Determinants of autobiographical memory in patients with unilateral temporal lobe epilepsy or excisions

Patients with unilateral temporal lobe epilepsy from hippocampal origin and patients with unilateral surgical excision of an epileptic focus located in the medial temporal lobe were compared to healthy controls on a version of the Autobiographical Interview (AI) adapted to assess memory for event-specific and generic personal episodes. For both types of episodes, patients with unilateral (left and right) temporal lobe epilepsy or excision (TLE) reported fewer internal details, which are bits of information pertaining to the recollected episode. The source of this deficit was mainly the paucity of perceptual information about the personal episodes, but temporal and spatial information was also deficient. Information about the episode's story elements was preserved in both AM conditions. Participants were also tested on a script generation task to assess retrieval of semantic information. Patients with TLE excision, but not pre-surgical patients, reported significantly fewer actions per script in comparison to controls, suggesting that the temporal neocortex is more involved than mesial temporal structures in recall of this type of information. Together, these results indicate that the hippocampus is essential to the recollection of sensory perceptual aspects of past experiences. Detailed story elements and gist information, as collected during the AI and the script generation task, respectively, are more resilient to hippocampal damage. The similarity of the impairment between the event-specific and the generic memory conditions also suggests that temporal specificity is not a key determinant of hippocampal engagement in autobiographical retrieval.