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Cerebral Cortex Advance Access published online on January 10, 2007
Cerebral Cortex, doi:10.1093/cercor/bhl137
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© The Author 2007. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Human Parietal "Reach Region" Primarily Encodes Intrinsic Visual Direction, Not Extrinsic Movement Direction, in a Visual–Motor Dissociation Task

Juan Fernandez-Ruiz1,2,3, Herbert C. Goltz1,4,5, Joseph F. X. DeSouza1,3, Tutis Vilis1,6 and J. Douglas Crawford1,3,7

1 Canadian Institutes of Health Research Group on Action and Perception, 2 Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, México, 3 Centre for Vision Research, York University, Toronto, Ontario, Canada M3J 1P3, 4 Imaging Research Labs, Robarts Research Institute, London, Ontario N6A 5K8, Canada, 5 Department of Psychology, 6 Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada N6A 5C1, 7 Department of Psychology, York University, Toronto, Ontario, Canada M3J 1P3

Address correspondence to Dr J. Douglas Crawford, York Centre for Vision Research, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3. Email: jdc{at}yorku.ca.

Posterior parietal cortex (PPC) participates in the planning of visuospatial behaviors, including reach movements, in gaze-centered coordinates. It is not known if these representations encode the visual goal in retinal coordinates, or the movement direction relative to gaze. Here, by dissociating the intrinsic retinal stimulus from the extrinsic direction of movement, we show that PPC employs a visual code. Using delayed pointing and event-related functional magnetic resonance imaging, we identified a cluster of PPC regions whose activity was topographically (contralaterally) related to the direction of the planned movement. We then switched the normal visual–motor spatial relationship by adapting subjects to optical left/right reversing prisms. With prisms, movement-related PPC topography reversed, remaining tied to the retinal image. Thus, remarkably, the PPC region in each hemisphere now responded more for planned ipsilateral pointing movements. Other non-PPC regions showed the opposite world- or motor-fixed pattern. These findings suggest that PPC primarily encodes not motor commands but movement goals in visual coordinates.

Key Words: pointing • precuneus • reaching • reversing prism adaptation • visuomotor learning • visuomotor transformation


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