Functional role of neural oscillations in attention and memory in humans

Synchronized oscillatory neural activity involving widespread neural ensemble is common in the central nervous system, and is hypothesized to enable the integration of various attributes of the sensory input, resulting in a unified percept. While activity evoked to external sensory input has been instantly recognized to reflect stimulus processing, ongoing neural activity preceding stimulus onset is often considered as background noise and irrelevant to subsequent stimulus processing. Our study seeks to advance the idea that ongoing neural oscillations are critical indices of the brain state and, as such, play an important role in stimulus-evoked cognitive processing. Applying advanced multivariate spectral analysis to invasive and non-invasive electrophysiological recordings from animals and humans, we address the mechanisms and the functional roles of synchronized prestimulus oscillatory activity in processes such as anticipatory attention, visual processing and encoding of memory.;First, applying computational techniques to invasive local field potential recordings from primates we expound the mechanisms leading to zero-lag synchrony across widely separated cortical areas, a phenomenon critically implicated in effective neuronal communication and thus higher-order perceptual processes. Second, we assessed the functional role of prestimulus theta band oscillation in memory related stimulus encoding in the human cortex using invasive electrocorticogram. Third, a physiological model linking prestimulus oscillations and stimulus-evoked response is proposed and is tested on non-invasive studies of human visual processing. Finally, the neural control of anticipatory attention and stimulus selection using electroencephalogram is investigated. The objective here is to expound the signals and the neural mechanisms that mediate these top-down processes that enable selective sensory integration during attentive behavior in humans.;In conclusion, our findings suggest that effective sensory-perceptual processing and thus cognitive and behavioral performance to an impending stimulus, depends on the excitability state of the brain defined by these neural oscillations at its onset. Further, it is shown that the prestimulus activity is not merely a random fluctuation in excitability but one that is actively controlled in a goal-directed manner through neural synchronization across widespread functionally relevant cortical networks. Thus, this study bolsters the functional role of prestimulus ongoing activity in subsequent sensory-perceptual and higher-order cognitive processing. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html)...