Single-unit response to AM sound in the auditory cortex.

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DESCRIPTION (provided by applicant): How does single neuron activity relate to perception? How do single neurons process temporally varying information, and how is this information encoded by their temporal firing pattern? The proposed study aims to address these fundamental questions. The auditory system is exceptional to study the union of these questions because of its unique design to analyze temporal structure in the acoustic environment. Amplitude-modulated (AM) sound provides temporal variation in sound intensity to which auditory neurons phase-lock. This straightforward relationship between temporal stimulus structure and temporal response properties provides an excellent framework to investigate temporal codes in the brain. We will record single-units responses in the primary auditory cortex (A1) and the middle-lateral field of the auditory cortex (ML) of non-human subjects while they actively discriminate AM. We will characterize temporal phase- locking of single neuron responses to AM with vector strength (VS). We will also measure spike-counts in response to AM. With analytical techniques derived from signal detection theory, we will determine behavioral AM sensitivity and neural AM sensitivity based on both VS and spike-count. By simultaneously recording behavior and neural activity and comparing them with analogous statistical measures, the design of this study allows us to directly link neural activity to behavior. Here, we aim to address three specific questions; 1) whether, temporal or rate codes, can better account for AM discrimination ability; 2) whether active engagement in AM discrimination improves the temporal precision of neural firing as well as rate coding of AM in A1 and ML; 3) whether some neurons' activities in A1 and ML are closely associated with the animal's decisions. Comparative study of A1 and ML will add to the understanding of parallel and hierarchical processing of temporal sound properties in the auditory cortex and how this processing is modulated by behavioral state. In addition, the study will take the first step to understand the degree of synchrony of activity across nearby neurons, which is critical to derive models of how neural sensitivity can be accounted for by a population of neurons. This study will add to the understanding of how speech is processed, as speech is rich with AM. This will also add to the understanding of temporal processing which has been linked to several learning impairments. Additionally, cochlear implants transmit amplitude and temporal information of sound as principal cues, and the understanding of how temporal information is processed upstream in auditory system should help in the design of these prostheses to improve the hearing of the impaired.