Responses of neurons in neonatal cortex and thalamus to patterned visual stimulation through the naturally closed lids.

In studies of the developing mammalian visual system, it has been axiomatic that visual experience begins with eye-opening. Any role for neuronal acti vity earlier in development has been attributed to the patterned spontaneou s activity found in retina and lateral geniculate nucleus (LGN). Here we sh ow that, as early as 2 wk before eye-opening, visual stimuli presented thro ugh the closed eyelids can drive neuronal activity in LGN and striate corte x of the ferret. At this age, spontaneous activity in cortex is much lower than in LGN, and the visual responses of many cortical, but not geniculate, neurons depend on the orientation of a moving grating. Furthermore the sel ectivity of cortical neurons to the orientation of gratings presented throu gh the closed eyelids improves with age. Thus neuronal activity patterned b y visual experience, rather than by spontaneous retinal activity, is presen t in visual cortex much earlier than previously thought. This could have im portant implications for the self-organization of visual cortex.