In monkeys, the anterior bank of the intraparietal sulcus (AIP) is involved in visually guided hand movements that are relevant to grasping objects. By contrast, its caudal bank (CIP) responds to three-dimensional surface orientation. On the basis of these findings, it has been proposed that CIP conveys spatial information to AIP, affecting motor output. Now, Shikata et al. report that the equivalent areas in the human brain show a similar division of labour, and suggest that these regions functionally interact during visually guided hand movements.

Using event-related functional imaging, the authors measured AIP and CIP activation in three different tasks: discrimination of surface orientation, imagination of the necessary movement to grasp a surface of a specific orientation, and execution of the actual movement. They found that, whereas CIP activation was similar in the three tasks, AIP activation was strongest when the movement was executed and weakest when the subject simply discriminated surface orientation. As Shikata et al. had previously shown that performance modulates CIP activity in the surface orientation task (its activation is stronger in successful trials), the authors now conclude that the functional dissociation between AIP and CIP originally observed in monkeys is also present in the human brain.

Although these findings are consistent with the idea that CIP might send information to AIP during visually guided hand movements, the rigorous testing of this idea will require the use of additional techniques such as transcranial magnetic stimulation during the performance of similar behavioural tasks.