Short periods of darkness fail to restore visual or neural plasticity in adult cats.

It has been shown that the visual acuity loss experienced by the deprived eye of kittens following an early period of monocular deprivation (MD) can be alleviated rapidly following 10 days of complete darkness when imposed even as late as 14 weeks of age. To examine whether 10 days of darkness conferred benefits at any age, we measured the extent of recovery of the visual acuity of the deprived eye following the darkness imposed on adult cats that had received the same early period of MD as used in prior experiments conducted on kittens. Parallel studies conducted on different animals examined the extent to which darkness changed the magnitude of the MD-induced laminar differences of the cell soma size and immunoreactivity for the neurofilament (NF) protein in the dorsal lateral geniculate nucleus (dLGN). The results indicated that 10 days of darkness imposed at one year of age neither alleviated the acuity loss of the deprived eye induced by an earlier period of MD nor did it decrease the concurrent lamina differences of the soma size or NF loss in the dLGN.