The impact of epileptiform abnormalities and hippocampal lesions on retention of recent autobiographical experiences: adding insult to injury?

Accelerated long term forgetting (ALF), whereby information is rapidly lost over days or weeks has been noted in patients with epileptic conditions. The present study sought to determine which clinical factors underlie such consolidation failure for recent autobiographical experiences in patients with focal epilepsy. We enrolled 21 patients with temporal lobe epilepsy (TLE), with and without hippocampal lesions (TLE(+)=12; TLE(-)=9, respectively), 11 patients with extratemporal epilepsy (ETE) and 29 controls (NC). Recall and recognition were tested at different delays (i.e., 30. min, 24. h and 4 days). During the study interval, most of the patients underwent concurrent ambulatory EEG monitoring. Analyses of variance indicated Group×Delay interval interactions for recall. The TLE(+) group showed significant decline in recall by 24. h delay. On recognition Group by Delay interval was not detected but main effect for Group revealed that the ETE group demonstrated ALF on recognition questions over the interval between 24. h and 4 days. Regression analyses confirmed that a hippocampal lesion was particularly disruptive to consolidation over the first 24. h, and that seizures were associated with memory decline over longer delays. Our findings show that the retention of autobiographical experiences involves multiple mechanisms, which operate over different timeframes.