Mechanisms of experience-dependent plasticity in the auditory localizationpathway of the barn owl

Sound localization is a computational process that requires the central ner vous system to measure various auditory cues and then associate particular cue values with appropriate locations in space. Behavioral experiments show that barn owls learn to associate values of cues with locations in space b ased on experience. The capacity for experience-driven changes in sound loc alization behavior is particularly great during a sensitive period that las ts until the approach of adulthood. Neurophysiological techniques have been used to determine underlying sites of plasticity in the auditory space-pro cessing pathway. The external nucleus of the inferior colliculus (ICX), whe re a map of auditory space is synthesized, is a major site of plasticity. E xperience during the sensitive period can cause large-scale, adaptive chang es in the tuning of ICX neurons for sound localization cues. Large-scale ph ysiological changes are accompanied by anatomical remodeling of afferent ax ons to the ICX. Changes in the tuning of ICX neurons for cue values involve two stages: (I) the instructed acquisition of neuronal responses to novel cue values and (2) the elimination of responses to inappropriate cue values . Newly acquired neuronal responses depend differentially on NMDA receptor currents for their expression. A model is presented that can account for th is adaptive plasticity in terms of plausible cellular mechanisms.