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1 Institute of Cognitive Neuroscience & Dept of Psychology, University College London, London, United Kingdom
* To whom correspondence should be addressed. E-mail: juha.silvanto{at}ucl.ac.uk.
The precise role of frontal eye fields (FEF) in vision independent of their role in eye movements remains a matter of debate. One proposal is that the FEF exert top-down influences on the extrastriate visual cortex prior to eye movement preparation. Here we establish, using transcranial magnetic stimulation (TMS), that activity in the human frontal eye fields has a direct effect on the sensitivity of extrastriate visual area MT/V5, and that the spatial organisation of this top-down effect is lateralised in the human brain. We show that phosphene threshold (the TMS intensity required to elicit a visual perception) for MT/V5 stimulation changes as a function of the delay between the application of TMS over FEF and MT/V5. The effects were specific to the location and time of stimulation. Stimulation of FEF 20-40msecs prior to stimulation of MT/V5 decreased the intensity of MT/V5 stimulation required to elicit phosphenes: TMS of the right FEF changed the sensitivity of left and right MT whereas TMS of the left FEF changed the sensitivity only of the left MT/V5. Thus the sensitivity of human extrastriate cortex is modulated by activity in the FEF.
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