REPRESENTATIONS OF GRAPHOMOTOR TRAJECTORIES IN THE HUMAN PARIETAL CORTEX - EVIDENCE FOR CONTROLLED PROCESSING AND AUTOMATIC PERFORMANCE

The aim of this study was to identify the cerebral areas activated dur ing kinematic processing of movement trajectories. We measured regiona l cerebral blood flow (rCBF) during learning, performance and imagery of right-hand writing in eight right-handed volunteers. Compared with viewing the writing space, increases in rCBF were observed in the left motor, premotor and frontomesial cortex, and in the right anterior ce rebellum in all movement conditions, and the increases were related to mean tangential writing velocity. No rCBF increases occurred in these areas during imagery. Early learning of new ideomotor trajectories an d deliberately exact writing of letters both induced rCBF increases in the cortex lining the right intraparietal sulcus. In contrast, during fast writing of overlearned trajectories and in the later phase of le arning new ideograms the rCBF increased bilaterally in the posterior p arietal cortex. Imagery of ideograms that had not been practised previ ously activated the anterior and posterior parietal areas simultaneous ly. Our results provide evidence suggesting that the kinematic represe ntations of graphomotor trajectories are multiply represented in the h uman parietal cortex. It is concluded that different parietal subsyste ms may subserve attentive sensory movement control and whole-field vis uospatial processing during automatic performance.