Deficits in speed perception induced by transcranial magnetic stimulation of cortical area V5/MT+

Abstract

Single-unit neurophysiology in monkeys has highlighted a prominent role for cortical area V5/MT in the analysis of speed of moving objects. We wished to investigate whether human area V5/MT+ plays a similarly important role in speed perception by disrupting its function using transcranial magnetic stimulation (TMS) whilst observers performed speed discrimination behavioural tasks. Area V5/MT and other cortical areas responsive to motion were first localised in 5 subjects using functional magnetic resonance brain imaging (fMRI). Using neuronavigation techniques repetitive TMS (rTMS) was then applied unilaterally to these areas whilst observers performed a 2AFC delayed speed discrimination task with stimuli placed in the contra-lateral hemifield. When applied over V1, rTMS had no effect on speed discrimination performance. However, the application of rTMS to area V5/MT+ had two effects: firstly, it elevated speed discrimination thresholds and secondly, it induced a perceived slowing of the test stimulus. When observers performed a spatial frequency discrimination control task the application of rTMS to V5/MT+ did not affect observers? performance. These results indicate that disruption to human V5/MT+ generates selective deficits in the perception of stimulus speed and suggest that this area is likely to play an important role in this aspect of motion perception.