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The Journal of Neuroscience, July 2, 2008, 28(27):6848-6857; doi:10.1523/JNEUROSCI.1287-08.2008

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Behavioral/Systems/Cognitive
Induced Deficits in Speed Perception by Transcranial Magnetic Stimulation of Human Cortical Areas V5/MT+ and V3A

Declan J. McKeefry,¹ Mark P. Burton,¹ Chara Vakrou,¹ Brendan T. Barrett,¹ and Anthony B. Morland²

¹School of Optometry and Vision Science, University of Bradford, Bradford, West Yorkshire BD7 1DP, United Kingdom, and ²York Neuroimaging Centre, Department of Psychology, University of York, York YO10 5DD, United Kingdom

Correspondence should be addressed to Declan J. McKeefry, School of Optometry and Vision Science, School of Life Sciences, University of Bradford, Bradford, West Yorkshire BD7 1DP, UK. Email: d.mckeefry{at}bradford.ac.uk

In this report, we evaluate the role of visual areas responsive to motion in the human brain in the perception of stimulus speed. We first identified and localized V1, V3A, and V5/MT+ in individual participants on the basis of blood oxygenation level-dependent responses obtained in retinotopic mapping experiments and responses to moving gratings. Repetitive transcranial magnetic stimulation (rTMS) was then used to disrupt the normal functioning of the previously localized visual areas in each participant. During the rTMS application, participants were required to perform delayed discrimination of the speed of drifting or spatial frequency of static gratings. The application of rTMS to areas V5/MT and V3A induced a subjective slowing of visual stimuli and (often) caused increases in speed discrimination thresholds. Deficits in spatial frequency discrimination were not observed for applications of rTMS to V3A or V5/MT+. The induced deficits in speed perception were also specific to the cortical site of TMS delivery. The application of TMS to regions of the cortex adjacent to V5/MT and V3A, as well as to area V1, produced no deficits in speed perception. These results suggest that, in addition to area V5/MT+, V3A plays an important role in a cortical network that underpins the perception of stimulus speed in the human brain.

Key words: transcranial magnetic stimulation; fMRI; retinotopic mapping; psychophysics; speed perception; V5/MT+; V3A

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Received May 1, 2008; revised May 1, 2008; accepted May 21, 2008.

Correspondence should be addressed to Declan J. McKeefry, School of Optometry and Vision Science, School of Life Sciences, University of Bradford, Bradford, West Yorkshire BD7 1DP, UK. Email: d.mckeefry{at}bradford.ac.uk

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