The influence of lorazepam on somatosensory-evoked fast frequency (600 Hz)activity in MEG

The generators of high frequency bursts (600-Hz activity) detected at the p arietal scalp over the primary somatosensory cortex after electrical stimul ation of peripheral nerves are not yet known. We investigated the influence of benzodiazepine on the somatosensory-evoked 600-Hz activity by means of neuromagnetic measurements and source analysis. After oral administration o f lorazepam, the latency of the 600-Hz burst activity was increased; specif ically later peaks were delayed more than earlier peaks. In contrast, the l atency of the concurrent primary cortical low frequency response (N20m) was not significantly changed. The source strengths of both N20m and 600-Hz bu rsts were significantly increased. Our results provide evidence for two com ponents of the 600-Hz activity with a different generator structure. (C) 20 00 Elsevier Science B.V. All rights reserved.