Automatic activation in the human primary motor cortex synchronized with movement preparation

The human primary motor cortex during a unilateral finger reactive movement to visual stimuli was examined by magnetoencephalography (MEG) measurement . The brain activity related to movement execution (the motor activity cont ralateral to the movement side) was estimated based on movement onset condi tions and reaction times. The movement onset conditions were: (1) a simple reaction time task with a visual stimulus, (2) a Go/NoGo task with differen t colored stimuli and (3) a Go/NoGo task with different position stimuli. D ipole source estimation was done, and the time course of the motor activity was calculated. The results showed that not only the visual response but a lso the contralateral motor activity was evoked by the stimulus in all case s, and even when the NoGo stimulus was given. The motor activity in the pri mary motor cortex was conjectured to consist of two dominant components: th e first component for the movement preparation and the second component for the movement execution. Because the first component happened with a consta nt delay time from the stimulus even in the NoGo case, the first component, coming through a fast pathway for signals from visual stimulus processing to the motor cortex without any intervening cognitive processing, was conje ctured to make the motor cortex prepare for the forthcoming movement onset automatically regardless of the stimulus instruction. (C) 1999 Elsevier Sci ence B.V. All rights reserved.