Asymmetry of parietal interhemispheric connections in humans

Abstract

Visuospatial abilities arepreferentially mediatedbythe right hemisphere. Although this asymmetryoffunctionisthoughttobeduetoan unbalanced interaction between cerebral hemispheres, the underlying neurophysiological substrate isstill largely unknown. Here, using a methodof trifocal transcranial magnetic stimulation,weshow that the right, but not left, human posterior parietal cortex exertsastrong inhibitory activity over the contralateral homologous area byashort-latency connection. Wealso clarify, using diffusion-tensor magnetic resonance imaging, that such an interaction is mediated by direct transcallosal projections located in the posterior corpus callosum. We argue that this anatomo-functional network may represent a possible neurophysiological basis for the ongoing functional asymmetry between parietal cortices, and that its damage could contribute to the clinical manifestations of neglect. © 2011 the authors.