Koya Yamashiro

Time Course of Activity in Itch-Related Brain Regions: A Combined MEG–fMRI Study

Functional neuroimaging studies have identified itch-related brain regions. However, no study has investigated the temporal aspect of itch-related brain processing. Here this issue was investigated using electrically evoked itch in ten healthy adults. Itch stimuli were applied to the left wrist and brain activity was measured using magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). In the MEG experiment, the magnetic responses evoked by the itch stimuli were observed in the contralateral and ipsilateral frontotemporal regions. The dipoles associated with the magnetic responses were mainly located in the contralateral (nine subjects) and ipsilateral (eight subjects) secondary somatosensory cortex (SII)/insula, which were also activated by the itch stimuli in the fMRI experiment. We also observed an itch-related magnetic response in the posterior part of the centroparietal region in six subjects. MEG and fMRI data showed that the magnetic response in this region was mainly associated with itch-related activation of the precuneus. The latency was significantly longer in the ipsilateral than that in the contralateral SII/insula, suggesting the difference to be associated with transmission in the callosal fibers. The timing of activation of the precuneus was between those of the contralateral and ipsilateral SII/insula. Other sources were located in the premotor, primary motor, and anterior cingulate cortices (one subject each). This study is the first to demonstrate part of the time course of itch-related brain processing. Combining methods with high temporal and spatial resolution (e.g., MEG and fMRI) would be useful to investigate the temporal aspect of the brain mechanism of itch.

Cortical dynamics of the visual change detection process.

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 Brodmanns 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.

Change‐related responses in the human auditory cortex: An MEG study

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.

Automatic auditory off‐response in humans: an MEG study

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.

Somatosensory off-response in humans: An MEG study

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 bodys surface.

Non-linear laws of echoic memory and auditory change detection in humans

BackgroundThe 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.ResultsChange-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.ConclusionsThe 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.

Cortical dynamics of visual change detection based on sensory memory

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 500 ms, and the latter was a red light lasting 250 ms immediately followed by a blue light lasting 250 ms. Effects of the trial-trial interval, 250 approximately 2000 ms, 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 150 ms 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.

Effects of prior sustained tactile stimulation on the somatosensory response to the sudden change of intensity in humans: an magnetoencephalography study

The rapid detection of sensory changes is important to survival. The change-detection system should relate closely to memory since it requires the brain to separate a new stimulus from past sensory status. To clarify effects of past sensory status on processing in the human somatosensory cortex, brain responses to an abrupt change of intensity in a train of electrical pulses applied to the hand were recorded by magnetoencephalography (MEG). In Experiment 1, effects of the magnitude of deviance (1.0, 0.5, 0.3, 0.2, and 0.1 mA) between conditioning and test stimuli were examined. In Experiment 2, effects of the duration of the conditioning stimulus (3, 1.5, 1.0, and 0.5 s) were examined. The abrupt change in stimulus intensity activated the contralateral primary (cSI) and secondary somatosensory cortex (cSII). The amplitude of the cSI and cSII activity was dependent on not only the magnitude of the change in intensity but also the length of the conditioning stimulus prior to the change, suggesting that storage of prior tactile information was involved in generating these responses. The possibility that an activity of onset (with no conditioning stimulus) would be involved in the change-related activity was also discussed.

Selective Stimulation of C Fibers by an Intra-Epidermal Needle Electrode in Humans

We recorded evoked potentials (EPs) induced by intra-epidermal electrical stimulation using a needle electrode with specific parameters. We identified the fibers activated by this specific stimulation by assessing the conduction velocity (CV) of the peripheral nerve. The EPs were recorded from the Cz electrode (vertex) of the International 10-20 system in ten healthy male subjects. The dorsum of the left hand and forearm were stimulated with an intensity of 0.01 mA above the sensory threshold. The mean P1 latency of EPs for the hand and forearm were 1007 ± 88 and 783 ± 80 ms, respectively, and the CV estimated from the latency of P1 was 1.5 ± 0.7 m/s. The CV indicated that the fibers activated by the stimulation were C fibers. Since the method of stimulation is convenient and non-invasive, it should be useful for investigating the functions of small fibers.

The effect of water immersion on short-latency somatosensory evoked potentials in human

BackgroundWater immersion therapy is used to treat a variety of cardiovascular, respiratory, and orthopedic conditions. It can also benefit some neurological patients, although little is known about the effects of water immersion on neural activity, including somatosensory processing. To this end, we examined the effect of water immersion on short-latency somatosensory evoked potentials (SEPs) elicited by median nerve stimuli. Short-latency SEP recordings were obtained for ten healthy male volunteers at rest in or out of water at 30°C. Recordings were obtained from nine scalp electrodes according to the 10-20 system. The right median nerve at the wrist was electrically stimulated with the stimulus duration of 0.2 ms at 3 Hz. The intensity of the stimulus was fixed at approximately three times the sensory threshold.ResultsWater immersion significantly reduced the amplitudes of the short-latency SEP components P25 and P45 measured from electrodes over the parietal region and the P45 measured by central region.ConclusionsWater immersion reduced short-latency SEP components known to originate in several cortical areas. Attenuation of short-latency SEPs suggests that water immersion influences the cortical processing of somatosensory inputs. Modulation of cortical processing may contribute to the beneficial effects of aquatic therapy.Trial RegistrationUMIN-CTR (UMIN000006492)