Structural and Functional Measures of Auditory Cortical Development

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The normal development of auditory cortex begins with a rough blueprint of pathways laid down prior to hearing onset, and is followed by a period of refinement that depends upon sound-evoked neural activity. These processes are guided by windows of time during which the brain is maximally adaptable, referred to as sensitive periods for normal development. The temporal dynamics of these periods are crucial to sensory development; however a thorough investigation relating structural and functional changes to auditory cortex has not been undertaken in the cat, despite decades of relying upon this model for the study of normal and abnormal perception. Instead, principles of neural plasticity observed in the visual cortex are broadly applied to all developing cortical areas with little consideration for significant anatomical and functional differences between brain regions. Thus, the long-term goal of this research program is to combine classical neuroanatomical techniques with cutting-edge high-field functional imaging methodologies to develop a detailed understanding of auditory cortical development. We propose to combine immunohistochemical markers of neuronal development and retrograde tracers with advanced, structural and functional magnetic resonance imaging (MRI) to examine auditory cortical development in the cat. Moreover, we will manipulate sound-evoked activity onset to define temporal boundaries of sensitive periods for normal development of structure and function. We will elucidate patterns of laminar development, monitor changes in connectivity between sensory cortices, and establish developmental timelines for the onset of cortical function throughout the hierarchy of processing. We hypothesize these methods will reveal a timeline for structural and functional maturity that begins in core auditory cortex (A1 and AAF), and proceeds toward higher-level fields, and which is perturbed by delayed hearing onset, leading to functional abnormalities. In combination with existing adult data, results of the proposed studies will establish normative patterns of development in auditory cortical fields, and allow correlations to be drawn between stages of structural maturity, and the onset of cortical function. Additionally, these data will provide a template against which patterns arising from periods of abnormal development may be compared.