Programs for action in superior parietal cortex: a triple-pulse TMS investigation

Converging evidence from neurological patients and functional brain imaging studies strongly supports the notion that the posterior parietal cortex (PPC), especially in the left hemisphere, plays a critical role in both the programming (i.e., setting the initial movement parameters of the reach) and the online control of goal-directed reaching movements. Importantly, however, there is no clear consensus on how different subregions within the PPC contribute to the programming and online control of reaching. In the current study, we investigated the role of the inferior (IPL) and superior (SPL) parietal lobules in reach programming using MRI-guided event-related transcranial magnetic stimulation (TMS). Specifically, we applied triple-pulse (tp) TMS to either the left IPL or the left SPL at different time points during reaching movements either at target onset (programming) or at movement onset (online control) while participants (n=16) made pointing movements to targets in the periphery without visual feedback of the moving hand. Stimulating the SPL but not the IPL resulted in a significant increase in endpoint errors when tp-TMS was applied during the programming phase compared to the online control phase. In short, these data demonstrate that the SPL plays a critical role in real-time movement programming.