A role of afferent activity in the maturation of thalamocortical connections of visual system

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Binocular visual responsiveness of neurons in visual cortex of cats, monkeys and other mammals including humans can be changed by monocular visual deprivation in the critical period of postnatal development, one of the best-known examples of experience-dependent modification of brain function.It is hypothesized that afferents from each eye compete with one another for synaptic connections with cortical neurons so that less active afferents from the deprived eye fail to maintain the connections, i.e., balance between activities of both afferents is important to determine the fate of each eye-specific pathway.This synaptic competition hypothesis has been supported by various types of deprivation experiments in kittens. If such a competition hypothesis is valid, then an increase in inputs from one eye instead of decrease due to deprivation should also change binocular responsiveness of cortical neurons. Otherwise the deprivation-induced change might be due to "disuse" weakening of responsiveness.However, the hypothesis has never been tested with such a monocular activation paradigm. In the present project, we activated one of the optic nerves by electrical stimulation in behaving kittens for 2 days, and found that such a chronic, monocular activation induced a shift in ocular dominance of visual responses of cortical neurons.