Axonal Delay Lines for Time Measurement in the Owl's Brainstem

Interaural time difference is an important cue for sound localization. In the barn owl (Tyto alba) neuronal sensitivity to this disparity originates in the brainstem nucleus laminaris. Afferents from the ipsilateral and contralateral magnocellular cochlear nuclei enter the nucleus laminaris through its dorsal and ventral surfaces, respectively, and interdigitate in the nucleus. Intracellular recordings from these afferents show orderly changes in conduction delay with depth in the nucleus. These changes are comparable to the range of interaural time differences available to the owl. Thus, these afferent axons act as delay lines and provide anatomical and physiological bases for a neuronal map of interaural time differences in the nucleus laminaris