Early auditory experience induces frequency-specific, adaptive plasticity in the forebrain gaze fields of the barn owl

Binaural acoustic cues such as interaural time and level differences (ITDs and ILDs) are used by many species to determine the locations of sound sour ces. The relationship between cue values and locations in space is frequenc y dependent and varies from individual to individual. In the current study, we tested the capacity of neurons in the forebrain localization pathway of the barn owl to adjust their tuning for binaural cues in a frequency-depen dent manner in response to auditory experience. Auditory experience was alt ered by raising young owls with a passive acoustic filtering device that ca used frequency-dependent changes in ITD and ILD. Extracellular recordings w ere made in normal and device-reared owls to characterize frequency-specifi c ITD and ILD tuning in the auditory archistriatum (AAr), an output structu re of the forebrain localization pathway. In device-reared owls, individual sites in the AAr exhibited highly abnormal, frequency-dependent variations in ITD tuning, and across the population of sampled sites, there were freq uency-dependent shifts in the representation of ITD. These changes were in a direction that compensated for the acoustic effects of the device on ITD and therefore tended to restore a normal representation of auditory space. Although ILD tuning was degraded relative to normal at many sites in the AA r of device-reared owls, the representation of frequency-specific ILDs acro ss the population of sampled sites was shifted in the adaptive direction. T hese results demonstrate that early auditory experience shapes the represen tation of binaural cues in the forebrain localization pathway in an adaptiv e, frequency-dependent manner.