The functional organization of the pallid bat auditory cortex

The pallid bat listens passively to low-frequency, prey-generated noise to localize prey, while reserving high-frequency echolocation for general orientation and obstacle avoidance. This dissertation addresses how the auditory cortex of the pallid bat is organized to process information arising from echolocation and passive hearing. Particular emphasis is placed on determining the mechanisms involved in identifying the locations of sound sources and how the cortex is organized to deal with multiple sounds arriving within short time intervals.; The pallid bat auditory cortex appears to be organized to process information about two behaviorally-relevant sounds in segregated pathways. Each pathway contains an independent representation of sound locations. Within the cortical region that prefers low-frequency noise, a great majority of neurons are binaurally inhibited. Within this large cluster of binaurally inhibited neurons a systematic organization of interaural intensity difference sensitivity is present. This systematic organization of binaural sensitivity may underlie a population code for topographic representation of sound locations that may serve prey-localization. The afferent projections from the ventral division of the medial geniculate body in the thalamus to the map of binaural sensitivity is also systematic, with different rostrocaudal thalamic loci projecting to neurons with different binaural sensitivity. This suggests that a systematic map of binaural sensitivity is already present in the thalamus. Responses of neurons to low-frequency noise and echolocation sounds presented within short time intervals suggests that additional physiological mechanisms are in place to enhance functional segregation of pathways even when the two sounds arrive within short time intervals.