Authors :
Rebecca Roth, BA – Emory University
Jarrod Marable, BS – Medical University of South Carolina
Jessica Decker, DO – Oregon Health & Science University
Jamie Lee, MD – Medical University of South Carolina
Nimit Desai, MD – Medical University of South Carolina
Marina Buciuc, MD – Medical University of South Carolina
Mattia Rosso, MD – Yale University
Daniel Drane, PhD – Emory University
Leonardo Bonilha, MD, PhD – University of South Carolina
Presenting Author: Ezequiel Gleichgerrcht, MD, PhD – Emory University
Rationale:
While episodic memory has been extensively studied in temporal lobe epilepsy (TLE), autobiographical memory in particular, especially episodic simulation—the ability to imagine future events—has received less attention. Yet, episodic simulation is crucial for functional independence, a sense of self, and overall well-being. Evidence suggests that episodic memory (retrieval) and simulation are supported by a common neural network. We investigated whether deficits in episodic memory in TLE extend to episodic simulation and examined the roles of anterior and posterior hippocampi in these processes.Methods:
We studied 18 controls and 31 patients with drug-resistant TLE (left n=17; right n=14). Participants completed an adapted autobiographical interview, asked to recall recent and distant episodic memories (autobiographical retrieval) and to imagine potential personal events in the near and distant future (episodic simulation). Control trials involved a picture description task without autobiographical content. Trials were randomized, recorded, transcribed verbatim, and scored using an automated algorithm. The primary dependent variable was the number of internal details, reflecting episodic content-specific detail generation during autobiographical retrieval and simulation. Participants also underwent 3T MRI scanning, and hippocampal volume was calculated for anterior and posterior subfields.Results:
We ran a 2 x 2 x 2 ANCOVA with group (control vs. patient), time direction (past vs. future), and temporal distance (near vs. far) as our 3 factors while controlling for mean picture description verbal output. Results showed significant differences in number of internal details produced by group [F(1, 46)=9.00, p=.004], time direction [F(1,535)=87.77, p< .001,] and verbal output [F(1,46)=79.58, p< .001] but not temporal distance independent of group [F(1,535)=1.58, p=0.21]. The interaction between group and time direction as was significant [F(1,535)=26.31, p< .001], and the interaction between group and temporal distance was significant [F(1,535)=6.18, p=.013], see Table 1. Next, we correlated left and right anterior and posterior hippocampal volumes with number of details produced. While controlling for verbal output, we observed a relationship between the number of internal details produced and left posterior hippocampal volume (r=0.45, p=0.006).
Conclusions:
Patients with TLE exhibited deficits in both episodic retrieval and simulation compared to controls. Controls produced more details for past events than future ones, consistent with existing literature. In contrast, TLE patients showed less variability across trials and fewer details overall, indicating impairments in both retrieval and simulation. Notably, left posterior hippocampal volume correlated with the number of internal details produced, underscoring its role in this cognitive process. Our findings confirm previous reports of episodic memory deficits in TLE and extend these to deficits in episodic simulation.
Funding:
Supported by awards UL1TR002378 (Georgia) and UL1TR001450 (South Carolina) as well as KL2TR002381 by the National Center for Advancing Translational Sciences (NCATS) of the National Institutes of Health (NIH).