FIELDS IN HUMAN MOTOR AREAS INVOLVED IN PREPARATION FOR REACHING, ACTUAL REACHING, AND VISUOMOTOR LEARNING - A POSITRON EMISSION TOMOGRAPHYSTUDY

The purpose of this study was to examine the functional organization o f motor cortices in the human brain involved in reaching and visuomoto r learning. All subjects were asked to learn the positions of seven ci rcular targets projected on a screen. Each time the targets were turne d off, they were required to close their eyes and keep them closed, an d, after a delay, to point to the center of the targets in a prescribe d order using their right hand. The regional cerebral blood flow (rCBF ) was measured with O-15-butanol and positron emission tomography in 2 0 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 consti tuted the preparation group in which rCBF was measured in the delay pe riod between target exposure and actual reaching. Individual subtracti on 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, cort ical fields were activated in the left primary motor area (Mi) and the left premotor area (PMA). Within M1, fields active in the delay phase s were adjacent to the fields active only during actual reaching movem ents. During the course of learning, additional fields of activity app eared in both M1 and PMA. The results indicate that three types of fie lds occur in M1 and PMA: (I)fields directly engaged in the efferent co ntrol of peripheral muscle contraction, (2) fields engaged in preparat ory activity for reaching, and (3) fields appearing after learning of the task has taken place.