Development of temporal response properties and contrast sensitivity of V1 and V2 neurons in macaque monkeys.

The temporal contrast sensitivity of human infants is reduced compared to that of adults. It is not known which neural structures of our visual brain sets limits on the early maturation of temporal vision. In this study we investigated how individual neurons in the primary visual cortex (V1) and visual area 2 (V2) of infant monkeys respond to temporal modulation of spatially optimized grating stimuli and a range of stimulus contrasts. As early as 2 wk of age, V1 and V2 neurons exhibited band-pass temporal frequency tuning. However, the optimal temporal frequency and temporal resolution of V1 neurons were much lower in 2- and 4-wk-old infants than in 8-wk-old infants or adults. V2 neurons of 8-wk-old monkeys had significantly lower optimal temporal frequencies and resolutions than those of adults. Onset latency was longer in V1 at 2 and 4 wk of age and was slower in V2 even at 8 wk of age than in adults. Contrast threshold of V1 and V2 neurons was substantially higher in 2- and 4-wk-old infants but became adultlike by 8 wk of age. For the first 4 wk of life, responses to high-contrast stimuli saturated more readily in V2. The present results suggest that although the early development of temporal vision and contrast sensitivity may largely depend on the functional maturation of precortical structures, it is also likely to be limited by immaturities that are unique to V1 and V2.