NEURONAL SYNCHRONIZATION IN THE MEDIAL TEMPORAL LOBE AND MEMORY FORMATION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Damage to medial temporal lobe structures in monkeys impairs performance on a task of visual recognition memory, the Visual Preferential Looking Task (VPLT). This project seeks to identify the neuronal mechanisms that support memory performance on the VPLT in awake, behaving monkeys. In the past year, we finished data collection and analyses which demonstrated that increased gamma-frequency (40-100 Hz) synchronization among hippocampal neurons is associated with enhanced recognition memory. We showed, on a trial-by-trial basis, that Increased synchrony during encoding predicts successful subsequent recognition memory performance. We have also completed analyses that demonstrate that individual hippocampal neurons modulate their firing rates based on stimulus novelty. Furthermore, the magnitude of this modulation is correlated with recognition memory performance. Together, these studies suggest that hippocampal mechanisms, both at the single neuron and network level, underlie successful recognition memory. Finally, we have recently collected data that demonstrate the existence of theta-band oscillations in the primate hippocampus, and that the phase of these oscillations is reset by eye-movements during visual exploration. In addition, our recent data showed that theta-band phase modulates the power of gamma-band activity. Together, these data suggest that phase resetting of the theta-band oscillation to an 'ideal phase' upon fixation onset may align hippocampal activity to an optimal state with respect to gamma-band synchronization and memory formation.