASSR in healthy controls. Patients with schizophrenia show minimal changes in response to stimulus duration and ISI, thus reducing the difference between controls and patients. This hypothesis can consistently explain most of the studies that have failed to show a reduction in 40-Hz ASSR in patients with schizophrenia. Increased novelty-related activity, reflected as an increase in auditory evoked potential components at stimulus onset, such as the N1, could suppress the 40-Hz ASSR, potentially reducing the peak measures of spectral power and phase-locking. To establish the 40-Hz ASSR as a truly valuable biomarker for schizophrenia, further systematic research using paradigms with various stimulus durations and ISIs is needed. • Stimulus duration and inter-stimulus interval influence ASSR. • Novelty detection variations differentiate schizophrenia from control groups. • Novelty-related activity may attenuate the 40-Hz ASSR in healthy individuals. • Challenges remain in using 40-Hz ASSR as a schizophrenia biomarker. [ABSTRACT FROM AUTHOR]

Humans perceive continuous speech signals as discrete sequences. To clarify the temporal segmentation window of speech information processing in the human auditory cortex, the relationship between speech perception and cortical responses was investigated using auditory evoked magnetic fields (AEFs). AEFs were measured while participants heard synthetic Japanese words /atataka/. There were eight types of /atataka/ with different speech rates. The durations of the words ranged from 75 to 600 ms. The results revealed a clear correlation between the AEFs and syllables. Specifically, when the durations of the words were between 375 and 600 ms, the evoked responses exhibited four clear responses from the superior temporal area, M100, that corresponded not only to the onset of speech but also to each group of consonant/vowel syllable units. The number of evoked M100 responses was correlated to the duration of the stimulus as well as the number of perceived syllables. The approximate range of the temporal segmentation window limit of speech perception was considered to be between 75 and 94 ms. This finding may contribute to optimizing the temporal performance of high-speed synthesized speech generation systems. [ABSTRACT FROM AUTHOR]

• CPM was observed objectively using blink reflexes and a cold stimulus to the hand. • Nociceptive- but not non-nociceptive blink reflex was suppressed. • Perceived sensations were suppressed for both noxious and innocuous stimuli. • Effects on the sensation suggested mechanisms higher than the medulla. • Results of blink reflex indicated pain-specific mechanisms at medullary dorsal horn. Although conditioned pain modulation (CPM) is considered to represent descending pain inhibitory mechanisms triggered by noxious stimuli applied to a remote area, there have been no previous studies comparing CPM between pain and tactile systems. In this study, we compared CPM between the two systems objectively using blink reflexes. Intra-epidermal electrical stimulation (IES) and transcutaneous electrical stimulation (TS) were applied to the right skin area over the supraorbital foramen to evoke a nociceptive or a non-nociceptive blink reflex, respectively, in 15 healthy males. In the test session, IES or TS were applied six times and subjects reported the intensity of each stimulus on a numerical rating scale (NRS). Blink reflexes were measured using electromyography (R2). The first and second sessions were control sessions, while in the third session, the left hand was immersed in cold water at 10 °C as a conditioning stimulus. The magnitude of the R2 blink and NRS scores were compared among the sessions by 2-way ANOVA. Both the NRS score and nociceptive R2 were significantly decreased in the third session for IES, with a significant correlation between the two variables; whereas, TS-induced non-nociceptive R2 did not change among the sessions. Although the conditioning stimulus decreased the NRS score for TS, the CPM effect was significantly smaller than that for IES (p = 0.002). The present findings suggest the presence of a pain-specific CPM effect to a heterotopic noxious stimulus. [ABSTRACT FROM AUTHOR]

Despite their essential roles in signal processing in the brain, the functions of interneurons currently remain unclear in humans. We recently developed a method using the prepulse inhibition of sensory evoked cortical responses for functional measurements of interneurons. When a sensory feature is abruptly changed in a continuous sensory stimulus, change-related cortical responses are recorded using MEG. By inserting a weak change stimulus (prepulse) before the test change stimulus, it is possible to observe the inhibition of the test response. By manipulating the prepulse–test interval (PTI), several peaks appear in inhibition, suggesting the existence of temporally distinct mechanisms. We herein attempted to separate these components through the oral administration of diazepam and baclofen. The test stimulus and prepulse were an abrupt increase in sound pressure in a continuous click train of 10 and 5 dB, respectively. The results obtained showed that the inhibition at PTIs of 10 and 20 ms was significantly greater with diazepam than with the placebo administration, suggesting increased GABAA-mediated inhibition. Baclofen decreased inhibition at PTIs of 40 and 50 ms, which may have been due to the activation of GABAB autoreceptors. Therefore, the present study separated at least two inhibitory mechanisms pharmacologically. [ABSTRACT FROM AUTHOR]

Despite their indispensable roles in sensory processing, little is known about inhibitory interneurons in humans. Inhibitory postsynaptic potentials cannot be recorded non-invasively, at least in a pure form, in humans. We herein sought to clarify whether prepulse inhibition (PPI) in the auditory cortex reflected inhibition via interneurons using magnetoencephalography. An abrupt increase in sound pressure by 10 dB in a continuous sound was used to evoke the test response, and PPI was observed by inserting a weak (5 dB increase for 1 ms) prepulse. The time course of the inhibition evaluated by prepulses presented at 10–800 ms before the test stimulus showed at least two temporally distinct inhibitions peaking at approximately 20–60 and 600 ms that presumably reflected IPSPs by fast spiking, parvalbumin-positive cells and somatostatin-positive, Martinotti cells, respectively. In another experiment, we confirmed that the degree of the inhibition depended on the strength of the prepulse, but not on the amplitude of the prepulse-evoked cortical response, indicating that the prepulse-evoked excitatory response and prepulse-evoked inhibition reflected activation in two different pathways. Although many diseases such as schizophrenia may involve deficits in the inhibitory system, we do not have appropriate methods to evaluate them; therefore, the easy and non-invasive method described herein may be clinically useful. [ABSTRACT FROM AUTHOR]

We previously demonstrated that auditory-evoked cortical responses were suppressed by a weak leading stimulus in a manner similar to the prepulse inhibition (PPI) of startle reflexes. The purpose of the present study was to investigate whether a similar phenomenon was present in the somatosensory system, and also whether this suppression reflected an inhibitory process. We recorded somatosensory-evoked magnetic fields following stimulation of the median nerve and evaluated the extent by which they were suppressed by inserting leading stimuli at an intensity of 2.5-, 1.5-, 1.1-, or 0.9-fold the sensory threshold (ST) in healthy participants (Experiment 1). The results obtained demonstrated that activity in the secondary somatosensory cortex in the hemisphere contralateral to the stimulated side (cSII) was significantly suppressed by a weak leading stimulus with the intensity larger than 1.1-fold ST. This result implied that the somatosensory system had an inhibitory process similar to that of PPI. We then presented two successive leading stimuli before the test stimulus, and compared the extent of suppression between the test stimulus-evoked responses and those obtained with the second prepulse alone and with two prepulses (first and second) (Experiment 2). When two prepulses were preceded, cSII responses to the second prepulse were suppressed by the first prepulse, whereas the ability of the second prepulse to suppress the test stimulus remained unchanged. These results suggested the presence of at least two individual pathways; response-generating and inhibitory pathways. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Previous studies showed that the amplitude and latency of the auditory offset cortical response depended on the history of the sound, which implicated the involvement of echoic memory in shaping a response. When a brief sound was repeated, the latency of the offset response depended precisely on the frequency of the repeat, indicating that the brain recognized the timing of the offset by using information on the repeat frequency stored in memory. In the present study, we investigated the temporal resolution of sensory storage by measuring auditory offset responses with magnetoencephalography (MEG). The offset of a train of clicks for 1 s elicited a clear magnetic response at approximately 60 ms (Off-P50m). The latency of Off-P50m depended on the inter-stimulus interval (ISI) of the click train, which was the longest at 40 ms (25 Hz) and became shorter with shorter ISIs (2.5∼20 ms). The correlation coefficient r2 for the peak latency and ISI was as high as 0.99, which suggested that sensory storage for the stimulation frequency accurately determined the Off-P50m latency. Statistical analysis revealed that the latency of all pairs, except for that between 200 and 400 Hz, was significantly different, indicating the very high temporal resolution of sensory storage at approximately 5 ms. [ABSTRACT FROM AUTHOR]

Highlights: [•] The face inversion effect on steady-state visual-evoked magnetic fields was studied. [•] Upright and inverted faces elicited clear SSVEF responses. [•] Face inversion delayed the latency of SSVEFs in the right temporal area. [•] SSVEF amplitudes were not different between upright and inverted faces. [•] Different systems may lie in the delayed and enhanced responses by face inversion. [ABSTRACT FROM AUTHOR]

The choice of a system specific stimulus is difficult when investigating the human nociceptive system, in contrast with the tactile, auditory and visual systems, because it should be noxious but not actually damage the tissue. The discomfort accompanying system specific stimulation must be kept to a minimum for ethical reasons. In this review, recent progress made in the study of human pain perception using intraepidermal electrical stimulation (IES) is described. Also, whether IES is a viable alternative to laser stimulation is discussed. IES selectively activates A&dgr; nociceptors, elicits a sharp pricking sensation with minimal discomfort and evokes cortical responses almost identical to those produced by laser stimulation. As IES does not require expensive equipment, and is easy to control, it would seem useful for pain research as well as clinical tests. [ABSTRACT FROM AUTHOR]

Background: Frontal intermittent rhythmic delta activity (FIRDA) on electroencephalography (EEG) consists of a run of rhythmic delta waves with frontal predominance. Although FIRDA is a relatively common abnormal EEG finding, the underlying mechanisms that produce FIRDA remain unclear. The aim of this study was to investigate the cortical source of FIRDA using dipole source modeling. Methods: We selected EEG epochs, including typical FIRDAs, from EEG recordings obtained using 25 scalp electrodes on 5 subjects. We averaged these epochs by arranging the negative peaks of the delta waves at the Fp electrodes and estimated dipoles for nine averaged waveforms. Results: Averaged waveforms were explained by a single-dipole model in seven FIRDAs and by a two-dipole model in the remaining two FIRDAs with high reliability. Estimated dipoles had a radial orientation with respect to the frontal pole and were located in the medial frontal region. The anterior cingulate cortex was the most common dipole location. Conclusions: This is the first study to approach the fundamental FIRDA mechanism by dipole source modeling and to clarify that FIRDA may be generated from the medial frontal region, particularly from the anterior cingulate cortex. Copyright © 2012 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: 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 100ms). Results: Results show that (i) off-M100 was clearly elicited by the ISI-25 and 50ms conditions but not ISI-75 and 100ms 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 75ms, 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 &y& Elsevier]

Abstract: 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 &y& Elsevier]

Abstract: Among various kinds of visual motion, wide field coherent visual motion should have characteristic physiological significance regarding the relationship between the external world and us. To detect veridical visual motion in the surrounding environment, specific mechanisms are necessary to differentiate it from the wide field coherent motion due to one''s own movement. To disclose whether and how the neural process of wide field coherent motion is different from that of other motions, we measured cortical responses to visual motions in humans using magnetoencephalography (MEG) manipulating both field size and coherence. Results showed that an increase in field size enhanced the response at sensors around the parieto-occipital area, and that the difference in activity between coherent and incoherent motion tended to be larger for the wide field. These findings suggest that wide field coherent and incoherent motion is detected differently at least in part in the parieto-occipital area, and suggest the neural process of wide field coherent motion could be pronouncedly tapped by a combination of field size and coherence. [Copyright &y& Elsevier]

We recorded cortical activity in response to the onset, offset, and frequency change of a pure tone using magnetencephalograms (MEGs) to clarify the physiological significance of N1m relating to the detection of changes. Four interstimulus intervals (ISIs) (0.5, 1.5, 3, and 6 s) were used for each of the three auditory events. Results showed that (i) all three auditory events elicited N1m with a similar topography and similar temporal profile, (ii) the source of N1m was located in the superior temporal gyrus (STG) for all events under all ISI conditions, (iii) the amplitude of the STG activity as a function of the duration of the steady state preceding the change was similar among the three events, and (iv) there was a significant positive correlation in amplitude between on-N1m and off-N1m and between on-N1m and change-N1m. These results suggested that N1m for the three events has a similar physiological significance relating to the detection of changes. [ABSTRACT FROM AUTHOR]

In this study, the cortical dynamics of the visual change detection process were investigated using an oddball paradigm similar to that used in auditory mismatch negativity studies. When subjects watched a silent movie, color stimuli were presented using 280 dual color LEDs arranged along the frame of the video screen. Task-irrelevant red and blue color stimuli were presented randomly at a probability of 10% and 90%, respectively, in one session and vice versa for the other one, and we traced brain responses using magnetoencephalography. Results show that activation in the middle occipital gyrus (MOG) was significantly enhanced for the infrequent stimulus, while early activities in Brodmann's area 17/18 were comparable for the frequent and infrequent stimuli. These results suggest that automatic visual change detection is associated with the MOG activity. [ABSTRACT FROM AUTHOR]

Abstract: Detecting a visual change was suggested to relate closely to the visual sensory memory formed by visual stimuli before the occurrence of the change, because change detection involves identifying a difference between ongoing and preceding sensory conditions. Previous neuroimaging studies showed that an abrupt visual change activates the middle occipital gyrus (MOG). However, it still remains to be elucidated whether the MOG is related to visual change detection based on sensory memory. Here we tried to settle this issue using a new method of stimulation with blue and red LEDs to emphasize a memory-based change detection process. There were two stimuli, a standard trial stimulus and a deviant trial stimulus. The former was a red light lasting 500ms, and the latter was a red light lasting 250ms immediately followed by a blue light lasting 250ms. Effects of the trial–trial interval, 250∼2000ms, were investigated to know how cortical responses to the abrupt change (from red to blue) were affected by preceding conditions. The brain response to the deviant trial stimulus was recorded by magnetoencephalography. Results of a multi-dipole analysis showed that the activity in the MOG, peaking at around 150ms after the change onset, decreased in amplitude as the interval increased, but the earlier activity in BA 17/18 was not affected by the interval. These results suggested that the MOG is an important cortical area relating to the sensory memory-based visual change-detecting system. [Copyright &y& Elsevier]

Background: The rapid detection of sensory change is important to survival. The process should relate closely to memory since it requires that the brain separate a new stimulus from an ongoing background or past event. Given that sensory memory monitors current sensory status and works to pick-up changes in real-time, any change detected by this system should evoke a change-related cortical response. To test this hypothesis, we examined whether the single presentation of a sound is enough to elicit a change-related cortical response, and therefore, shape a memory trace enough to separate a subsequent stimulus. Results: Under a paradigm where two pure sounds 300 ms in duration and 800 or 840 Hz in frequency were presented in a specific order at an even probability, cortical responses to each sound were measured with magnetoencephalograms. Sounds were grouped to five events regardless of their frequency, 1D, 2D, and 3D (a sound preceded by one, two, or three different sounds), and 1S and 2S (a sound preceded by one or two same sounds). Whereas activation in the planum temporale did not differ among events, activation in the superior temporal gyrus (STG) was clearly greater for the different events (1D, 2D, 3D) than the same event (1S and 2S). Conclusions: One presentation of a sound is enough to shape a memory trace for comparison with a subsequent physically different sound and elicits change-related cortical responses in the STG. The STG works as a real-time sensory gate open to a new event. [ABSTRACT FROM AUTHOR]

Background: The detection of any abrupt change in the environment is important to survival. Since memory of preceding sensory conditions is necessary for detecting changes, such a change-detection system relates closely to the memory system. Here we used an auditory change-related N1 subcomponent (change-N1) of event-related brain potentials to investigate cortical mechanisms underlying change detection and echoic memory. Results: Change-N1 was elicited by a simple paradigm with two tones, a standard followed by a deviant, while subjects watched a silent movie. The amplitude of change-N1 elicited by a fixed sound pressure deviance (70 dB vs. 75 dB) was negatively correlated with the logarithm of the interval between the standard sound and deviant sound (1, 10, 100, or 1000 ms), while positively correlated with the logarithm of the duration of the standard sound (25, 100, 500, or 1000 ms). The amplitude of change-N1 elicited by a deviance in sound pressure, sound frequency, and sound location was correlated with the logarithm of the magnitude of physical differences between the standard and deviant sounds. Conclusions: The present findings suggest that temporal representation of echoic memory is non-linear and Weber- Fechner law holds for the automatic cortical response to sound changes within a suprathreshold range. Since the present results show that the behavior of echoic memory can be understood through change-N1, change-N1 would be a useful tool to investigate memory systems. [ABSTRACT FROM AUTHOR]

We recorded cortical activities in response to the onset and offset of a pure tone of long duration (LONG) and a train of brief pulses of a pure tone with an interstimulus interval of 50 ms (ISI–50 ms) or 100 ms (ISI–100 ms) by use of magnetoencephalograms in 11 healthy volunteers to clarify temporal and spatial profiles of the auditory on- and off-cortical response. Results showed that a region around the superior temporal gyrus (STG) of both hemispheres responded to both the onset and offset of the stimulus. The location of the source responsible for the main activity (N1m) was not significantly different between the on- and off-responses for any of the three tones. The peak latency of on-N1m was similar under the three conditions, while the peak latency of off-N1m was precisely determined by the ISI, which suggested that off-N1m is based on short-term memory of the stimulus frequency. In addition, there was a positive correlation of the N1m amplitude of N1m between the on- and off-responses among the subjects. The present results suggested that auditory on-N1m and off-N1m have similar physiological significance involved in responding to abrupt changes. [ABSTRACT FROM AUTHOR]

Abstract: The electrical stimulation of an uncut peripheral nerve requires a countermeasure to avoid the spread of current through a loop pathway formed outside the electrode array. Here the use of tripolar electrodes (TE) is proposed. By binding the two end poles, current spread through the loop pathway can theoretically be eliminated since both end poles are held equipotential. Experimentally, we tested the validity of this approach. In chloralose–urethane anesthetized rats, the left cervical vagus (LCV) was placed on TE which could function as such or as bipolar electrodes (BE) by the use of a selector switch. The spread of current to the adjacent tissues (rectus capitis muscle underlying the LCV, and the right cervical vagus (RCV) incised and translocated beside the target, LCV) was compared between TE and BE. When the stimulus intensity was increased, contraction occurred in the capitis muscle with BE, but not TE. Compound spike potentials of A fiber origin were evoked in the non-target RCV on high-intensity stimulation with BE, but not TE. Constant voltage stimulation of the LCV with TE produced bradycardia of the same magnitude as that with BE. In conclusion, constant voltage stimulation using TE can minimize current spread without changing the stimulus''s effects. [Copyright &y& Elsevier]

Abstract: We recorded cortical activities in response to the onset and offset of a train of electrical pulses applied to the right hand in eleven healthy volunteers by the use of magnetoencephalograms to clarify temporal and spatial profiles of the somatosensory on- and off-cortical responses. Results showed that a region around the upper bank of the sylvian fissure of both hemispheres responded to the onset and offset of the stimulus, while the activity in the primary somatosensory cortex (SI) of the hemisphere contralateral to the stimulation was clear only for the onset response. The SI activity consisted of two components suggesting that two distinct populations of neurons in SI were involved in processing a train of pulses. The location of the source of activity in the contralateral para-sylvian region (cPara) differed significantly between the on- and off-response, while that of the activity in the ipsilateral para-sylvian region (iPara) did not. The differences in location of the cPara activity might be caused by the overlapping of several cortical activities in response to each stimulus and stimulus event (on and off events), while the iPara activity might reflect purely the event-related response. Moreover, some subjects had clear iPara activity without cPara activity especially in the off-response, suggesting the iPara activity to be independent of the cPara activity. We consider that activities in the parasylvian region are involved in the detection of changes at the body''s surface. [Copyright &y& Elsevier]

Background: To segregate luminance-related, face-related and non-specific components involved in spatio-temporal dynamics of cortical activations to a face stimulus, we recorded cortical responses to face appearance (Onset), disappearance (Offset), and change (Change) using magnetoencephalography. Results: Activity in and around the primary visual cortex (V1/V2) showed luminance-dependent behavior. Any of the three events evoked activity in the middle occipital gyrus (MOG) at 150 ms and temporo-parietal junction (TPJ) at 250 ms after the onset of each event. Onset and Change activated the fusiform gyrus (FG), while Offset did not. This FG activation showed a triphasic waveform, consistent with results of intracranial recordings in humans. Conclusion: Analysis employed in this study successfully segregated four different elements involved in the spatio-temporal dynamics of cortical activations in response to a face stimulus. The results show the responses of MOG and TPJ to be associated with non-specific processes, such as the detection of abrupt changes or exogenous attention. Activity in FG corresponds to a face-specific response recorded by intracranial studies, and that in V1/V2 is related to a change in luminance. [ABSTRACT FROM AUTHOR]

Quick detection of changes in the sensory environment is very important for survival, resulting in automatic shifts of attention to the event and the facilitation of subsequent processes to execute appropriate behaviors. The abrupt onset or offset of a sensory stimulus should also activate the neural network detecting changes. To test this hypothesis, we compared cortical on- and off-responses using somatosensory-evoked potentials (SEPs) elicited by a train of electrical pulses delivered to the right hand in eight healthy volunteers. SEPs were recorded from 15 electrodes on the scalp at three different interstimulus intervals (ISIs, 50, 20, and 10 ms) under two sets of conditions (attended and unattended). Both the onset and offset of stimulation evoked two similar components, P100 and N140, in the attended and unattended conditions. The latency of P100 and N140 in response to stimulus onset did not differ among the three ISIs, while the latency of both components in response to stimulus offset was significantly longer for the longer ISI; that is, detection of the cessation of the stimulation was based on short-term memory of the stimulus frequency. The present results supported a cortical network triggered by both the onset and offset of sensory stimulation. In this network, the change is automatically detected using a memory trace by comparing the abrupt event (on or off) with the preceding condition (silent or repetitive stimuli). [ABSTRACT FROM AUTHOR]

Abstract: Evidence suggests that the arterial baroreceptors modulate pain. To examine whether cortical processing of nociception is modulated by natural variations in arterial baroreceptor stimulation during the cardiac cycle, peak-to-peak amplitudes of the N2–P2 pain-related potential and pain ratings were recorded in response to noxious laser stimulation at different times during the cardiac cycle in 10 healthy males. Significant variations in the N2–P2 amplitudes occurred across the cardiac cycle, with smaller amplitudes midcycle, indicating that cortical processing of nociception was attenuated during systole compared to diastole. Pain ratings did not vary across the cardiac cycle. These data support the hypothesis that arterial baroreceptors modulate the processing of nociception during each cardiac cycle. [Copyright &y& Elsevier]

Abstract: 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 83ms), 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 453ms), paired stimuli clearly evoked 1M and 2M. At a long SOA, the peak latency of 2M (around 200ms) was significantly longer than that in the control (S2 alone) condition (around 180ms). 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. [Copyright &y& Elsevier]

Background: Temporal low-voltage irregular δ-waves (TLID) are often found in elderly subjects. The physiological significance of TLID has not been clarified; however, our previous studies suggest that TLID are associated with mild cerebrovascular dysfunction. Objective: The present study aimed to reveal the origin of TLID and their neural mechanisms by dipole source modeling. Methods: From electroencephalography records taken from 21 scalp electrodes, clear and typical TLID of 6 elderly subjects (mean age, 69 ± 6.2 years) were selected. Among these, we selected and averaged 7–12 clear TLID on the left side in each subject, and estimated a single equivalent current dipole for the averaged TLID. Results: The best equivalent current dipoles were estimated to be located in the medial part of the temporal lobe in or near the parahippocampal gyrus in the hemisphere ipsilateral to the TLID, with a high reliability in all subjects. Conclusions: Considering the source localization of TLID, TLID seem to indicate certain dysfunctions of the hippocampus or adjacent regions. This is the first study to report the cerebral origin of TLID and suggest its physiological significance. Copyright © 2008 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Lasers can selectively activate the nociceptors of A-delta fibers. Since nociceptors in the skin are activated via temperature conduction by the laser beam, a latency jittering of cortical responses among trials would affect results obtained with a conventional averaging (C-AVE) technique. We therefore used a new method, latency-adjusted averaging (L-AVE), to investigate cortical responses to noxious laser stimulation in normal subjects. L-AVE was done by averaging trials after adjusting the latency so that the peak latency of an activity in the temporal region of all trials matched on the time axis. Both in C-AVE and in L-AVE, clear activations were found in the contralateral primary somatosensory cortex (SI) and bilateral parasylvian regions, whose activities peaked 163–181 ms after the stimulation. In addition to these three main activities, weak activities peaking at around 109–119 ms could be identified in only L-AVE in similar cortical regions. Since the direction of the source differed between early and main activities, we considered that the early weak activities were cancelled out by the later main activities with an opposite orientation. The results suggested that early cortical processing of noxious information occurs earlier than previous neurophysiological studies have estimated and that the temporal sequence of activations should be reconsidered. [ABSTRACT FROM AUTHOR]

Abstract: To investigate the pathways of noxious information in the spinal cord in humans, we recorded cortical potentials following the stimulation of A-delta fibers using a YAG laser applied to two cutaneous points on the back at the C7 and Th10 level, 4cm to the right of the vertebral spinous process. A multiple source analysis showed that four sources were activated; the primary somatosensory cortex (SI), bilateral parasylvian region (Parasylvian), and cingulate cortex. The activity of the cingulate cortex had two components (N2/P2). The mean peak latencies of the activities obtained by C7 and Th10 stimulation were 166.9 and 186.0ms (SI), 144.3 and 176.8ms (contralateral Parasylvian), 152.7 and 185.5ms (ipsilateral Parasylvian), 186.2 and 215.8ms (N2), and 303.0 and 332.3ms (P2). Estimated spinal conduction velocities (CVs) of the respective activities were 16.8, 9.3, 8.7, 10.1 and 10.7m/s. CV of SI was significantly faster than the others (P <0.05). Therefore, our results suggested that noxious signals were conveyed through at least two distinct pathways of the spinal cord probably reaching distinct groups of thalamic nuclei. Further studies are required to clarify the functional significance of these two pathways. [Copyright &y& Elsevier]

Abstract: 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 150ms 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. [Copyright &y& Elsevier]

Abstract: Nogo-related brain potentials may not be dependent on sensory modalities but reflect common neural activities specific to the inhibitory process. Recent studies reported that nogo potentials were elicited by not only visual and auditory but also somatosensory stimulation. However, the characteristics of this nogo potential evoked by somatosensory stimulation have been unclear because of the small number of reports. In the present study, therefore, to determine the characteristics of this potential, the effects of stimulus site and response hand were investigated. 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. The amplitudes of the nogo-N140 component (N140 evoked by the nogo stimuli), which is very similar to the nogo-N2 components following visual and auditory stimulation, were unrelated to the stimulated digits, the second and fifth digit of the left and right hand. However, differences between go and nogo ERPs were significantly larger in the hemisphere contralateral to the response hand than the ipsilateral hemisphere. This result was inconsistent with visual and auditory go/nogo studies showing a right-hemisphere dominance or bilateral activities in nogo trials. Therefore, nogo-N140 should be considered to reflect the inhibitory process especially in the hemisphere contralateral to the response hand and the sensory modality dependency of nogo potentials. [Copyright &y& Elsevier]

Abstract: Emission and excitation spectra of the 3s2 1S0–3s3p 1P1 transition of Mg atom in pressurized liquid helium-4 and helium-3 have been measured. In the emission spectra we have found that their transition wavelengths, which are significantly red shifted, remain constant or slightly increase with increasing the liquid helium pressure, whereas for other alkali–earth atoms the increase of the liquid pressure always shifts their emission spectra toward shorter wavelength. Our theoretical calculations based on a bubble model have successfully reproduced this unique spectral property, and have suggested the possibility of the formation of a Mg(3s3p 1P1)He n exciplex in a bubble. [Copyright &y& Elsevier]

Abstract: To clarify the latency of the earliest cortical activity in visual processing, electroretinograms (ERGs) and visual evoked magnetic fields (VEFs) following flash stimulation were recorded simultaneously in six human subjects. Flash stimuli were applied to the right eye and ERGs were recorded from a skin electrode placed on the lower lid. ERGs showed two major deflections in all subjects: an eyelid-negativity around 20 ms and a positivity around 60 ms corresponding to an a- and b-waves, respectively. The mean onset and peak latency of the earliest component of VEFs (37M) was 30.2 and 36.9 ms, respectively. There was a linear correlation between the peak latency of the a-wave and the onset latency of the 37M (r = 0.90, P = 0.011). When a single equivalent current dipole analysis was applied to the 37M, four out of six subjects showed highly reliable results. The generator of the 37M was estimated to be located in the striate cortex in all four subjects. Since postreceptoral activities in the retina are expected to start around the peak of the a-wave (20 ms), the early cortical activity, which appears 10 ms later than the a-wave peak, is considered to be the earliest cortical activity following flash stimulation. [Copyright &y& Elsevier]

The go/nogo task is a useful paradigm for recording event-related potentials (ERPs) to investigate the neural mechanisms of response inhibition. In nogo trials, a negative deflection at around 140–300 ms (N2), which has been called the ‘nogo potential’, is elicited at the frontocentral electrodes, compared with ERPs recorded in go trials. In the present study, we investigated the generators of nogo potentials by recording ERPs and by using magnetoencephalography (MEG) simultaneously during somatosensory go/nogo tasks to elucidate the regions involved in generating nogo potentials. ERP data revealed that the amplitude of the nogo-N140 component, which peaked at about 155 ms from frontocentral electrodes, was significantly more negative than that of go-N140. MEG data revealed that a long-latency response peaking at approximately 160 ms, termed nogo-M140 and corresponding to nogo-N140, was recorded in only nogo trials. The equivalent current dipole of nogo-M140 was estimated to lie around the posterior part of the inferior frontal sulci in the prefrontal cortex. These results revealed that both nogo-N140 and nogo-M140 evoked by somatosensory go/nogo tasks were related to the neural activity generated from the prefrontal cortex. Our findings combining MEG and ERPs clarified the spatial and temporal processing related to somato-motor inhibition caused in the posterior part of the inferior frontal sulci in the prefrontal cortex in humans. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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 Aδ 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 Aδ 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 Aδ 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 Aδ 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. [Copyright &y& Elsevier]

Abstract: We used magnetoencephalography (MEG) to study effects of sleep on cortical responses to noxious stimuli and to clarify the mechanisms underlying pain perception. For a noxious stimulus, painful intraepidermal electrical stimulation (ES), which selectively activates A-delta fibers, was applied to the dorsum of the left hand. While awake, subjects were asked to count the number of stimuli silently (Attention) or ignore the stimuli (Control). During sleep, magnetic fields recorded in stage 1 sleep and stage 2 sleep were analyzed. One main component at a latency around 140–160 ms was identified in the awake condition. Multiple source analysis indicated that this main component was generated by activities in the contralateral primary somatosensory cortex (SI), bilateral secondary somatosensory cortex (SII) and insular cortex. The medial temporal area (MT) and cingulate cortex were activated later than the main component. Cortical responses in the contralateral SI, ipsilateral SII and MT, bilateral insula, and cingulate cortex were significantly enhanced in Attention as compared with Control. The main component 1M, as well as later magnetic fields, was markedly attenuated during sleep, suggesting that all these cortical areas are involved in pain cognition. [Copyright &y& Elsevier]

Abstract: When the same visual stimulus is repeatedly presented with a brief interval, the brain''s responses to that stimulus are attenuated relative to those at first presentation (neural adaptation, NA). Although this effect has been widely observed in various regions of human brain, its temporal dynamics as a neuronal population has been mostly unclear. In the present study, we used a magnetoencephalography (MEG) and conducted a macrolevel investigation of the temporal profiles of the NA occurring in the human visual ventral stream. We dissociated three dimensions of the NA: activation strength, peak latency, and temporal duration of neural response. The results revealed that visual responses to the repeated as compared with novel stimulus showed a significant reduction in both activation strength and peak latency but not in the duration of neural processing. These results indicate that (i) the NA involves brain response changes in the temporal domain as well as the response attenuation reported previously, and (ii) this temporal change is mainly observed as a rapid rising of ‘what’ responses rather than a temporal shortening of neural response curves within the visual ventral stream as previously considered. [Copyright &y& Elsevier]

When the same visual stimulus is repeatedly presented with a brief interval, the brain responses to that stimulus are attenuated relative to those at first presentation [neural adaptation (NA)]. Although this effect has been widely observed in various regions of human brain, its temporal dynamics as a neuronal population has been mostly unclear. In the present study, we used a magnetoencephalography (MEG) and conducted a macrolevel investigation of the temporal profiles of the NA occurring in the human visual ventral stream. The combination of MEG with our previous random dot blinking method isolated the neural responses in the higher visual cortex relating to shape perception. We dissociated three dimensions of the NA: activation strength, peak latency, and temporal duration of neural response. The results revealed that visual responses to the repeated compared with novel stimulus showed a significant reduction in both activation strength and peak latency but not in the duration of neural processing. Furthermore, this acceleration of peak latency showed a significant correlation with reaction time of the subjects, whereas no correlation was found between the reaction time and the temporal duration of neural responses. These results indicate that (1) the NA involves the brain response changes in the temporal domain as well as the response attenuation reported previously, and (2) this temporal change is primarily observed as a rapid rising of "what" responses, rather than a temporal shortening of neural response curves within the visual ventral stream as considered previously. [ABSTRACT FROM AUTHOR]

Saposins (SAPs) are small glycoproteins required for activation of sphingolipid hydrolysis by lysosomal enzymes. Four SAPs, SAP-A, -B, -C, and -D, are proteolytically cleaved from a single gene product termed prosaposin. The mature coding sequence of human SAP-A tagged with 6-histidine was expressed in Pichia pastoris and the recombinant protein was purified from the culture supernatant by simple purification steps with an immobilized metal ion affinity column, a Concanavalin A column, and reversed-phase HPLC. Secreted SAP-A contained both glycosylated and nonglycosylated forms. Both forms of SAP-A activated galactocerebroside and 4-methylumbelliferyl β-d-glucoside hydrolysis by galactocerebrosidase and glucocerebrosidase. SAP-A expressed in P. pastoris should be useful for further structural and functional analysis of this protein. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

We investigated the effects of sleep on pain-related somatosensory evoked magnetic fields (SEFs) following painful electrical stimulation to identify the mechanisms generating them in both fast A-beta fibers relating to touch and slow A-delta fibers relating to pain. While the subjects were awake, non-painful and painful electrical stimulations were applied, and while asleep, painful stimulation was applied to the left index finger. During awake, five components (1M–5M) were identified following both non-painful and painful stimulation, but the 4M and 5M at around 70–100 ms and 140–180 ms, respectively, were significantly enhanced following painful stimulation. During sleep, 1M and 2M generated in the primary somatosensory cortex (SI) did not show a significant change, 3M in SI showed a slight but significant amplitude reduction, and 4M and 5M generated in both SI and the secondary somatosensory cortex (SII) were significantly decreased in amplitude or disappeared. The 4M and 5M are complicated components generated in SI and SII ascending through both A-beta fibers and A-delta fibers. They are specifically enhanced by painful stimulation due to an increase of signals ascending through A-delta fibers, and are markedly decreased during sleep, because they much involve cognitive function. [Copyright &y& Elsevier]

We investigated effects of sleep on pain-related somatosensory evoked potentials (SEP) following painful electrical stimulation of the left index finger. The biggest advantage of this method is that signals ascending through both A-beta fibers relating to touch and A-delta fibers relating to pain can be recorded simultaneously. While the subject was awake, non-painful stimulation evoked early- and middle latency components, N20, P30 and N60, at the C4 electrode, and painful stimulation evoked not only early- and middle latency components at the C4 but also later pain-specific components, N130 and P240, at the Cz electrode. During sleep, N20 and P30 did not show a significant change in amplitude, N60 showed a slight but significant amplitude reduction, and N130 and P240 significantly decreased in amplitude or disappeared, as compared with those while awake. Therefore, we speculate on the mechanisms generating each component as follows; (1) N20 and P30 are the primary components generated in SI ascending through A-beta fibers. (2) N60 is the secondary component generated in SI involving cognitive function to some degree. (3) N130-P240 are the pain-specific components ascending through A-delta fibers, and closely related to cognitive function, because they were much affected by consciousness, different from the components ascending through A-beta fibers. [Copyright &y& Elsevier]