Neurophysiological Basis of fMRI

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DESCRIPTION (provided by applicant): Functional magnetic resonance imaging (fMRI) promises to provide the ability to pinpoint and track brain activity patterns underlying sensory, motor and cognitive skills, during their normal operation in intact subjects. However, this promise is thwarted by our inadequate understanding of the linkage between neural activity and fMRI signals, and by inherent limitations of current fMRI methods. We will investigate the neural basis of fMRI signals through experiments that combine high field fMRI with neural ensemble electrophysiology and pharmacology in monkeys; fMRI will be conducted with BOLD- and perfusion-sensitive protocols using a high-resolution, high signal-to-noise 7-Tesla system. Electrophysiology will utilize both scalp ERP recordings, and depth recordings with linear array multielectrodes, and will focus on ERP and current source density (CSD) measures as well as action potentials. CSD measures in particular, are essential for linking neural activity and fMRI. Neurochemical manipulation will entail both systemic infusions and intracortical microinfusions. Our specific aims are: 1. To Identify Neural Correlates of BOLD-fMRI: 2. To Optimize the Spatial and Temporal Resolution of fMRI 3. To Determine the Relationship of fMRI to ERPs and to Brain Processes. Initial studies will be conducted in anesthetized macaque monkeys & will focus on the cortical hand representation in Area 3b. Later studies will be implemented in awake monkeys & will be expanded to a few additional cortical regions. These studies will have the useful by-product of accurately describing the spatiotemporal activation pattern of the ascending somatosensory pathways from the hand surface in the macaque, and of doing so with methods that directly compare to those used in humans. This will help to bridge-the-gap between a vast single unit literature in monkeys, and a developing understanding of somatosensory structure and function in humans.