Impaired autobiographical remembering and future thinking in temporal lobe epilepsy

The ability to imagine future events, episodic simulation (ES), is critical for goal setting and adaptive functioning. Although ES engages many of the same neural substrates as episodic memory (EM) in healthy controls, particularly the hippocampus, its disruption in clinical populations remains poorly characterized. Temporal lobe epilepsy (TLE) is a condition marked by mesial temporal pathology and known EM impairments. However, both the relationships between EM and ES deficits and their hippocampal structural correlates remain unexplored. Here, we tested whether TLE is associated with impoverished ES beyond EM and language impairments and evaluated the relationship between ES and hippocampal morphology.

We assessed patients with drug-resistant TLE and controls using the adapted autobiographical interview and hippocampal morphometry (subfield volume, thickness, and gyrification) derived from HippUnfold.

TLE patients exhibited marked deficits in internal detail generation for both past and future events, even after controlling for verbal output. Performance on episodic memory and simulation showed weak coupling in TLE. Left TLE patients showed uniformly reduced internal detail generation, while right TLE patients retained a past-future gradient. Subfield volumes (left CA1 and right CA2/3) predicted EM performance in right TLE only, whereas left hippocampal gyrification predicted performance across both EM and ES. The cluster predicting ES was more specific, as whole hippocampal gyrification predicted EM but not ES.

These findings reveal overlapping but differing hippocampal correlates for deficits in remembering and imagining episodic details in TLE and underscore the clinical relevance of assessing future-oriented cognition.