Article

Transcranial magnetic stimulation disrupts eye-hand interactions in the posterior parietal cortex

Department of Exercise and Movement Science and Institute of Neuroscience, University of Oregon, Eugene, Oregon 97403-1240, USA.
Journal of Neurophysiology (Impact Factor: 3.04). 10/2000; 84(3):1677-80.
Source: PubMed

ABSTRACT Recent neurophysiological studies have started to shed some light on the cortical areas that contribute to eye-hand coordination. In the present study we investigated the role of the posterior parietal cortex (PPC) in this process in normal, healthy subjects. This was accomplished by delivering single pulses of transcranial magnetic stimulation (TMS) over the PPC to transiently disrupt the putative contribution of this area to the processing of information related to eye-hand coordination. Subjects made open-loop pointing movements accompanied by saccades of the same required amplitude or by saccades that were substantially larger. Without TMS the hand movement amplitude was influenced by the amplitude of the corresponding saccade; hand movements accompanied by larger saccades were larger than those accompanied by smaller saccades. When TMS was applied over the left PPC just prior to the onset of the saccade, a marked reduction in the saccadic influence on manual motor output was observed. TMS delivered at earlier or later periods during the response had no effect. Taken together, these data suggest that the PPC integrates signals related to saccade amplitude with limb movement information just prior to the onset of the saccade.

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    • "Wilmut et al. [34] tested the effect of producing saccades on the accuracy of sequential pointing and concluded that the role of ocular proprioception was far less important than the role of the feedforward system that is activated when an eye movement is initiated. Van Donkelaar et al. [35] provided even more direct evidence. The influence of decorrelating eye and hand movement start points (see Section 1) on hand movement amplitude is significantly reduced by transcranial magnetic stimulation over the posterior parietal cortex when stimulation is delivered 0–100 ms prior to saccade onset. "
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    • "Finally, also the spatial pattern of the observed TMS effects (impact on the aIPS and aSMG but not on more posterior control sites) argues against putative TMS effects on saccades as a large body of literature shows that more posterior parts of the PPC are involved in saccade processing (Simon et al. 2002; Konen et al. 2004). The TMS studies in this field always tested more posterior positions compared with our sites and offer inconsistent results on whether left PPC TMS does affect saccades processing (Van Donkelaar et al. 2000; Yang and Kapoula 2004). Desmurget et al. (1999) were the only group to date demonstrating that TMS over the left IPS largely disturbed online corrections in a visually perturbed reaching paradigm. "
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