FUNCTIONAL-ANATOMY OF REACHING AND VISUOMOTOR LEARNING - A POSITRON EMISSION TOMOGRAPHY STUDY

The purpose of this study was to identify the functional cortical fiel ds involved in reaching for targets in extrapersonal space, and to ide ntify the specific fields representing visual target information in lo ng-term memory. Ten healthy subjects were asked to learn the positions of seven circular targets that were repeatedly projected on a screen. The regional cerebral blood Row was measured with positron emission t omography during a rest state, at an early learning stage, at a later learning stage, and finally at 30 min after the course of learning had been completed. Mean rCBF change images for each task minus rest were calculated and fields of significant rCBF changes were identified. In all three task states, cortical fields were consistently activated in the left motor and premotor areas, the posterior part of the superior parietal lobule, and the right angular gyrus. When learning of the ta rget positions had been achieved, additional fields appeared bilateral ly in the posterior part of the superior parietal lobule, the right su perior occipital gyrus, the left motor and premotor areas, the medial aspect of the superior frontal gyrus, the postcentral gyrus, the super ior part of the cuneus, the inferior part of the angular gyrus, and th e anterior part of the insula. The results indicate that there are at least two different types of functional fields in the posterior part o f the superior parietal lobule; one is active during reaching for the targets when guided by internal representations of target positions; t he other likely represents the storage sites of visual target informat ion that is addressed in long-term memory.