Manifestation of scotomas created by transcranial magnetic stimulation of human visual cortex

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Abstract
Reduced visual performance under transcranial magnetic stimulation (TMS) of human visual cortex demonstrates suppression whose spatial extent is not directly visible. We created an artificial scotoma (region missing from a visual pattern) to directly visualize the location, size and shape of the TMS-induced suppression by following a large-field, patterned, visual stimulus with a magnetic pulse. The scotoma shifted with coil position according to known topography of visual cortex. Visual suppression resulted in pattern-dependent distortion, and the scotoma was filled in with temporally adjacent stimuli, suggesting spatial and temporal completion mechanisms. Thus, perceptual measurements of TMS-induced suppression may provide information about cortical processing via neuronal connections and temporal interactions of neural signals.