Mechanisms of visual cortical development

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DESCRIPTION (provided by applicant): Beginning before eye opening and continuing in the mature adult brain, neuronal activity within the visual pathway plays a prominent but changing role. Before eye opening and during the critical period of early visual system development, spontaneous and visually driven activity play a primary role in the establishment and stabilization of early synaptic connections. In the mature brain, neuronal activity provides the underlying substrate for the detection and coding of sensory input. The proposed experiments will focus on investigating and manipulating the correlational and statistical properties of neuronal activity within the visual pathway throughout this period of time. First, multielectrode recording will be utilized to assess the correlational structure of spontaneous and visually driven activity within the LGN and visual cortex of P24 to adult awake behaving normally reared ferrets. Second, the role of spatio-temporally patterned activity in the maturation of orientation selectivity will be examined. It has been shown that different forms of early visual experience differentially alter the development of orientation selectivity and orientation preference maps. While it is believed that these alterations are driven by changes in the correlational structure of activity within the visual pathway, the neural basis of these changes has not been directly examined. Utilizing chronically implanted multielectrode recording arrays in awake behaving ferrets, the correlational structure of neuronal activity within the LGN and visual cortex will be compared under a variety of different rearing conditions including dark rearing and binocular lid suture. The effect of altering the spatio-temporal correlational structure of visual experience will be directly assessed by raising animals with miniature head mounted LCD displays. These displays will allow the chronic presentation of dynamical computer generated patterns containing varying short and long-range spatial and temporal correlations. Finally, changes in the coding of visual stimuli by single cells and cell ensembles within the developing visual cortex and LGN will be investigated. While the development of basic cortical tuning properties such as orientation selectivity is well studied, the emergence of more complex properties of visual cortical coding in the mature brain remains unclear. Coding properties such as sparseness, information capacity, and mutual information and redundancy will be assessed during post eye-opening development. These experiments should provide new information about the development of mechanisms underlying sensory coding within the brain.