Early development of direction selectivity in higher visual cortex.

A fundamental aspect of visual motion processing is the computation of motion direction. In ferrets, as in primates, selectivity for motion direction is found both in early cortical stages like the primary visual cortex (V1) and in higher visual areas like primate MT and ferret PMLS. Little is known about how this critical tuning function develops in higher visual cortex. Here, by studying the development of the ferret's motion pathway, we first reveal the surprising finding that direction selectivity develops earlier in PMLS than in V1, contrary to the areas' hierarchical positions. Our data furthermore show that while direction selectivity is sensitive to visual experience in both areas, the sensitivity profile differs between them: Moving stimuli, containing both spatial and temporal cues, are required to promote direction selectivity development in V1, but flashing stimuli that remain stationary spatially are sufficient for direction selectivity development in PMLS. Collectively, our findings reveal that the development of the motion pathway is highly complex when considered at the network level, and does not adhere to a simple feedforward model in which the development of lower visual areas sets the pace for higher ones. Not only will developmental models need to be updated to include this complexity, characterizing the link between the development of different visual areas will likely also be crucial for understanding the consequences of developmental disorders.