SENSITIVE PERIODS FOR VISUAL CALIBRATION OF THE AUDITORY SPACE MAP INTHE BARN OWL OPTIC TECTUM

Previous studies have identified sensitive periods far the developing barn owl during which visual experience has a powerful influence on th e calibration of sound localization behavior. Here we investigated neu ral correlates of these sensitive periods by assessing developmental c hanges in the capacity of visual experience to alter the map of audito ry space in the optic tectum of the barn owl. We used two manipulation s. (1) We equipped owls with prismatic spectacles that optically displ aced the visual field by 23 degrees to the left or right, and (2) we r estored normal vision to prism-reared owls that had been raised wearin g prisms. In agreement with previous behavioral experiments, we found that the capacity of abnormal visual experience to shift the tectal au ditory space map was restricted to an early sensitive period. However, this period extended until later in life (similar to 200 d) than desc ribed previously in behavioral studies (similar to 70 d). Furthermore, unlike the previous behavioral studies that found that the capacity t o recover normal sound localization after restoration of normal vision was lost at similar to 200 d of age, we found that the capacity to re cover a normal auditory space map was never lost. Finally, we were abl e to reconcile the behaviorally and neurophysiologically defined sensi tive periods by taking into account differences in the richness of the environment in the two sets of experiments. We repeated the behaviora l experiments and found that when owls were housed in a rich environme nt, the capacity to adjust sound localization away from normal extende d to later in life, whereas the capacity to recover to normal was neve r lost. Conversely, when owls were housed in an impoverished environme nt, the capacity to recover a normal auditory space map was restricted to a period ending at similar to 200 d of age. The results demonstrat e that the timing and even the existence of sensitive periods for plas ticity of a neural circuit and associated behavior can depend on multi ple factors, including (1) the nature of the adjustment demanded of th e system and (2) the richness of the sensory and social environment in which the plasticity is studied.