Brain-wide network analysis of resting-state neuromagnetic data.

The present study performed a brain-wide network analysis of resting-state magnetoencephalograms recorded from 53 healthy participants to visualize elaborate brain maps of phase- and amplitude-derived graph-theory metrics at different frequencies. To achieve this, we conducted a vertex-wise computation of threshold-independent graph metrics by combining proportional thresholding and a conjunction analysis and applied them to a correlation analysis of age and brain networks. Source power showed a frequency-dependent cortical distribution. Threshold-independent graph metrics derived from phase- and amplitude-based connectivity showed similar or different distributions depending on frequency. Vertex-wise age-brain correlation maps revealed that source power at the beta band and the amplitude-based degree at the alpha band changed with age in local regions. The present results indicate that a brain-wide analysis of neuromagnetic data has the potential to reveal neurophysiological network features in the human brain in a resting state.

Effects of hypocapnia and hypercapnia on human somatosensory processing.

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 CO2 (PETCO2) increased during inhaling the hypercapnic gas and decreased during RB, but the RB+Gas condition continued to cause elevated PETCO2 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.

The ERP and psychophysical changes related to facial emotion perception by expertise in Japanese hospitality, "OMOTENASHI".

We investigated the emotion perception process based on hospitality expertise. Forty subjects were divided into the OMOTENASHI group working at inns considered to represent the spirit of hospitality, OMOTENASHI in Japan, and CONTROL group without experience in the hospitality industry. We presented neutral, happy, and angry faces to investigate P100 and N170 by these faces, and psychophysical changes by the favor rating test to evaluate emotional perception. In the favor rating test, the score was significantly smaller (less favorable) in OMOTENASHI than in CONTROL. Regarding event-related potential components, the maximum amplitude of P100 was significantly larger for a neutral face at the right occipital electrode in OMOTENASHI than in CONTROL, and it was significantly larger for an angry face at both occipital electrodes in OMOTENASHI than in CONTROL. However, the peak latency and maximum amplitude of N170 were not significantly different between OMOTENASHI and CONTROL at both temporal electrodes for each emotion condition. Differences on the favor rating test and P100 in OMOTENASHI suggested that workers at inns may more quickly notice and be more sensitive to the facial emotion of guests due to hospitality training, and/or that hospitality expertise may increase attention to emotion by top-down and/or bottom-up processing.

Human Face Perception Using Electroencephalography and Magnetoencephalography.

The face has a large amount of information that is useful for humans in social communication. Recently, non-invasive methods have been used to investigate human brain activity related to perception and cognition processes. Electroencephalography (EEG) and magnetoencephalography (MEG) have excellent temporal resolution and reasonably good spatial resolution. Therefore, they are useful to investigate time sequences of human brain activity related to the face perception process. In this review, we introduce our previous EEG and MEG studies of human face perception that demonstrated the following characteristics of face perception processing: (1) Event-related components in the temporal area related to the activity in the inferior temporal (IT) area, corresponding to the fusiform face area (FFA), are evoked approximately 180 msec after the presentation of a face. The activity in the IT area plays an important role in the detection processing of a face, and the contours of a face affect the activity in the IT areas. (2) Event-related components in the temporal area related to the superior temporal sulcus (STS) activity are larger when eyes are averted than when directly looking into the eyes. (3) The direction of features of a face affects the face perception processing in the right hemisphere. On the other hand, the matching of the direction between the contours and features of a face affects the processing in the left hemisphere. (4) Random dots blinking (RDB), which uses temporal changes in patterns of many small dots to present stimuli without a change in luminance during the presentation of a face, is a useful visual stimulus method to investigate the brain activity related to face perception processing in the IT area using EEG and MEG.

Review of techniques useful for the assessment of sensory small fiber neuropathies: Report from an IFCN expert group.

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.

Effects of passive heat stress and recovery on human cognitive function: An ERP study.

Using event-related potentials (ERPs), we investigated the effects of passive heat stress and recovery on the human cognitive function with Flanker tasks, involving congruent and incongruent stimuli. We hypothesized that modulation of the peak amplitude and latency of the P300 component in ERP waveforms would differ with task difficulty during passive heat stress and recovery. Subjects performed the Flanker tasks before (Pre), at the end of whole body heating (Heat: internal temperature increase of ~1.2°C from the pre-heat baseline), and after the internal temperature had returned to the pre-heat baseline (Recovery). The internal temperature was regulated by a tube-lined suit by perfusing 50°C water for heat stress and 25°C water for recovery immediately after the heat stress. Regardless of task difficulty, the reaction time (RT) was shortened during Heat rather than Pre and Recovery, and standard deviations of RT (i.e., response variability) were significantly smaller during Heat than Pre. However, the peak amplitudes of the P300 component in ERPs, which involved selective attention, expectancy, and memory updating, were significantly smaller during Heat than during Pre, suggesting the impairment of neural activity in cognitive function. Notably, the peak amplitudes of the P300 component were higher during Recovery than during Heat, indicating that the impaired neural activity had recovered after sufficient whole-body cooling. An indicator of the stimulus classification/evaluation time (peak latency of P300) and the RT were shortened during Heat stress, but such shortening was not noted after whole-body cooling. These results suggest that hyperthermia affects the human cognitive function, reflected by the peak amplitude and latency of the P300 component in ERPs during the Flanker tasks, but sufficient treatment such as whole-body cooling performed in this study can recover those functions.

Conditioned Pain Modulation: Comparison of the Effects on Nociceptive and Non-nociceptive Blink Reflex.

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.

Dexterous manual movement facilitates information processing in the primary somatosensory cortex: A magnetoencephalographic study.

The interaction between the somatosensory and motor systems is important for control of movement in humans. Cortical activity related to somatosensory response and sensory perception is modulated by the influence of movement executing mechanisms. This phenomenon has been observed as inhibition in the short-latency components of somatosensory evoked potentials and magnetic fields (SEPs/SEFs). Although finger is the most dexterous among all the body parts, the sensorimotor integration underlying this dexterity has not yet been elucidated. The purpose of this study was to examine the sensorimotor integration mechanisms in the primary somatosensory cortex (SI) during simple and complicated finger movement. The participant performed tasks that involved picking up a wooden block (PM task) and picking up and turning the wooden block 180° (PTM task) using the right-hand fingers. During these tasks, the SEFs following right median nerve stimulation were recorded using magnetoencephalography. The amplitude of the M20 and M30 components showed a significant reduction during both manual tasks compared to the stationary task, whereas the M38 component showed a significant enhancement in amplitude. Furthermore, the SEFs recorded during continuous rotation of the block (rotation task) revealed a characteristic pattern of SI activity that was first suppressed and then facilitated. Since this facilitation is noticeable during complicated movement of the fingers, this phenomenon is thought to underlie a neural mechanism related to finger dexterity.

The Amygdala Network for Processing Itch in Human Brains.

Itch is an unpleasant and aversive somatosensory experience. These negative emotions significantly affect mental health in patients with chronic itch; it is therefore important to understand the brain mechanism of negative emotions due to itch. The amygdala is a key hub of networks regulating negative emotions due to itch. However, the exact network involved in this process is unknown. This study used functional magnetic resonance imaging to investigate the amygdala network processing itch in 25 healthy subjects. Brain activity was measured during electrical itch stimuli using functional magnetic resonance imaging. During itch stimuli the amygdala exhibited increased functional connectivity with key brain regions of the serotonergic system responsible for negative emotions (the medial habenula and the median raphe nucleus) and with the memory system, which is responsible for consolidating emotional experiences (the parahippocampus and perirhinal cortex). The serotonergic and memory systems may become therapeutic targets to prevent or reduce diminished mental health commonly seen in chronic itch patients.

Temporal codes of visual working memory in the human cerebral cortex: Brain rhythms associated with high memory capacity.

Visual working memory (vWM) is an important ability required for various cognitive tasks although its neural underpinnings remain unclear. While many studies have focused on theta (4-7 Hz) and gamma (> 30 Hz) rhythms as a substrate of vWM, here we show that temporal signals embedded in alpha (8-12 Hz) and beta (13-30 Hz) bands can be a good predictor of vWM capacity. Neural activity of healthy human participants was recorded with magnetoencephalography when they performed a classical vWM task (change detection). We analyzed changes in inter-peak intervals (IPIs) of oscillatory signals along with an increase in WM load (a number of to-be-memorized items, 1-6). Results showed a load-dependent reduction of IPIs in the parietal and frontal regions, indicating that alpha/beta rhythms became faster when multiple items were stored in vWM. Furthermore, this reduction in IPIs was positively correlated with individual vWM capacity, especially in the frontal cortex. Those results indicate that vWM is represented as a change in oscillation frequency in the human cerebral cortex.

Infants' recognition of their mothers' faces in facial drawings.

This study examined the development of ability to recognize familiar face in drawings in infants aged 6-8 months. In Experiment 1, we investigated infants' recognition of their mothers' faces by testing their visual preference for their mother's face over a stranger's face under three conditions: photographs, cartoons produced by online software that simplifies and enhances the contours of facial features of line drawings, and veridical line drawings. We found that 7- and 8-month-old infants showed a significant preference for their mother's face in photographs and cartoons, but not in veridical line drawings. In contrast, 6-month-old infants preferred their mother's face only in photographs. In Experiment 2, we investigated a visual preference for an upright face over an inverted face for cartoons and veridical line drawings in 6- to 8-month-old infants, finding that infants aged older than 6 months showed the inversion effect in face preference in both cartoons and veridical line drawings. Our results imply that the ability to utilize the enhanced information of a face to recognize familiar faces may develop aged around 7 months of age.

Hemodynamic response to familiar faces in children with ADHD.

BACKGROUND: School-age children with attention deficit hyperactivity disorder (ADHD) have difficulties in interpersonal relationships, in addition to impaired facial expression perception and recognition. For successful social interactions, the ability to discriminate between familiar and unfamiliar faces is critical. However, there are no published reports on the recognition of familiar and unfamiliar faces by children with ADHD. METHODS: We evaluated the neural correlates of familiar and unfamiliar facial recognition in children with ADHD compared to typically developing (TD) children. We used functional near-infrared spectroscopy (fNIRS) to measure hemodynamic responses on the bilateral temporal regions while participants looked at photographs of familiar and unfamiliar faces. Nine boys with ADHD and 14 age-matched TD boys participated in the study. fNIRS data were Z-scored prior to analysis. RESULTS: During familiar face processing, TD children only showed significant activity in the late phase, while ADHD children showed significant activity in both the early and late phases. Additionally, the boys with ADHD did not show right hemispheric lateralization to familiar faces. CONCLUSIONS: This study is the first to assess brain activity during familiar face processing in boys with ADHD using fNIRS. These findings of atypical patterns of brain activity in boys with ADHD may be related to social cognitive impairments from ADHD.

Effects of whole body skin cooling on human cognitive processing: a study using SEPs and ERPs.

The present study investigated the effect of whole body skin cooling on somatosensory ascending processing by utilizing somatosensory-evoked potentials (SEPs) and motor execution, as well as inhibitory processing by event-related potentials (ERPs). Fourteen healthy participants wearing a water-perfused suit performed two sessions (sessions 1 and 2) consisting of SEPs and ERPs with somatosensory Go/No-go paradigms under two conditions (cold stress and control) on different days. In session 2, under the cold stress condition, whole body skin cooling was achieved by circulating 20°C water through the suit for 40 min, whereas 34°C water was perfused in the other sessions. The mean skin temperature decreased from 35.0 ± 0.5°C (session 1) to 30.4 ± 0.9°C (session 2) during whole body skin cooling, but the internal temperature was maintained. Whole body skin cooling delayed the peak latencies of N20, P25, and P45 components at C4' of SEPs (all: P < 0.05). Moreover, the peak latencies of P14, N18, and P22 components at Fz of SEPs and the Go-P300 component of ERPs were delayed (all: P < 0.05). In contrast, the peak amplitudes of all individual components of SEPs as well as N140 and P300 of ERPs remained unchanged. These results suggest that passive whole body skin cooling delays neural activities on somatosensory processing and higher cognitive function.

The Functional Network Processing Acute Electrical Itch Stimuli in Humans.

The posterior insula (pIns) is a major brain region that receives itch-related signals from the periphery and transfers these signals to broad areas in the brain. Previous brain imaging studies have successfully identified brain regions that respond to itch stimuli. However, it is still unknown which brain regions receive and process itch-related signals from the pIns. Addressing this question is important in identifying key functional networks that process itch. Thus, the present study investigated brain regions with significantly increased functional connectivity with the pIns during itch stimuli with 25 healthy subjects by using functional MRI. Electrical itch stimuli was applied to the left wrist. Similar to previous brain imaging studies, many cortical and subcortical areas were activated by itch stimuli. However, not all of these regions showed significant increments of functional connectivity with the pIns during itch stimuli. While the subjects perceived the itch sensation, functional connectivity was significantly increased between the right pIns and the supplementary motor area (SMA), pre-SMA, anterior midcingulate cortex (aMCC), anterior insula (aIns), secondary somatosensory cortex (SII), and basal ganglia (BG), suggesting that this is a key network in processing itch. In particular, intensity of functional connectivity between the pIns and BG was negatively correlated with itch rating. The functional pIns-BG pathway may play an important role in regulation of subjective itch sensation. This study first identified a key brain network to process itch.

Remote effects on corticospinal excitability during motor execution and motor imagery.

We investigated the remote effect on corticospinal excitability of resting left and right hand muscles during motor execution and motor imagery when performing left or right foot plantar flexion. Fifteen right-handed subjects performed two conditions with three tasks: Condition (Motor Execution (ME) vs. Motor Imagery (MI)): Task (Control, Ipsilateral, and Contralateral). From the left and right first dorsal interosseous, motor evoked potentials (MEPs) elicited by a single-pulse transcranial magnetic stimulation (TMS) to the left or right primary motor cortices (M1) were recorded under all six trials. MEP amplitudes were significantly larger under the ME than MI condition, irrespective of hands and tasks. MEP amplitudes were also the largest during the Contralateral tasks, irrespective of the condition and hands. The correlation analysis showed that MEP amplitudes were significantly correlated between ME and MI conditions with both left and right hands. Our results indicate that the magnitude of the remote effect on corticospinal excitability of hand muscles differs between motor execution and motor imagery, and between ipsi- and contralateral limbs, when performing foot plantar flexion.

Desynchronizing to be faster? Perceptual- and attentional-modulation of brain rhythms at the sub-millisecond scale.

Neural oscillatory signals has been associated with many high-level functions (e.g. attention and working memory), because they reflect correlated behaviors of neural population that would facilitate the information transfer in the brain. On the other hand, a decreased power of oscillation (event-related desynchronization, ERD) has been associated with an irregular state in which many neurons behave in an uncorrelated manner. In contrast to this view, here we show that the human ERD is linked to the increased regularity of oscillatory signals. Using magnetoencephalography, we found that presenting a visual stimulus not only induced a decrease in power of alpha (8-12 Hz) to beta (13-30 Hz) rhythms in the contralateral visual cortex but also reduced the mean and variance of their inter-peak intervals (IPIs). This indicates that the suppressed alpha/beta rhythms became faster (reduced mean) and more regular (reduced variance) during visual stimulation. The same changes in IPIs, especially those of beta rhythm, were observed when subjects allocated their attention to a contralateral visual field. Those results revealed a new role of the event-related decrease in alpha/beta power and further suggested that our brain regulates and accelerates a clock for neural computations by actively suppressing the oscillation amplitude in task-relevant regions.

Effects of repetitive exercise and thermal stress on human cognitive processing.

Cognitive performances may improve after acute moderate exercise, but not after prolonged and/or heavy exercise. The present study aimed to investigate the effects of environmental temperature during exercise on human cognitive processing. Fifteen healthy males performed four bouts of a 15-min cycling exercise with a 10-min rest between each bout, and event-related potentials (ERPs) were recorded in five sessions during somatosensory Go/No-go paradigms (i.e., Pre, post-first exercise bout, post-second exercise bout, post-third exercise bout, and post-fourth exercise bout) in an environmental chamber with temperature controlled at 20°C (Temperate) and 35°C (Hot). Increases in external canal temperature and heart rate were greater under the 35°C condition than under the 20°C condition. Regardless of thermal conditions, reaction times (RT) and error rates were not affected by the repetition of moderate exercise, whereas the peak amplitude of the N140 component, which is mainly related to somatosensory processing, was significantly reduced with the repetition of the exercise. However the peak amplitude of P300, which is linked to cognitive processes of context updating, context closure, and event-categorization, was significantly smaller in post-third and post-fourth exercise bouts under the 35°C condition than under the 20°C condition, and this decrease was more prominent in No-go trials under the 35°C condition. These results suggest that executive function, which is based on RTs and error rates, is not affected by prolonged exercise and different thermal conditions, whereas the exercise in a hot environment impairs human cognitive processing, particularly response inhibition.

Neural correlates of time distortion in a preaction period.

An intention to move distorts the perception of time. For example, a visual stimulus presented during the preparation of manual movements is perceived longer than actual. Although neural mechanisms underlying this action-induced time distortion have been unclear, here we propose a new model in which the distortion is caused by a sensory-motor interaction mediated by alpha rhythm. It is generally known that viewing a stimulus induces a reduction in amplitude of occipital 10-Hz wave ("alpha-blocking"). Preparing manual movements are also known to reduce alpha power in the motor cortex ("mu-suppression"). When human participants prepared movements while viewing a stimulus, we found that those two types of classical alpha suppression interacted in the third (time-processing) region in the brain, inducing a prominent decrease in alpha power in the supplementary motor cortex (SMA). Interestingly, this alpha suppression in the SMA occurred in an asymmetric manner (such that troughs of alpha rhythm was more strongly suppressed than peaks), which can produce a gradual increase (slow shift of baseline) in neural activity. Since the neural processing in the SMA encodes a subjective time length for a sensory event, the increased activity in this region (by the asymmetric alpha suppression) would cause an overestimation of elapsed time, resulting in the action-induced time distortion. Those results showed a unique role of alpha wave enabling communications across distant (visual, motor, and time-processing) regions in the brain and further suggested a new type of sensory-motor interaction based on neural desynchronization (rather than synchronization).

Effects of stimulus intensity and auditory white noise on human somatosensory cognitive processing: a study using event-related potentials.

Exposure to auditory white noise has been shown to facilitate cognitive function. This phenomenon is often called stochastic resonance, and a moderate amount of auditory noise has been suggested to benefit individuals in hypodopaminergic states. Previous studies using psychophysic methods reported that stochastic resonance was sensitive to stimulus intensity; however, the relationship between neural activities elicited by different stimulus intensities and auditory white noise has not yet been clarified Thus, the present study aimed to investigate the effects of stimulus intensity (Experiment 1) and auditory white noise (Experiment 2) on behavioral data (reaction time (RT), the standard deviation of RT, and error rates), and the N140 and P300 components of event-related potentials (ERPs) in somatosensory Go/No-go paradigms. The subjects had to respond to the somatosensory stimuli by pressing a button with their right thumb only after presentation of the Go stimulus. In Experiment 1 with four different stimulus intensity levels, the peak latencies of N140 and P300 became shorter, and the peak amplitudes of N140 and P300 were enhanced with increases in stimulus intensity. In Experiment 2 with weak and mild intensities under auditory white noise and control conditions, the amplitudes of Go-P300 and No-go-P300 were enhanced by white noise, irrespective of weak and mild intensities, during Go/No-go paradigms. Auditory white noise did not significantly affect the amplitude of N140 or the latencies of N140 and P300. These results suggest the presence of a characteristic cross-modal stochastic resonance in neural substrates utilizing somatosensory ERPs.