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J Neurophysiol (August 6, 2008). doi:10.1152/jn.90519.2008
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Submitted on April 30, 2008
Revised on June 29, 2008
Accepted on July 25, 2008

TMS OVER HUMAN DORSAL-LATERAL POSTERIOR PARIETAL CORTEX DISRUPTS INTEGRATION OF HAND POSITION SIGNALS INTO THE REACH PLAN

Michael Vesia1, Xiaogang Yan1, Denise Y. P. Henriques1, Lauren E. Sergio1, and J. Douglas Crawford1*

1 York University

* To whom correspondence should be addressed. E-mail: jdc{at}yorku.ca.

Posterior parietal cortex (PPC) has been implicated in the integration of visual and proprioceptive information for the planning of action. We previously reported that single-pulse transcranial magnetic stimulation (TMS) over dorsal-lateral PPC perturbs the early stages of spatial processing for memory-guided reaching. However, our data did not distinguish whether TMS disrupted the reach goal or the internal estimate of initial hand position needed to calculate the reach vector. To test between these hypotheses, we investigated reaching in six healthy humans during left and right parietal TMS while varying visual feedback of the movement. We reasoned that if TMS were disrupting the internal representation of hand position, visual feedback from the hand might still recalibrate this signal. We tested four viewing conditions: (i) final vision of hand position (FIN); (ii) full vision of hand position (FUL); (iii) initial and final vision of hand position (INI); and (iv) middle and final vision of hand position (MID). During the FIN condition, left parietal stimulation significantly increased endpoint variability, whereas right parietal stimulation produced a significant leftward shift, in both visual fields. However, these errors significantly decreased with visual feedback of the hand during both planning and control stages of the reach movement. These new findings demonstrate that (i) visual feedback of hand position during the planning and early execution of the reach can recalibrate the perturbed signal; and more importantly (ii) TMS over dorsal-lateral PPC does not disrupt the internal representation of the visual goal, but rather the reach vector, or more likely the sense of initial hand position that is used to calculate this vector.




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S. Ferraina, E. Brunamonti, M. A. Giusti, S. Costa, A. Genovesio, and R. Caminiti
Reaching in Depth: Hand Position Dominates over Binocular Eye Position in the Rostral Superior Parietal Lobule
J. Neurosci., September 16, 2009; 29(37): 11461 - 11470.
[Abstract] [Full Text] [PDF]




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