Transient Epileptic Amnesia

Abstract

Transient epileptic amnesia (TEA) is characterized by brief, recurrent episodes of transient amnesia occurring as a result of epilepsy. During these episodes, declarative memory is impaired while other cognitive functions remain intact. TEA is a syndrome of mesial temporal lobe epilepsy (TLE), which typically affects middle-aged people, particularly men. The amnesic attacks often occur on waking and can be accompanied by other symptoms of TLE such as automatisms, olfactory hallucinations, and short periods of unresponsiveness. EEG may reveal interictal epileptiform activity arising from the temporal lobes. Gross structural abnormalities are rarely observed, but group studies reveal subtle volume loss in hippocampal, perirhinal, and orbitofrontal cortices. The amnesic seizures respond very well to anticonvulsant medication, though most patients (around 80%) report interictal memory problems such as accelerated long-term forgetting (ALF), autobiographical, and topographical memory loss. These often persist despite successful treatment of the epilepsy. ALF, which is reported by around 50% of patients with TEA, involves the rapid forgetting of newly acquired information, occurs within 24 h of acquisition, and is likely to reflect a deficit in early memory consolidation or subtle impairments in memory acquisition. The autobiographical memory loss, seen in around two-thirds of patients with TEA, appears to be due to a degradation of established memories, though impairments of acquisition, consolidation, and retrieval may also play a part. These interictal memory difficulties are likely to result from either subtle structural damage in the medial temporal lobes or physiological disruption of memory processing by subclinical epileptiform activity.