FY2013 has seen significant progress towards establishing the research infrastructure and towards realizing these goals and objectives. We have developed our lab infrastructure for capturing and analyzing intracranial recordings while participants engage in cognitive tasks designed to probe memory encoding and retrieval. Patients with medically refractory epilepsy receiving intracranial electrodes and surgical treatment at the Clinical Center have been recruited for these studies. In one set of studies, we have principally been interested in investigating whether patterns of neuronal oscillatory power are reinstated from memory encoding to memory retrieval, and in examining the precise spatiotemporal dynamics of such reinstatement. Using a paired associates episodic memory task, we have directly examined these questions. We have first examined the changes observed in oscillatory activity during memory encoding. We then implemented analysis techniques that aggregate the distributed pattern of oscillatory power across multiple cortical locations and across multiple frequency bands in order to probe whether this activity is reinstated during recall. We have demonstrated that, during successful recall, there is significantly greater reinstatement of this pattern of oscillatory power across space and across frequencies. Furthermore, we have developed analyses that demonstrate the precise timing of such oscillatory activity and reinstatement across individual frequencies and locations. In a second set of studies, we have been principally interested in understanding how attentional mechanisms mediate the formation of successful memories. We have designed a behavioral task that specifically asks this question and allows us to compare neural activity between items that are attended to and successfully remembered versus those that were not attended to yet still remembered. Our interest is in understanding how attention itself mediates memory. Based on our preliminary analyses from several participants, we have found clear evidence that attentional cues significantly trigger neural activity in precise spatial locations that correlate with successful memory encoding. We have also developed and continued our work in capturing and analyzing local field potential and single unit spiking activity captured from the basal ganglia during deep brain stimulation surgery. We have focused on activity in the subthalamic nucleus in order to understand the role this structure plays in mediating decision conflict as participants performed perceptual decision tasks. We have demonstrated that decision periods are marked by significant increases in theta oscillatory power in the subthalamic nucleus, and that these oscillations are significantly stronger during decisions that involve greater conflict. Furthermore, directed coherence between the prefrontal cortex, measured using scalp EEG, and the subthalamic nucleus is significantly higher when subjects are mediating high conflict decisions. These data suggest that theta oscillatory activity may communicate information from the cortex to the basal ganglia during decision processes. We have extended this work to investigate the role of subthalamic nucleus single-unit spiking activity and how this activity relates to the observed changes in oscillatory power. We have identified distinct neuronal populations that exhibit different temporal dynamics that are differentially mediated by conflict. Importantly, we have shown that spiking activity in these populations of neurons is entrained by theta and beta oscillations, suggesting that the cortical oscillations used to convey information regarding decision conflict to the subthalamic nucleus ultimately modulate spiking activity in that structure. We have designed a new set of experiments to build upon these findings and to directly measure prefrontal cortical activity using intracranial subdural electrodes temporarily placed during DBS surgery in order to precisely understand how these structures communicate.
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