A comparison of the dorsomedial and the dorsolateral reach-to-grasp pathways' roles in response to virtual visual perturbations of object goal.

Traditional research approaches to the reach-to-grasp movement have employed real-world perturbations involving physical objects. Recent technological advances provide new avenues for the investigation of sensorimotor control including the use of Virtual Reality Environments (VE). In this study, we used an immersive VE to produce compelling perturbations of target object size and position and Transcranial Magnetic Stimulation (TMS) to probe the neural bases of compensatory responses during grasping movements. Extensive research has identified a Dorsolateral (DL) and a Dorsomedial (DM) pathway as the likely neural bases for the sensorimotor coordination underlying grasping movements. In order to test the causal involvement of the parietal and premotor nodes of both pathways, we implemented visual perturbations of object size and distance at two different latencies (100 and 300 ms after movement onset) with concurrent TMS in a fully randomized design. The kinematic profiles of the grasping movements exhibited clear effects of the visual perturbations, particularly the late ones. We found that TMS stimulation of aIPS during the late perturbation of object size modified the timing of aperture closing. Similarly, TMS to PMv during the late perturbation of object distance reduced transport velocity during the compensatory double-peak. Our results support the involvement of the DL pathway when quick modifications including complex digit control are required. Against our expectations, sudden changes in target position did not elicit activity in the DM pathway. This study supports the notion that VE can be successfully employed for the study of the neural substrates of motor control.