Inter-hemispheric competition during postnatal development.

Functional asymmetries between the two sides of the brain, a well documented phenomenon in species as different as frog and man, are thought to arise from genetically determined anatomical differences which, at least in humans, may be observed in utero. Functional asymmetries can, however, be reversed after damage to one side of the brain. Here we report that rearing of kittens with the optic chiasm sectioned and one eyelid sutured during postnatal development results in a functional asymmetry in the corpus callosum, a bidirectional pathway which inter-connects the visual cortices on the two sides of the brain. Visual input originating on the side of the brain ipsilateral to the sutured eye loses the ability to influence cells on the other side of the brain. Conversely, visual input originating on the side of the brain ipsilateral to the exposed eye markedly increases its influence in the other hemisphere.