Visual cortical plasticity in infant kittens.

The visual cortex of the cat is characterized by marked modifiability of neuronal responsiveness by visual experience in infancy, and stereotyped pattern of functional architectures in adulthood. The question of how the plasticity of the infant visual cortex is compatible with the regular patterns of the adult visual cortex has been a central problem of the brain neuroscience. This question was answered by quantifying the plasticity in the visual cortical circuitry of the infant kittens as changes in synaptic transmission produced after conditioning stimulation of the visual pathway. The results indicate that the solution of this question is the heterogeneous distribution of the synaptic plasticity in the infant visual cortex: the plasticity is not uniformly present in the visual cortical circuitry, but is limited only to a part of the circuitry (the cortico-cortical synapses in the supragranular layers). Therefore, the visual function (photic responsiveness) may be learned during the postnatal life of the kittens by the supragranular cells with plastic synapses, while the other cortical cells with fewer plastic synapses put prenatally designed constraints on the learning, so that the learning yields the adult cortical circuitry with regular patterns of organization.