FUNCTIONAL ORGANIZATION--NONPRIMARY AUDITORY CORTEX

Georgetown University, Washington DC

Investigators

Linked publications & trials

Abstract

DESCRIPTION: Multiple cortical maps and their functional specialization have been demonstrated extensively in the visual system of primates. Much less is known about multiple representations in the auditory cortex. This is surprising because a thorough knowledge of nonprimary auditory cortex is undoubtedly necessary for the ultimate understanding of the neural basis of speech perception and of a variety of central speech and hearing disorders. The goal of my research is to identify the role different areas in the auditory cortex of the rhesus monkey play in auditory perception, in auditory scene analysis, and in the neural decoding of complex sounds, particularly those relevant for acoustic communication. Analogies to feature extraction and figure-ground discrimination in the visual system will be drawn as closely as possible. Neurons in higher cortical areas are known to be selective for more complex stimuli. The first specific aim of this proposal is, therefore, to analyze, using complex sounds, the nature of stimulus preferences in single neurons of non primary auditory cortex in the rhesus monkey and the mechanisms for generating these preferences (Hypothesis 1: Neurons in non primary auditory cortex respond to progressively more complex sounds within a hierarchy of cortical areas). The use of behaviorally relevant, species-specific vocalizations and their component elements will receive particular attention for the analysis of single neurons in the superior temporal gyrus (STG). The response will be compared to those in primary auditory cortex. The second aim is then to investigate the organization of stimulus preferences into computational maps across the cortical surface in the STG, particularly the lateral belt areas (Hypothesis 2: Stimulus preferences within a certain parameter domain is organized in an orderly fashion parallel to the cortical surface). Thirdly, the connections between different cortical areas and their input from the thalamus will be identified using anatomical tracers injected into physiologically identified regions (Hypothesis 3: regions with similar stimulus preferences are connected to regions with the same preference, whereby a convergence from wider input regions takes place in hierarchically higher areas). The laminar organization of input/output connections in the cortex will receive particular attention through careful track reconstructions. This research will advance our understanding of the functional organization and specialization of the cerebral cortex in higher mammals and its role in sensory perception. In particular, it will aid our understanding of non primary auditory cortex and of the neural mechanisms underlying the processing of complex sounds. It will rejuvenate work on the neurobiology of acoustic communication in primates and thus provide an important link between the neuroethological work in more specialized species and functional brain imaging work in humans on auditory speech perception. Ultimately, it will aid the understanding of major dysfunctions of hearing, such as sensory and phonological aphasia and will enable us to design more appropriate auditory prostheses based upon processing principles in the central auditory system.