Binaural Neural Processing in the Auditory Midbrain

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Hearing is dependent on the brain. Our long-term goal is to determine how sounds from an environment are represented in electrical signals generated in the brain and how the representation is dependent on neural circuits, neurochemicals, and neurophysiological processes. Our short-term goal for the next five years is to investigate how a key hearing-related brain structure named the inferior colliculus integrates information obtained at the two ears. A sound from an natural environment can impinge on the left and right ears and generate two stimuli at the ears, respectively. The strengths and timing of the two stimuli are dependent on the location of the sound. Stimulation of the two ears leads to two sets of signals in the left and right auditory neural pathways. These signals are integrated by neurons in the inferior colliculus and other auditory processing centres, so that characteristics of the sound including its spatial location can be gauged by the brain. When multiple sounds exist in an environment, each sound can elicit signals in the auditory neural pathways. Integration of signals elicited by different sounds makes the response to one sound depend on the other, which can greatly affect the perception of each sound. In our research, we will find how a preceding sound generates an aftereffect to shape the response of a neuron to a subsequent sound. We will determine how such an aftereffect is dependent on the spatial relationship between the sounds. We will discover how this dependence is generated as a result of integration of neural signals from the left and right pathways. The rat will be used as an animal model, as it has a keen sense of hearing. Abundant basic knowledge has been obtained about its auditory system. The rat shares basic auditory neural mechanisms with many other mammals. Further research using the rat can enable us to fully understand hearing mechanisms in this species, which will greatly benefit the comprehension of hearing mechanisms in mammals in general. We choose to focus on the inferior colliculus as existing evidence indicates that neurons in this structure are important for the processing of information related to sound quality, timing, and location. Results from our research will help us understand neural mechanisms underlying important aspects of hearing such as localization of sounds and segregation of individual sounds. Comparing our results with existing literature will allow us to identify hearing mechanisms shared by different mammalian species. Thus, this research will significantly advance the field of auditory neuroscience. Knowledge generated from this study about neural processing of temporal changes of spatial acoustic cues can be applied in the future by engineers to develop intelligent hearing-enhancing devices. In addition to generating basic scientific knowledge, this research will provide essential training to students to help them become future leaders in neuroscience research.