Chronic electrical stimulation of afferents from one eye changes ocular dominance of visual cortical neurons in...

Binocular visual responsiveness of neurons in visual cortex of the cat can be changed by monocular visual deprivation in the critical period of postnatal development. 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. This hypothesis predicts that an increase in inputs from one eye instead of decrease due to deprivation should also change binocular responsiveness of cortical neurons. However, the hypothesis has not successfully been tested with experimental activation of afferents from one eye. In the present study, we activated one of the optic nerves by chronic electrical stimulation of theta-burst type in behaving kittens for 2 days. After such a monocular activation, visual cortical neurons showed a significant ocular dominance shift in favor of the electrically activated eye, although neurons in the activated and nonactivated layers of the dorsal lateral geniculate nucleus had no biased visual responses. Also, we found no detectable difference between activated and nonactivated eye responses of cortical neurons in other response properties such as orientation selectivity. These results support the hypothesis that the balance between activities of both afferents is critical for formation or consolidation of each eye-specific pathway.