This revised renewal application carries on the study of how auditory space is encoded in the barn owl's brain. The owl's specialization for capturing prey using auditory cues provides distinct advantages towards elucidating the emergence of tuning properties and the neural code underlying sound localization. Spatial cues are strongly frequency dependent. Additionally, location must be encoded in parallel with spectrotemporal features which are used to infer the sound's identity. This means that the natural auditory scene is multidimensional in its essence. This proposal approaches the coding of auditory space in this compound context.
Aim 1 investigates the relationship between frequency and spatial tuning. We have found correlation between the tuning of frequency and tuning to the spatial cue for the horizontal axis, interaural time difference (ITD), in the map of auditory space of owl's midbrain. Correlation between frequency and ITD tuning has also been observed in the brainstem and midbrain of mammals, which provides an avenue for establishing links across species.
This aim will investigate where the correlation emerges and how it influences the response of midbrain tegmentum neurons, which readout the midbrain map to command orienting behavior.
Aim 2 examines the integrated coding of sound direction and identity. Precision in coding sound identity will be approached by examining the reproducibility of responses across sound repetitions. Our recent studies suggest that reproducibility depends on sound direction and is enhanced in the processing pathway that conveys information about interaural level difference (ILD). We will test these hypotheses in space-specific neurons of the owl's midbrain usingin vivo extracellular and intracellular recordings and sound stimulation in free field.
Aim 3 investigates the coding underlying the owl's head-orienting responses, taking into account the dependency between frequency and ITD tuning and the location-dependent selectivity for sound identity examined in aims 1 and 2 with modeling. The model will be guided by the hypothesis that a rate-code for sound localization emerges by convergence from the map of auditory space onto midbrain tegmentum neurons. This code is consistent with the rate code proposed for mammals. The model's predictions will be tested using in vivo recordings in the midbrain and behavior. This research will advance knowledge of how cues for sound location and sound identity are integrated in the midbrain and provide a unifying theory linking the neural coding of ITD across species. Understanding cue integration in central auditory processing will lead to more accurate interpretations of auditory perception and hearing disorders, allowing for the design of more efficient treatments.
The proposed research investigates the coding and neural processing underlying the ability to localize sound. The question will be addressed in the sound localization system of the owl. The owl's specialization offers distinct advantages for connecting behavior with the underlying neural computations and coding. The project approaches sound localization in the context of a multidimensional auditory scene, where the sound's pitch and identity are taken into account.It also establishes links between the neural code used in avian and mammalian brains. The approach is multidisciplinary, combining extracellular and intracellular in vivo electrophysiology, microstimulation, and behavior. This research can lead to seminal understanding of how the brain across species represents sound direction in natural auditory scenes
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