PET STUDY OF POINTING WITH VISUAL FEEDBACK OF MOVING HANDS

This study was conducted to determine where in the human brain visual feedback of hand movements is processed to allow accurate pointing. Re gional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) and H-2 O-15 in nine normal volunteers while performi ng one control and two reaching tasks. In all tasks, visual stimuli we re presented on a head mounted display (HMD). A target board was place d in front of the subjects bearing six red light-emitting diodes (LEDs ) aligned on a circle with a green LED at its center. The center green LED and one of the six red LEDs, randomly selected, were repeatedly s witched on and off, alternatively. In the control task, subjects were instructed to gaze at the lit LED. In the two reaching tasks, the reac hing with visual feedback (RwithF) task and the reaching without visua l feedback (RwithoutF) task, they had to point to the lit red LED with their right index fingers. In the RwithF task, their right hands were visible on the HMD before touching the target, whereas in the Rwithou tF task, they were not visible. For each subject, subtraction images o f each reaching task minus the control and the RwithF task minus the R withoutF task were calculated after transformation of PET images into the standard brain shape with an adjustable computerized brain atlas. These subtraction rCBF images were then averaged among the subjects, a nd significant changes of rCBF were identified. Significant increases in rCBF not only in the RwithF task minus control image but also in th e RwithF task minus the RwithoutF task image were observed in the supr amarginal cortex, the premotor cortex and the posterior cingulate cort ex of the left hemisphere, the caudate nucleus and the thalamus of the right hemisphere, and the right cerebellum and vermis. These results indicate that the supramarginal cortex, the premotor cortex, and the p osterior cingulate cortex of the left hemisphere and the cerebellum ar e involved in integrating visual feedback of hand movements and execut ion of accurate pointing.