EVIDENCE FOR A DORSOMEDIAL PARIETAL SYSTEM INVOLVED IN MENTAL TRANSFORMATIONS OF THE BODY

1. The neural systems underlying body-space mental representation were studied by measuring changes in regional cerebral blood flow (CBF) wi th positron emission tomography in human subjects. 2. The experimental paradigm involved identification of the left or the right hand of the experimenter presented in different orientations on the palm of the s ubject's right hand. The subjects were required to decide whether it w as the left or the right hand that was presented. To perform this task , the subjects had to move mentally the position of their own arm to a dopt that of the experimenter's arm. The control condition involved th e same type of tactual stimulation without the requirement of mental t ransformations of the subject's body position. The distribution of CBF was measured by means of the water bolus (H2O)-O-15 methodology durin g the performance of these tasks. 3. Comparison of the distribution of CBF between the experimental and control tasks was carried out to rev eal changes specific to the mental transformations of the subject's bo dy. Significant blood flow increases were observed in the caudal super ior parietal cortex, including the intraparietal sulcus, and the adjac ent medial parietal cortex. These Endings demonstrated that there is a dorsomedially directed parietal system underlying mental transformati ons of the body in interactive relation with external space.