Biomedical subjects

Takushi Shirai

Publications and source records attributed to Takushi Shirai.

6 recordsLinked to original sources

PubMed2005

Activation of human SII cortex during exploratory finger movement and hand clenching tasks.

We used electric median nerve stimuli to elucidate the functional properties of neurons in the human secondary somatosensory cortex during exploration of small objects and muscle contraction. Somatosensory evoked fields were recorded from nine healthy subjects with a 204-channel neuromagnetometer. Electrical stimuli were applied once every 3 s to the left median nerve at the wrist. The conditions during the stimulation were rest (control session), exploration of small objects (exploration session) and clenching the hand while the wrist was being electrically stimulated (clench session). The strengths of equivalent current dipoles of evoked fields from the secondary somatosensory cortex were increased during the exploration session, but those of evoked fields were decreased by the clench session.

Adult↗

PubMed2005

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.

Adult↗

PubMed2004

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

We studied the cortical evoked fields elicited by the examiner's touch on glabrous skin of the subject's 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 subject's index finger touched by the examiner. When the timing of removal of the examiner's 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 examiner's finger respectively in response to the mechanical compression and decompression of the skin.

Adult↗

PubMed2004

Disinhibition of the somatosensory cortex in cervical dystonia-decreased amplitudes of high-frequency oscillations.

OBJECTIVE: To determine whether patients with cervical dystonia have electrophysiological signs of disinhibition in the somatosensory cortex by recording high-frequency oscillations (HFOs) in somatosensory evoked potentials (SEPs). METHODS: HFOs were recorded in 13 patients and 10 age-matched control subjects, and the data were analyzed statistically by paired comparison and by Pearson's correlation. RESULTS: In patients with cervical dystonia, the early part of HFOs showed a significant decrease in amplitude, and the amplitude ratios of both early and late parts of HFOs/N20 potential were also significantly decreased. The amplitudes of HFOs and N20 potential were linearly correlated in the control subjects but not in dystonia patients. CONCLUSIONS: Patients with cervical dystonia may suffer from a disturbance of inhibition in the sensory cortex. This disturbance is reflected by decreased HFO amplitude, representing decreased activities of inhibitory interneurons in area 3b.

Adult↗

PubMed2004

[Somatosensory evoked potentials/fields--exploration of brain function].

We have summarized the history of electroencephalography(EEG) since 1875, when a paper by Richard Caton was published describing the first EEG recordings in animals. Somatosensory evoked potentials (SEPs) were recorded by George Dawson in 1951. Thereafter, SEPs were developed for clinical use with other evoked potentials such as auditory evoked potentials(VEPs). To understand evoked potentials, related mechanism of induction of far-fields-potentials(FFP) following stimulation of the median nerve has been discussed. SEPs consisted of P9, N9, N10, P11, N11, N13, P13, P14, N18, N20 and P20/P22. Scalp recorded P9 FFP arises from the distal portion of the branchial plexus as reflected by N9 stationary negative potential recorded over the stimulated arm. Cervical N11 and N13 arise from the root entry zone and dorsal horn, respectively. Scalp recorded P13, P14 and N18 FFP originate from the brainstem. In this communication, magnetoencephalography(MEG) and results of one of our recent studies on somatosensory evoked fields(SEFs) are also discussed. One of the important features of MEG is that magnetic signals detected outside the head arise mainly from cortical currents tangential to the skull. Since the net postsynaptic current follows the orientation of cortical pyramidal cells, the MEG signals mainly reflect activity of the fissural cortex, whereas radial current may remain undetected. In our study, we demonstrated SEFs elicited by compression and decompression of a subject's glabrous skin by a human operator. Their dipoles were tangentially oriented from the frontal lobe to parietal lobe.

Animals↗

PubMed2003

TH1-biased immunity induced by exposure to Antarctic winter.

BACKGROUND: Certain immune functions are known to be impaired in human beings exposed to Antarctic winter; in particular, decreased amounts of serum proinflammatory cytokines, such as TNF-alpha and IL-1, were noted. It is not known, however, whether this exposure has any effect on T-cell-mediated acquired immune functions. OBJECTIVES: This study aims to investigate whether exposure to Antarctic winter has any effect on T cell-dependent immune functions. METHODS: We assessed changes in various immunologic indicators, including serum levels of various cytokines, peripheral blood Valpha24Vbeta11 natural killer T cell numbers, and T(H)1/T(H)2 ratios of 40 Japanese personnel exposed to an Antarctic winter. Also, a 2-month inland traverse was executed during the isolation, and the effect on the above indicators was assessed. RESULTS: All subjects were healthy during the Antarctic isolation. The levels of serum TNF-alpha, IL-1Ra, IL-6, and IL-1beta were dramatically reduced and remained at low levels throughout the isolation. The decrease in the levels of TNF-alpha and IL-1Ra was more pronounced during the inland traverse than during the rest of the isolation. The percentage of Valpha24Vbeta11 natural killer T cells was significantly increased at the midpoint of the isolation. Most interestingly, T(H)1/T(H)2 ratio was increased significantly, and this T(H)1 bias was most prominent at the late point of the isolation. CONCLUSIONS: Exposure to an Antarctic winter appeared to induce T(H)1-skewed immunity in human beings.

Adult↗