Abstracts

Rationale: Epilepsy has long been known to impact both short- and long-term memory. In more recent years, a specific long-term memory deficit known as Accelerated Long-Term Forgetting (ALF) has been commonly described in temporal lobe epilepsy patients (TLE). ALF is characterized by what appears to be a normal initial retention of learned information, followed by an accelerated rate of memory decay (Kapur et al., Brain Cogn 1997), and impacts both recall and recognition of previously learned information (Narayanan et al., Epilepsy Behav 2012). However, the precise point at which ALF becomes pathologic is still unclear, as delay intervals and memory types vary across research designs in the literature. Thus, we aimed to quantify and characterize long-term memory in epilepsy using a video task.

Methods: Subjects undergoing EEG monitoring watched a documentary then were tested on their retrieval of the film’s episodic, visual and verbal content immediately after viewing and at delay points of 24, 48, and 72 hours. In order to test both recall and recognition memory, subjects were able to choose their question style for each question presented; if subjects felt certain of their ability to accurately retrieve their answer, they could choose to freely type their response (a test of recall) or if they were less certain, they could opt for a multiple choice selection (a test of recognition). Additionally, participants answered a 7-point Likert scale about their answer confidence after each recognition question.

Results: Our preliminary results show a significant effect of subject type on question choice. Epilepsy subjects chose to recall at higher rates than controls at both baseline and 24 hours. Despite this higher confidence in recall ability reflected in question choice, baseline recall accuracy was significantly worse than controls. There was also a significant effect of delay on question choice, with a shift to more recognition questions from baseline to 24 hours and from 24 to 48 hours. In order to assess ALF, we calculated forgetting rates (percent accuracy relative to baseline performance) for each delay point. For recognition memory, we did not find an impact of either delay or subject type on forgetting. However, for recall forgetting there was a significant effect of both subject type and delay. Epilepsy subjects had higher rates of recall forgetting, particularly at 72 hours.

Conclusions: Overall, subjects with epilepsy display both subjective and objective memory deficits over the course of a 72-hour delay. Epilepsy subjects displayed high certainty of their memory by their decision to recall at higher rates than controls. However, their recall accuracy is significantly worse, and thus this high rate of “false positives” in recall memory reflects false familiarity (Martin et al., Memory 2019). Thus, these subjects are showing misplaced certainty of their answers due to a false belief that they are familiar with the question at hand. Finally, epilepsy subjects exhibited ALF at the 72-hour delay point for recall, but not recognition, memory. These results further support the need for more effective therapies aimed at improving memory in epilepsy.

Funding: Please list any funding that was received in support of this abstract.: NSF EPSCOR Grant (1632738).