Seasonal plasticity in the adult brain

Seasonal plasticity of structure and function is a fundamental feature of n ervous systems in a wide variety of animals that occupy seasonal environmen ts. Excellent examples of seasonal brain changes are found in the avian son g control system, which has become a leading model of morphological and fun ctional plasticity in the adult CNS. The volumes of entire brain regions th at control song increase dramatically in anticipation of the breeding seaso n. These volumetric changes are induced primarily by vernal increases in ci rculating sex steroids and are accompanied by increases in neuronal size, n umber and spacing. In several species, these structural changes in the song control circuitry are associated with seasonal changes in song production and learning. Songbirds provide important insights into the mechanisms and behavioral consequences of plasticity in the adult brain.