Research Post-Doctoral Fellow Dartmouth-Hitchcock Medical Center, New Hampshire
Rationale: Spatial memory impairment is commonly reported in people with epilepsy. We have previously shown that interictal epileptiform discharges (IEDs) are associated with transient episodic memory impairment. We suspect that IEDs may also play a role in impairment of spatial memory. We previously found that the incidence of IEDs can vary when stimuli are presented to human subjects. It has also been demonstrated that IEDs are suppressed while subjects were engaged in a driving task. These findings suggest that there is a relationship between navigation, attention, and IEDs. Here, we investigate whether hippocampal oscillations during human real-world navigation impact the incidence and precise timing of hippocampal IEDs. Methods: In this study, we recruited subjects with a chronically implanted neurostimulator (NeuroPace RNS) to perform a real-world navigation task. Following audible instructions, subjects alternated between walking and standing still within the Dartmouth-Hitchcock Medical Center Epilepsy Clinic. Simultaneously, intracranial EEG was recorded from the subjects' hippocampi using the neurostimulator. We used Watson's U2 test to measure whether there was a preferred phase of theta at which IEDs occurred, or whether the distribution was uniform over all phases. Results: We found that IEDs occurred at particular phases of theta while the subjects were navigating, but that there was no preferred phase while the subjects were standing still (p< 0.05, 421 IEDs, 5 subjects). The incidence of IEDs during navigation was not significantly different from the incidence while the subjects remained still (p >0.05,421 IEDs, 5 subjects). Conclusions: This finding indicates that there is a relationship between the phase of theta in the hippocampus and the likelihood of a hippocampal IED. Furthermore, this relationship is dependent on whether the subject is navigating. Further investigation is needed to determine whether spatial memory impairment is directly caused by IEDs. Funding: Please list any funding that was received in support of this abstract.: This project was funded by a Diamond Foundation Research Development Award, by DARPA (Collaborative Agreement N66001-14-2-4032), and by the National Science Foundation (Award #1632738).