Event-related TMS over the right posterior parietal cortex induces ipsilateral visuospatial interference

The right posterior parietal cortex (PPC) is implicated in visuo-spatial pr ocessing, as illustrated by patients with visuo-spatial neglect, but the pr ecise time-course of its contribution is still an open question. In the pre sent study we assessed whether single-pulse transcranial magnetic stimulati on (TMS) can interfere with the performance of normal subjects in a standar d visuo-spatial task. Participants had to perform a landmark task while TMS was applied over the right PPC, the homologue region in the left hemispher e or the right primary motor cortex. Stimulation was time-locked to the sti mulus presentation with a stimulus onset asynchrony (SOA) varying between 5 0 and 200 ms. Our results indicate that TMS interfered mainly with the visu o-spatial task when applied over the right PPC at an early stage (50 ms pos t-stimulus). The interference effect of single-pulse TMS in the present vis uo-spatial processing is revealed by a processing cost for ipsilateral targ ets. These results are in agreement with neuropsychological and brain imagi ng studies showing a right hemispheric dominance in visuo-spatial processin g but add crucial information about the time-course of visuo-spatial proces sing within the right PPC. NeuroReport 12:2369-2374 (C) 2001 Lippincott Wil liams & Wilkins.