The proposed work investigates the representation of information about sound in the central nucleus of the inferior colliculus (CNIC). This structure receives a complex array of inputs containing different kinds of information about the sounds coming into the ears. As many as 20-30 separate processing centers in the brainstem contribute inputs to the CNIC. These include information about what the sound is, who or what produced it, and where the source is located. All of this information must pass through the CNIC on the way to the cortex, so the way in which the neurons of the CNIC assemble these diverse representations is essential to understanding auditory processing. Three investigations are proposed. First, a new statistical method will be applied to construct generic models of the receptive fields of neurons in CNIC. These models will allow understanding of the way the identity of sounds and their information content is represented. Second, the way in which the three cues for sound localization are combined in neurons of the CNIC will be studied. This will provide insights into the way in which neurons encode multiple aspects of stimuli, a common problem in all parts of the brain. Third, the circuits that amplify dynamic features of sound will be studied. These elements allow us to deal with complex acoustic environments with multiple sound sources, especially with the problem of separating sources that produce overlapping sounds.
The research proposed here is aimed at understanding the processing of complex signals in the brain. The work will focus on the central nucleus of the inferior colliculus (CNIC), which is relevant to two important ongoing developments in auditory prostheses. First, a major outstanding problem in auditory prostheses is the inability of users to parse complex auditory scenes, e.g. to pick out one sound source among many using current devices. The neurons of the CNIC seem to be involved in computations important to scene parsing. For example, they respond strongly to changes in a sound or to new elements of a sound and they construct the sense of sound source localization. It is important to understand these computations in normal and impaired auditory systems to help design ways to maintain their function in prostheses. Second, the CNIC is now the target location for one type of central prosthetic implant (the auditory midbrain implant) and it is important to know how to encode information to best present it to CNIC neurons electrically.
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