The critical period for ocular dominance plasticity in the ferret's visualcortex

Microelectrode recordings and optical imaging of intrinsic signals were use d to define the critical period for susceptibility to monocular deprivation (MD) in the primary visual cortex of the ferret. Ferrets were monocularly deprived for 2, 7 or >14 d, beginning between postnatal day 19 (P19) and P1 10. The responses of visual cortical neurons to stimulation of the two eyes were used to gauge the onset, peak, and decline of the critical period. MD s ending before P32 produced little or no loss of response to the deprived eye. MDs of 7 d or more beginning around P42 produced the greatest effects. A rapid decline in cortical susceptibility to MD was observed after the se venth week of life, such that MDs beginning between P50 and P65 were approx imately half as effective as those beginning on P42; MDs beginning after P1 00 did not reduce the response to the deprived eye below that to the nondep rived eye. At all ages, 2 d deprivations were 55-85% as effective as 7 d of MD. Maps of intrinsic optical responses from the deprived eye were weaker and less well tuned for orientation than those from the nondeprived eye, wi th the weakest maps seen in the hemisphere ipsilateral to the deprived eye. Analysis of the effects of 7 d and longer deprivations revealed a second p eriod of plasticity in cortical responses in which MD induced an effect lik e that of strabismus. After P70, MD caused a marked loss of binocular respo nses with little or no overall loss of response to the deprived eye. The cr itical period measured here is compared to other features of development in ferret and cat.