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

Reduced visual performance under transcranial magnetic stimulation (TMS) of human visual cortex demonstrates suppression whose spatial extent is not d irectly visible. We created an artificial scotoma (region missing from a vi sual 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 adjacen t stimuli, suggesting spatial and temporal completion mechanisms. Thus, per ceptual measurements of TMS-induced suppression may provide information abo ut cortical processing via neuronal connections and temporal interactions o f neural signals.