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Cerebral Cortex Advance Access published online on May 22, 2009
Cerebral Cortex, doi:10.1093/cercor/bhp102
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

The Cortical Site of Visual Suppression by Transcranial Magnetic Stimulation

A. Thielscher1, A. Reichenbach1, K. Ugurbil2 and K. Uludag1

1 High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, 72076 Tübingen, Germany, 2 Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA

Address correspondence to Dr Axel Thielscher, Max Planck Institute for Biological Cybernetics, Spemannstraße 41, D-72076 Tübingen, Germany. Email: axel.thielscher{at}tuebingen.mpg.de.

In visual suppression paradigms, transcranial magnetic stimulation (TMS) applied ~90 ms after visual stimulus presentation over occipital visual areas can robustly interfere with visual perception, thereby most likely affecting feedback activity from higher areas (Amassian VE, Cracco RQ, Maccabee PJ, Cracco JB, Rudell A, Eberle L. 1989. Suppression of visual perception by magnetic coil stimulation of human occipital cortex. Electroencephalogr Clin Neurophysiol 74:458–462.). It is speculated that the observed effects might stem primarily from the disruption of V1 activity. This hypothesis, although under debate, argues in favor of a special role of V1 in visual awareness. In this study, we combine TMS, functional magnetic resonance imaging, and calculation of the induced electric field to study the neural correlates of visual suppression. For parafoveal visual stimulation in the lower right half of the visual field, area V2d is shown to be the likely TMS target based on its anatomical location close to the skull surface. Furthermore, isolated stimulation of area V3 also results in robust visual suppression. Notably, V3 stimulation does not directly affect the feedback from higher visual areas that is relayed mainly via V2 to V1. These findings support the view that intact activity patterns in several early visual areas (rather than merely in V1) are likewise important for the perception of the stimulus.

Key Words: area V2 • primary visual cortex • transcranial magnetic stimulation • visual awareness • visual suppression


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