Visually Evoked Slow Negativity in Rabbit Cortex.

Abstract

Visual cortex responses to optic nerve and retinal stimulation were studied by D.C. recording upon slow time line. A prominent slow negative wave (250 to 400 msec. duration), slow negativity, occurred in the wake of primary visual response. Evidence indicates that when activated by nerve stimulation it has a threshold somewhat lower than that of primary response. Under moderately deep Nembutal anesthesia, slow negativity (evoked by optic nerve or light flash stimuli) disappears and is replaced by a longer lasting positive after-effect. The slow negativity described under these conditions is believed to have an origin in the cortex identical with corresponding slow negative waves evoked by direct surface and midline thalamic stimulation. In Fig. 3 it is placed schematically with relation to other components of visual cortical response previously described elsewhere.