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Christopher L. Striemer, Philippe A. Chouinard, Melvyn A. Goodale; Plans for action in posterior parietal cortex: An rTMS investigation. Journal of Vision 2010;10(7):1096. doi: 10.1167/10.7.1096.
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Many theories of visuomotor control distinguish between the planning of a movement (i.e., programming the initial kinematic parameters), and the execution of the movement itself (so-called ‘online control’). Evidence from neurological patients and functional brain imaging studies strongly support the notion that the posterior parietal cortex (PPC; especially the left hemisphere) plays a critical role in the planning and execution of goal-directed movements. Importantly, however, there is no clear consensus on how different sub-regions within the PPC contribute to movement planning and execution. Some theories suggest that both planning and execution are carried out primarily within the superior parietal lobe (SPL), whereas others suggest that planning is carried out by inferior parietal lobe (IPL) and execution is carried out by the SPL. In the current study we investigated this question using MRI-image guided repetitive transcranial magnetic stimulation (rTMS; 3 pulses at 10Hz). Specifically, we applied rTMS to different sites within the left IPL (angular and supramarginal gyri) and the left SPL (anterior and posterior SPL) either at target onset (planning), or movement onset (execution), while participants (n=12) made open-loop pointing movements to targets in peripheral vision. Thus, participants had vision of their hand and the target during the planning phase; however, vision of the hand and the target were removed at movement onset. The results revealed a significant interaction between the site of rTMS stimulation and the time of rTMS delivery. This interaction was driven by a significant increase in movement endpoint error when rTMS was applied during movement planning compared to execution in the SPL compared to both the IPL and sham stimulation. In short, these data are consistent with the idea that the SPL plays a crucial role in the planning (i.e., programming) of goal directed movements.
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