Functional anatomy of reaching and visuomotor learning: a positron emission tomography study

The purpose of this study was to identify the functional cortical fields involved in reaching for targets in extrapersonal space, and to identify the specific fields representing visual target information in long-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 flow was measured with positron emission tomography 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 target positions had been achieved, additional fields appeared bilaterally in the posterior part of the superior parietal lobule, the right superior occipital gyrus, the left motor and premotor areas, the medial aspect of the superior frontal gyrus, the postcentral gyrus, the superior part of the cuneus, the inferior part of the angular gyrus, and the anterior part of the insula. The results indicate that there are at least two different types of functional fields in the posterior part of the superior parietal lobule; one is active during reaching for the targets when guided by internal representations of target positions; the other likely represents the storage sites of visual target information that is addressed in long-term memory.