Azimuthal representation within a population of interaural intensity‐sensitive neurons

Abstract

One‐third of the central nucleus of the inferior colliculus (ICC) in the mustache bat is devoted to processing information at 60 kHz, a dominant component of the echolocation pulse. Within this 60‐kHz region, E‐I type neurons sensitive to interaural intensity disparities (IIDs) are grouped together. Their IID sensitivity changes in orderly fashion along the vertical axis of the ICC. Dorsal‐most neurons require the highest relative inhibitory intensity to suppress activity, the most ventral require the lowest. Regardless of their IID sensitivity, all neurons had lowest excitatory thresholds for the same azimuthal sound location. IID sensitivity did, however, influence their overall responsiveness to azimuthal locations across the frontal sound field. E‐I neurons with the highest inhibitory thresholds responded to sounds throughout the frontal field. As inhibitory thresholds dropped, their medial receptive field borders shifted systematically across the azimuth toward the area of lowest excitatory thresholds. The percentage of excited neurons within this population will therefore shift systematically along the vertical axis of the ICC as a function of azimuthal location. [Work supported by NIH, NSF.]