Abstract
The purpose of this study was to examine the functional organization of motor cortices in the human brain involved in reaching and visuomotor learning. All subjects were asked to learn the positions of seven circular targets projected on a screen. Each time the targets were turned off, they were required to close their eyes and keep them closed, and, after a delay, to point to the center of the targets in a prescribed order using their right hand. The regional cerebral blood flow (rCBF) was measured with 15O-butanol and positron emission tomography in 20 subjects during a rest state, an initial learning stage, and a later learning stage. Ten subjects constituted the reaching group in which rCBF was measured during actual reaching; the 10 other subjects constituted the preparation group in which rCBF was measured in the delay period between target exposure and actual reaching. Individual subtraction images (each stage minus rest) were calculated and transformed into a standard size and shape brain image by the adjustable computerized brain atlas and averaged, after which significant changes of rCBF were identified. In all reaching and preparation for reaching phases, cortical fields were activated in the left primary motor area (M1) and the left premotor area (PMA). Within M1, fields active in the delay phases were adjacent to the fields active only during actual reaching movements. During the course of learning, additional fields of activity appeared in both M1 and PMA. The results indicate that three types of fields occur in M1 and PMA: (1) fields directly engaged in the efferent control of peripheral muscle contraction, (2) fields engaged in preparatory activity for reaching, and (3) fields appearing after learning of the task has taken place.