Sound Localization by the Pallid Bat, Antrozous pallidus
While the auditory cortex is necessary for sound localization, we do not yet know the underlying mechanisms that lead to the behavior. To address this gap, we have designed and executed a series of experiments aimed at describing the neuroethology of sound localization in the pallid bat, an animal which relies on passive hearing of prey-generated noise when foraging. We have made three primary discoveries. First, we have discovered how the external ear filters incoming sounds before they reach the sensory epithelium. Low frequency spectral notches, important for the perception of sound source elevation, depend on the presence of the conspicuous tragus. Second, we developed a sound localization task to test the behavior of the pallid bat. Pallid bats demonstrate remarkable sound localization acuity of ~4° near the midline, and we show that the high frequency range of prey-generated noise (20-30 kHz) is the predominant bandwidth used for azimuth localization. Last, we describe the 2D spatial selectivity of auditory cortex neurons and propose a population code for 2D sound localization. Our data suggests that the extent of active cortex is constrained systematically by the horizontal and elevational sound source direction. We describe preliminary results that indicate the chemogenetic inhibitory DREADDs system is a viable method for answering questions about the necessity of these auditory cortex populations to sound localization behavior. Collectively, the research contained in this dissertation provides insight into the way the auditory system is able to compute representations of external space from sound filtered by the external ear and supports the notion of the pallid bat as a viable model from which basic understandings of mammalian sound localization can be obtained.