Functional MRI Study of Posterior Parietal Cortex in Visuomotor Tasks

Abstract

The posterior parietal cortex is known to be involved in visuomotor task processing. Unsolved question are 1) whether a special cortical network is implied in pointing tasks or the same network is shared by other tasks with similar visual input and motor output 2) is there a hemispheric specialization in these treatments? Axial MR images were acquired in eight right-handed volunteers, using EPI sequence. Behavioral conditions were designed to perform two visiomotor tasks: a) pointing to a visual target, with the right or left hand; b) spatial detection of the visual target. Both tasks shared the same retinal input and motor output. The visual stimuli were generated by a computer and projected on a screen. Data processing included conditioned analysis and inter-subject comparison of different task activation extent and overlap in different cortical regions. Both tasks activated the same fronto-parietal network. Within this network, there was a significant cortical activation overlap between the pointing tasks performed with either hands, suggesting that a special treatment may be performed by the left parietal cortex for pointing tasks. An overlap between the detection task either with the right or the left hand was found in the right parietal cortex. Different visuomotor tasks involving the same reference frame transformations are performed by the same fronto-parietal network. The right parietal cortex may be specifically involved in detection tasks whereas the left parietal cortex would be specifically implied in processing of pointing tasks. These results are consistent with neuropsychological evidence from patients with parietal lesions.