Developmental plasticity and memory.

The cerebral cortex of young kittens is known to be highly malleable during early postnatal development. However, most studies of developmental plasticity have been conducted in primary visual cortex. It has long been unclear to what extent similar plasticity exists in higher cortical areas. We have now studied developmental plasticity in the anterior ectosylvian (AE) region of the cat's parietal association cortex, which receives input from different sensory modalities. One area in this cortical region, which is predominantly visual in normal cats, area AEV, is taken over almost completely by auditory and somatosensory inputs, when cats are binocularly deprived of vision from birth. Furthermore, when single auditory neurons are tested with sound sources in free-field at different locations, they show sharper spatial tuning in visually deprived cats. This compensatory, crossmodal plasticity was explored at the behavioral level by testing visually deprived cats in an auditory localization task, and these cats could indeed localize sound sources more precisely than normal cats. These findings are interpreted as a form of adaptation of the young brain to an altered environment. Similar adaptation is still possible in adult brains by virtue of associative learning and long-term memory. It is argued that the synaptic mechanisms by which associative memories are stored in the cerebral cortex are similar to those in developmental plasticity, only the increment of learning is smaller in adult animals.