TEMPORAL STRUCTURE OF IMPLICIT MOTOR IMAGERY IN VISUAL HAND-SHAPE DISCRIMINATION AS REVEALED BY MEG

WE investigated the spatio-temporal brain activity on the time scale o f several milliseconds related to the mental rotation task requiring j udgements of hand orientation, using a whole-cortex MEG (magnetoenceph alography) system. Neuronal activity in the visual cortex was observed similar to 100-200 ms from stimulus onset, and that in inferior parie tal lobe followed (after 200 ms). Both of these activities showed a co ntralateral dominance to visual stimulus hemifield. Premotor activity started later than the inferior parietal lobe activity, and these acti vities partially overlapped. Activity in primary motor and/or motosens ory areas was observed in some subjects. The whole-cortex neuromagneti c measurements provided the time course of activity in the human brain associated with the implicit motor imagery: visual cortex --> inferio r parietal lobe <-> premotor cortex. This process is considered to be the transformation process of retinotopic locations into a body-center ed reference frame necessary for the mental rotation task. (C) 1998 Ra pid Science Ltd.