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Findings Show That Seizures during Sleep Can Scramble Memories

Findings Show That Seizures during Sleep Can Scramble Memories

A new study explains the reason why some people with epilepsy are likely to forget newly learnt information.

The brain, during sleep, replays newly learnt memories in a form of nocturnal rehearsal that strengthens the new information that the brain has recently processed. However, this mechanism has been found to be impaired in certain neurological groups, such as some patients with epilepsy who reportedly experienced ‘accelerated long-term forgetting’, in which forgetting becomes excessive only with some delay after initial learning.

A team of scientists from the Northwestern University, University of Michigan, and The University of Chicago have proposed that abnormal electrical activity in the hippocampus as a result of a seizure disorder could hamper memory storage.

Nine patients with temporal-lobe epilepsy underwent a spatial memory test before nocturnal sleep. Researchers played certain sounds while showing participants where on a screen certain pictures of common objects were located, and while the patients slept the sounds were played again in order to trigger associated memories. Results showed that the following morning, five patients without overnight seizure activity were able to recall object-locations revived by. However, four patients with seizure activity forgot cued object-locations.

According to the researchers, “Because memory was preferentially influenced for cued object-locations, rather than defective for all object-locations that had been learned, we suggest that overnight seizures specifically accelerated forgetting for exogenously reactivated memories. Given that this seizure activity was apparent unilaterally in the hippocampus, but not at the scalp, we speculate that this problem may impact patients with epilepsy even when standard scalp EEG recordings during sleep appear normal.”