中川 誠司

In recent years, techniques have been developed for estimating internal electrical sources in the human brain from measurements of magnetic fields (MEG). In this study, we investigate how to estimate spatially distributed sources, since this information is important for analyzing the higher functions of the human brain. We used a 64-channel whole-head-type SQUID system to record MEG activities evoked by visually cognitive tasks. Three kinds of stimuli were presented: English words, nonsense words, and random dot patterns. Spatially distributed internal sources with latencies between 320 and 420 ms were estimated by using the sub-optimal least-squares subspace scanning technique. The estimated sources were located in the frontal region for random-dot stimuli, the left temporal region for nonsense-word stimuli, and the right postero-temporal region in addition to the other regions for English-word stimuli.

Visually evoked magnetoencephalograms (MEGs) associated with a delayed-match paradigm were measured to obtain functional information related to short-term memory processes. A delayed-match paradigm was introduced. The paradigm consists of a four-color-stimuli; a pair of circles with four differently-colored regions. The subjects retain the first image (Sample) until the second image (Test) appears. The MEGs were measured by a 122-channel whole-head-type SQUID system. A DC-like slow wave was observed at the period between latencies of 900 and 1500 msec during the short-term memory task. The source localization of the DC-like slow wave was estimated. The estimated sources were localized either in the occipital or postero-temporal region.

In this study, we investigate an estimation of internal sources with poor information about their source profile, which is important in order to analyze the higher functions of the human brain. We used a 64-channel whole-head-type SQUID system to record MEG activities evoked by visually cognitive tasks. Three kinds of stimuli were presented: English words, nonsense words, and random dot patterns. Spatially distributed internal sources with latencies between 320 and 420 msec were estimated by using a sub-optimal lease-squares subspace scanning technique. From three subjects data, the following results of distributed source estimations were shown: English words stimuli activated large area, the left temporal region, the parietal and right postero-temporal region, nonsense words activated the parertal region, random dot patterns activated the frontal region.

Visually evoked magnetoencephalograms (MEGs) associated with a delayed-match paradigm were measured to obtain functional information related with short-term memory processes. A delayed-match paradigm was introduced. The paradigm consists of four-color stimuli; a pair of circles with four differently colored regions. The MEGs were measured by a 122-channel whole-head-type SQUID system. A DC-like slow wave was observed at the period between latencies of 900 and 1,500 ms during the short-term memory task. The source localization of the DC-like slow wave was estimated. The estimated sources were localized either in the occipital or posterotemporal region.

Visually evoked magnetoencephalograms (MEGs) associated with a delayed-match paradigm were measured to obtain functional information related to shortterm memory processes. A delayed-match paradigm was introduced. The paradigm consists of a four-color-stimuli; a pair of circles with four differently-colored regions. The subjects retain the first image (Sample) until the second image (Test) appears. The MEGs were measured by a 122-channel whole-head-type SQUID system. A DC-like slow wave was observed at the period between latencies of 900 and 1500 msec during the short-term memory task. The source localization of the DC-like slow wave was estimated. The estimated sources were localized either in the occipital or postero-temporal region.

We observed the brain electrical activities associated with verbal cognitive processes by measuring both EEGs and MEGs evoked by visually cognitive tasks. English words, nonsense words and random dots were presented. We discussed the source estimation at a latencies of 150 msec and 360 msec using MEG data. At 150 msec, two equivalent current dipoles are localized in or near the primary visual cortex. The dipole sources for recognition of English words at 360 msec were estimated in both hemispheres, and the dipole moment in the left-hemisphere was larger than the dipole moment of the right hemisphere. However, we could not find sources common to all subjects.