Shared features of the auditory system of birds and mammals

Although birds and mammals diverged about 300 Mya, their cochlear nuclei share similar features, including heterogeneous cell populations, and similar responses to sound. These shared characteristics may represent similar responses to selective pressures to encode the features of airborne sound. The cochlear nuclei of both birds and mammals share similar rules of cellular organization, although there appear to be no direct correspondences between neurons in each clade. Instead, shared features may be used to identify common computational strategies. In both birds and mammals, the cochlear nuclei encode parallel ascending streams of auditory information. One stream conveys precise temporal information from the two ears to a second-order nucleus that computes interaural time differences (ITDs). In both birds and mammals, these second-order neurons act as coincidence detectors and encode ITD. Despite this key similarity, there appear to be fundamental differences in the representation of auditory space in birds and mammals, indicating the parallel evolution of spatial hearing.