Transient Epileptic Amnesia - Persistent Memory Effects - Remote Memory Loss

Remote Memory Loss

70% of people with TEA notice a patchy but persistent loss of memories of events from their past personal experiences and this autobiographical amnesia has been reported in all cases in which accelerated forgetting was also present. This memory loss can occur in people whose ability to acquire new memories is intact. Studying this 'autobiographical amnesia' or 'focal retrograde amnesia' or 'delayed onset amnesia' has been challenging because people do not always realize they have forgotten events or periods of time until they have difficulty in retrieving memories of specific significant events, and find they cannot form a coherent recollection. At first they might think they have forgotten some isolated events due to normal forgetting, and not realize they have forgotten larger blocks of past time:

"In our experience, patients most often present complaining of islands of memory loss that become apparent when discussing holidays or family events. We now ask patients with suspected TEA if they have gaps in their autobiographical memory, and especially about recall of holidays and other salient personal events. This is not, we would argue, because of the unique status of such events, but rather because it reflects the patchy nature of the remote memory deficit and the vulnerability of singular events. It is unlikely that a single week missing from everyday life would be noticed, owing to the repetitive nature of most day to day activities. In contrast, the loss of memory for last year’s holiday brings the retrograde memory loss into sharp relief."

These memory deficits have been shown to extend across the entire lifespan and there are significant impairments across a wide range of different types of contextual information including event, place, perceptual and thought/emotion details. When asked to produce personal memories relating to a particular word (for example, "boat"), a 68 year old epileptic patient failed to retrieve any episodes from his twenties or thirties. His performance on standard tests of anterograde memory was normal."

Autobiographical amnesia maybe caused by repeated seizures in the temporal lobe resulting in the progressive "erasure" of memories. Alternatively, autobiographical memory loss may result from subtle changes in the temporal lobe which gives rise to temporal lobe epilepsy and to memory problems. The mechanism and etiology of this phenomenon remains controversial, especially as it is impossible to rule out prior subclinical epileptic activity which could be responsible for a failure to consolidate those seemingly forgotten memories. A recent imaging study that aimed to provide insight into the neural basis of these autobiographical memory deficits revealed that patients had significantly reduced activation in the right medial temporal lobes (and more specifically the right posterior parahippocampal cortex)and effective connectivity analysis indicated that there was reduced connectivity between this right parahippocampal region and the right middle temporal gyrus, which has been linked to semantic memory

As well as these autobiographical memory deficits, patients have problems with personal semantic information (e.g., names of friends, jobs etc), particularly for mid-life events. Knowledge for public semantic information such as famous faces, famous events, or new word acquisition appears to be broadly intact. However, for semantic information that has an episodic component, such as knowledge of whether people are dead or alive, patients with TEA often show significant deficits.

Read more about this topic:  Transient Epileptic Amnesia, Persistent Memory Effects

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