Akira Hashizume

Anticipation of affective images and event-related desynchronization (ERD) of alpha activity : An MEG study

We investigated the event-related power decrease (event-related desynchronization: ERD) of the alpha bands associated with the anticipation of affective images. Participants (n=19) were presented with emotionally positive or negative images under different anticipatory conditions, and their brain responses were recorded using magnetoencephalography (MEG). In the Affective Cue conditions, the cue stimulus indicated the emotional valence (positive or negative) of the image. In the Null Cue condition, the cue stimulus did not include any information about the valence of the image, and in the No Cue condition, the affective image was presented without a preceding cue. The cues in the affective and null conditions were followed by emotional images. During the anticipation period for the affective image, the alpha ERD preceding an anticipated negative image was larger than that preceding an anticipated positive image; this effect had an occipital dominance. Furthermore, during the anticipation period, the lower-2-alpha ERD of the right frontal area showed the same result. These results demonstrate that anticipation of negative stimuli induced alpha ERD in both the visual and the right frontal cortex, indicating that top-down modulation may be provided by the right frontal cortex to the visual cortex.

Neuromagnetic beta oscillation changes during motor imagery and motor execution of skilled movements.

We showed the differences in brain activities during motor imagery and motor execution when performing single skilled movements using magnetoencephalography. The tasks included finger tapping and chopstick usage with the dominant or nondominant hand. Chopstick usage with the nondominant hand was an unfamiliar task and required higher skill. Neuromagnetic data were processed by fast Fourier transformation, and &bgr; band event-related synchronization was evaluated. Beta oscillation changes were observed in the right and left sensorimotor cortices during both tasks; however, the ipsilateral changes were smaller during motor imagery than during motor execution. These results suggest that motor imagery of skilled movement tasks causes a smaller neuronal burden in the sensorimotor cortex.

Effects of movement on somatosensory N20m fields and high-frequency oscillations.

Somatosensory evoked fields were recorded to determine the effects of movement and attention on high-frequency oscillations during active finger movements of the ipsilateral and contralateral sides in response to electrical stimulation of the median nerve. A whole-scalp neuromagnetometer was used to record somatosensory evoked fields from eight subjects following electric median nerve stimulation at the wrist. The following three sessions were performed: (1) rest, (2) movement of fingers on the ipsilateral in response to stimulation and (3) movement of fingers on the contralateral in response to stimulation. The somatosensory evoked fields with a wide-bandpass (0.1–1000 Hz) were recorded. High-frequency oscillations and N20m were separated by subsequent high-pass (> 300 Hz) and low-pass (< 300 Hz) filtering. The maximum amplitude of high-frequency oscillations decreased during finger movements accompanying a decrease in somatosensory N20m dipole strength. Activation of the motor cortex appeared to suppress both the amplitude of high-frequency oscillations and the N20m dipole strength.

The respiratory cycle modulates brain potentials, sympathetic activity, and subjective pain sensation induced by noxious stimulation

To test the hypothesis that a respiratory cycle influences pain processing, we conducted an experimental pain study in 10 healthy volunteers. Intraepidermal electrical stimulation (IES) with a concentric bipolar needle electrode was applied to the hand dorsum at pain perceptual threshold or four times the perceptual threshold to produce first pain during expiration or inspiration either of which was determined by the abrupt change in an exhaled CO2 level. IES-evoked potentials (IESEPs), sympathetic skin response (SSR), digital plethysmogram (DPG), and subjective pain intensity rating scale were simultaneously recorded. With either stimulus intensity, IES during expiration produced weaker pain feeling compared to IES during inspiration. The mean amplitude of N200/P400 in IESEPs and that of SSR were smaller when IES was applied during expiration. The magnitude of DPG wave gradually decreased after IES, but a decrease in the magnitude of DPG wave was less evident when IES was delivered during expiration. Regardless of stimulus timing or stimulus intensity, pain perception was always concomitant with appearance of IESEPs and SSR, and changes in DPG. Our findings suggest that pain processing fluctuates during normal breathing and that pain is gated within the central nervous system during expiration.

Gradient magnetic-field topography for dynamic changes of epileptic discharges

We developed gradient magnetic-field topography (GMFT) for magnetoencephalography (MEG). We plotted the Euclidean norms of gradient magnetic fields occurring at the centers of 102 sensors onto 49-point grids and projected these norms onto the MRI brain surface of a 12-year-old boy who presented with neocortical epilepsy secondary to a left temporal tumor. The peak gradient magnetic field located posterior to the tumor and correlated to MEG dipoles. The gradient magnetic field propagated to the temporo-parietal region and corresponded with spike locations on electrocorticography. GMFT revealed the location and distribution of spikes while avoiding the inverse problem.

Gradient magnetic-field topography reflecting cortical activities of neocortical epilepsy spikes

PURPOSE To compare and validate the gradient magnetic-field topography (GMFT) method of current source localization for understanding epileptic zones against equivalent current dipole (ECD) and intracranial video-EEG (IVEEG) data in patients with intractable neocortical epilepsy. METHODS We used retrospective data from eight patients to determine GMFT at onset (O) and peak (P) of interictal magnetoencephalography (MEG) spikes and mapped GMFT(O) and GMFT(P) locations and distributions using 12 zones in unilateral hemisphere. We compared GMFT with ECD, ictal onset zones (IOZ) and interictal zones on IVEEG, and seizure outcomes. RESULTS We projected GMFT(Os) and (Ps) for all spikes on volume-rendered brain surfaces. We localized ECDs for 6-61% of spikes (mean, 28.4%). GMFT(Ps) (mean, 10.3 zones) extended over more zones than GMFT(Os) (6.3 zones) for each spike (p<0.01). The ECD distributions (2.3 zones) were almost equal to the zones of IOZ and surgical areas. GMFT(O) localizations distributed much more extensively than IOZs and surgical areas in three patients with residual seizures comparing with those in five seizure-free patiens. CONCLUSION We validate the potential of GMFT to study the distribution of MEG spikes. GMFT has an advantage in analyzing the cortical activity and propagation from MEG spikes in neocortical epilepsy.

Difference in somatosensory evoked fields elicited by mechanical and electrical stimulations: Elucidation of the human homunculus by a noninvasive method.

We recently recorded somatosensory evoked fields (SEFs) elicited by compressing the glabrous skin of the finger and decompressing it by using a photosensor trigger. In that study, the equivalent current dipoles (ECDs) for these evoked fields appeared to be physiologically similar to the ECDs of P30m in median nerve stimulation. We sought to determine the relations of evoked fields elicited by mechanically stimulating the glabrous skin of the great toe and those of electrically produced P40m. We studied SEFs elicited by mechanical and electrical stimulations from the median and tibial nerves. The orientations of dipoles from the mechanical stimulations were from anterior‐to‐posterior, similar to the orientations of dipoles for P30m. The direction of the dipole around the peak of N20m from median nerve electrical stimulation was opposite to these directions. The orientations of dipoles around the peak of P40m by tibial nerve stimulation were transverse, whereas those by the compression and decompression stimulation of the toe were directed from anterior‐to‐posterior. The concordance of the orientations in ECDs for evoked fields elicited by mechanical and electrical stimulations suggests that the ECDs of P40m are physiologically similar to those of P30m but not to those of N20m. The discrepancy in orientations in ECDs for evoked field elicited by these stimulations in the lower extremity suggests that electrical and compression stimulations elicit evoked fields responding to fast surface rubbing stimuli and/or stimuli to the muscle and joint. Hum. Brain Mapping 24:274–283, 2005.

Somatosensory mechanical response and digit somatotopy within cortical areas of the postcentral gyrus in humans: an MEG study.

Somatosensory evoked fields in response to compression (termed as Co) and decompression (termed as De) of glabrous skin (D1, thumb; D2, index finger; D5, little finger) were recorded. Although estimated equivalent current dipoles (ECDs) following stimulation of D1 and D5 were larger, but not significantly larger, in decompression than in compression, those of D2 were significantly larger (P = 0.035). The ECDs were located in the postcentral gyrus in the order of D5De, D2De, and D1De medially, posteriorly, and superiorly in decompression but not in compression (z‐value, F = 2.692, P = 0.031). The average distance of ECDs between D1 and D5 was longer in decompression (12.8 ± 1.6 mm) than in compression (9.1 ± 1.6 mm). Our data suggest that the cortical response for the commonly used digit D2 is functionally different from those for other digits (D1 and D5) that the somatotopic variability is greater in compression. Hum Brain Mapp, 2013.

Human reactions to physical stimulus and the removal of such stimulus as recorded by magnetoencephalography

We studied the cortical evoked fields elicited by the examiners touch on glabrous skin of the subjects index finger. Two main components of evoked fields were elicited, and these dipoles were located in the primary somatosensory cortex contralateral to the side of the subjects index finger touched by the examiner. When the timing of removal of the examiners finger triggered the data acquisition using the photosensor, the strength of the dipole from early evoked fields was stronger than that from late ones. We showed that these evoked fields were elicited by removal and touch of the examiners finger respectively in response to the mechanical compression and decompression of the skin.

Enhanced Reactivity and Delayed Recovery of Sensorimotor Cortex in the Novelty Seeking Personality

Background: The novelty seeking (NS) personality trait is hypothesized to be associated with high cortical reactivity, poor inhibitory control and/or varied dopaminergic neurotransmission in the basal ganglia. After somatosensory stimulation, electrical oscillations in alpha and beta bands generated in the sensorimotor cortex show a short duration decrease (event-related desynchronization) and a subsequent increase (event-related synchronization) that is thought to reflect cortical activation and the inhibitory/recovery process, respectively. These oscillatory changes are also believed to be affected by the status of the basal ganglia and by dopaminergic functions. In the present study, we investigated the association between the NS personality trait and somatosensory oscillatory changes after median nerve stimulation assessed by magnetoencephalography. Methods: From 48 healthy subjects, we selected 14 high scorers and 14 age- and sex-matched low scorers on the NS dimension of the Temperament and Character Inventory. Magnetic fields were recorded while subjects received electrical stimulation of either the right or left median nerve with equal probability and with a randomized interstimulus interval. Frequency analysis was performed on the alpha and beta bands. Results: Compared with the low NS group, the high NS group showed larger magnitude of beta event-related desynchronization and larger latencies of the alpha and beta event-related synchronization. Conclusion: These results suggest that individuals with high degrees of the NS trait have greater reactivity and delayed recovery of the sensorimotor cortex in response to simple somatosensory stimulation. This may be significant for the understanding of their exploratory and impulsive behavior.