中川 誠司

We previously investigated the effect of movement-associated intention on nervous activities using neurophysiologic indexes in order to estimate how movement is generated under expected or unexpected conditions. In this study, we measured magnetoencephalographic (MEG) signals during passive finger movement, and evaluated the effect of the existence of anticipation on cortical activities. The subjects were 10 right-handed healthy volunteers. The subjects anticipated the passive movement by receiving warning signals before the movement, and the passive movement was generated as the result of the subjects' anticipation. In the first experiment (Experiment I), a series of warning signals was presented to indicate the onset of passive movement. In the second experiment (Experiment II), a warning signal was given to indicate the direction of passive movement. The passive movement was lifting or lowering the right middle finger (only lifting was applied in Experiment I). Consequently, in Experiment I, for passive movement with a warning signal, MEG deflection before the movement and shortening of the peak latency with a reduction in the amplitude of somatosensory evoked field (SEF) components were observed, compared to values under the condition of no warning signal. However, in Experiment II, there was no change in peak latency, but reduction in the SEF amplitude under the conditions of a warning signal being given. The present results indicate a possibility that anticipation prior to the predictable passive movement modulated the cortical activities in physiological condition.

Auditory evoked magnetic fields in relation to the factor extracted from autocorrelation function (ACF) were examined by magnetoencephalography (MEG). In the first experiment, bandwidth of bandpass noises (BNs) was varied to control the peak amplitude of the ACF. Auditory evoked fields (AEFs) were recorded using a neuromagnetometer in a magnetically-shielded room. The results showed that the peak amplitude of N1m, which was found above the left and right temporal lobes around 100 ms after the stimulus onset, decreased with increasing bandwidth of the BN. In the second experiment, iterated rippled noise (IRN) was used. The IRN was produced by a delay-and-add algorithm applied to BN that was filtered between 400-2200 Hz. Each delay-and-add cycle is called iteration; the delay-and-add process increases the peak amplitude of the ACF. The results showed that the peak amplitude of N1m increased with increasing the number of iteration. These results clearly indicate that the peak amplitude of N1m increased with increasing the peak amplitude of ACF of the stimulus. Therefore, sounds that have more temporal regularity could lead to more cortical activity, which would cause an increase in the strength of the N1m response.

This paper described that the relationship between the eigenfrequencies of CT scanned realistic human head model and the subjective detecting pitch which is given by providing the bone-conducted ultrasound. Our goal is to develop the optimal bone-conducted ultrasonic hearing aid for profoundly hearing-impaired persons. An ascent of a speech intelligibility is the requirement of hearing aid. To improve it, the perception mechanism of the bone-conducted ultrasound must be clarified, but the conclusive agreement of it has not been reached yet, although many hypotheses were reported. The authors predict that the cochleae are related to the perception mechanism for bone-conducted ultrasound, since it has been verified that the auditory cortex responds to bone-conducted ultrasound by MEG study. And now, we are interested in the detecting pitch of bone-conducted ultrasound with no frequency-dependent. Thus, in this paper, waves propagating from the mastoid to both cochleae are numerically analyzed and the characteristics of transfer functions are estimated as a first step to clarifying the perception mechanism for detecting pitch of bone-conducted ultrasonic stimuli.

Auditory evoked magnetic fields in relation to the factor extracted from autocorrelation function (ACF) were examined by magnetoencephalography (MEG). In the first experiment, bandwidth of bandpass noises was varied to control the peak amplitude of the ACF. Auditory evoked fields were recorded using a magnetometer in a magnetically-shielded room. The results showed that the peak amplitude of N1m, which was found above the left and right temporal lobes around 100 ms after the stimulus onset, decreased with increasing bandwidth. In the second experiment, iterated rippled noise (IRN) was used. The IRN was produced by a delay-and-add algorithm applied to bandpass noise. The delay-and-add process increases the peak amplitude of the ACF, thus the pitch strength. The other settings for presenting the stimuli were the same as those used in the first experiment. The results showed that the peak amplitude of N1m increased with increasing the number of iteration. These results clearly indicate that the peak amplitude of N1m increased with increasing the peak amplitude of ACF of the stimulus. Therefore, sounds that have more temporal regularity could lead to more cortical activity, which would cause an increase in the strength of the N1m response.