Brain activation related to the change between bimanual motor programs

By using positron emission tomography, we aimed to identify cerebral foci o f neuronal activation associated with the initiation of a specific motor pr ogram. To that end, a state of repeatedly alternating in- and antiphase of bimanual flexion and extension movements was compared with similar movement responses except phase changing. This comparison provided the opportunity to eliminate confounding effects of attention and simple movements. Change between the two bimanual motor programs was related with activation at the posterior border of the left angular gyrus, the right precuneus, and the ri ght premotor and right medial prefrontal cortex. In a subsequent experiment , with attention and random movements as additional variables, activation a t the posterior border of the left angular gyrus was found at the same sign ificance level. This posterior parietal activation may indicate an equivale nce with the coding of intention in monkey posterior parietal cortex. Lesio n of the left posterior parietal cortex in human gives rise to left-right d isorientation and ideomotor apraxia. Our results may support the view that these symptoms reflect the inability to transpose a motor plan to the repre sentation of a personal body scheme. Activation of the right premotor and r ight medial prefrontal cortex was related both to the change between motor programs and to the condition with strictly regular movement in which no ad ditional responses were made to randomly presented signals. This is consist ent with the concept that motor preparation is associated with both the sel ection of internally instructed movements and the suppression of irrelevant environmental stimuli. (C) 1999 Academic Press.