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Cerebral Cortex Advance Access originally published online on May 30, 2008
Cerebral Cortex 2009 19(2):327-330; doi:10.1093/cercor/bhn091
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© The Author 2008. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

The Perceptual and Functional Consequences of Parietal Top-Down Modulation on the Visual Cortex

Juha Silvanto1, Neil Muggleton, Nilli Lavie and Vincent Walsh

Institute of Cognitive Neuroscience and Department of Experimental Psychology, University College London, Alexandra House, 17 Queen Square, London, UK

Address correspondence to Juha Silvanto, PhD, Institute of Cognitive Neuroscience and Department of Experimental Psychology, University College London, Alexandra House, 17 Queen Square, London, UK. Email: jsilvant{at}bidmc.harvard.edu.

The posterior parietal cortex (PPC) has been proposed to play a critical role in exerting top-down influences on occipital visual areas. By inducing activity in the PPC (angular gyrus) using transcranial magnetic stimulation (TMS), and using the phosphene threshold as a measure of visual cortical excitability, we investigated the functional role of this region in modulating the activity of the visual cortex. When triple-pulses of TMS were applied over the PPC unilaterally, the intensity of stimulation required to elicit a phosphene from the visual cortex (area V1/V2) was reduced, indicating an increase in visual cortical excitability. The increased excitability that was observed with unilateral TMS was abolished when TMS was applied over the PPC bilaterally. Our results provide a demonstration of the top-down modulation exerted by the PPC on the visual cortex and show that these effects are subject to interhemispheric competition.

Key Words: phosphenes • posterior parietal cortex • top-down modulation • transcranial magnetic stimulation • V1/V2

1 Present address: Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School and Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA


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