Accelerated forgetting in focal epilepsy: Rates and underlying factors

Miller, L. 1, 2 & Ricci, M. 3

1 Neuropsychology Unit, Royal Prince Alfred Hospital, Sydney, Australia
2 ARC Centre of Excellence in Cognition and Its Disorders, University of Sydney, Sydney Australia
3 ARC Centre of Excellence in Cognition and Its Disorders, Macquarie University , Sydney, Australia

Accelerated long-term forgetting (ALF) is a recently recognised phenomenon whereby a person shows normal memory at shorter delays (e.g., 30 min) but deficient memory days or weeks later. The factors underlying this phenomenon and its rate of occurrence in patients with focal epilepsy are not known. We examined recall of (1) an autobiographical experience (AE) and (2) a story learned-to-criterion at short (30 min) and longer-term (4 day) delays in 21 patients with temporal lobe epilepsy (TLE), 11 patients with extratemporal epilepsy (ETE) and 29 age- and education-matched normal control subjects. ALF was defined as having a memory Z score greater than -1.5 at 30 min and lower than -1.5 at 4 days. We found that rates of ALF were similar for the two types of material and for the two patient groups (~20%). Illness duration was correlated with ALF for both AE and story memory. ALF of the experience was also associated with epileptiform discharges during the delay, higher seizure frequency, symptoms of depression and presence of a hippocampal lesion, with the last variable (hippocampal lesion) proving the most important predictor. These findings clarify the frequency of occurrence and factors contributing to impaired long-term consolidation.