Early extrastriate activity without primary visual cortex in humans (original) (raw)

2000, Neuroscience Letters

Damage to the primary visual cortex (V1) destroys the major source of anatomical input to extrastriate cortical areas (V2, V3, V4 and V5) and produces cortical blindness ± an absence of any sensation of light and colour ± in the visual ®eld contralateral to the side of the lesion. Neuroimaging studies, nevertheless, have recently demonstrated dorsal and ventral extrastriate activation for stationary stimuli presented to the blind visual ®eld in the absence of V1 activity in human subjects. To clarify the moment in time that visual information reaches extrastriate areas, by means of eventrelated potentials (ERPs) we tracked the temporal course of responses to complex visual stimuli (faces) presented in the blind ®eld of a hemianopic patient. Stimulation of the normal visual ®eld elicited a positive occipital de¯ection (P1) at 140 ms. A P1 response was also observed with stimulation of the blind ®eld, although slightly delayed (20 ms) and reduced. Its topography and timing demonstrate that early neural activity for stationary stimuli takes place within extrastriate regions despite V1 denervation. q

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