Based on results from other species, especially cats and mice, the cochlear nuclear (CN) complex plays a critical role in the ensemble temporal coding of auditory information. Auditory nerve (AN) fibers project tonotopically to several sub-regions of the CN, which give rise to different parallel ascending pathways. Projection cells of the CN complex make contact with other nuclei of the auditory brainstem, as well as direct contact with cells in the inferior colliculus (IC). As a first obligatory intermediary between the AN and the ascending auditory pathway, the CN is in a unique position to determine the basic auditory code. Because the CN complex plays a fundamental role in encoding auditory information, and because big brown bats have an especially time-based representation of auditory space and objects, we are interested in the temporal response of the CN to echolocation-relevant acoustic stimuli.

To explore the first-stage encoding of acoustic objects, we use in vivo electrophysiology and free-field acoustic stimulation. Field potential and unit activity are recorded in response to signals that mimic natural echolocation sounds as well as tones and non-natural FM sounds. In addition to temporal response properties such as latency and latency deviation, we are interested in the relationship between unit and field activity in this early auditory center.