Abstracts

Rationale: Long-term memory difficulties are commonly reported by people with epilepsy.¹ However, the underlying mechanisms of these deficits are not known.There is a two-step theory of memory formation that assumes a consolidation phase follows an initial learning phase. Memory consolidation has been suggested to occur predominantly during sleep, ² and specifically slow wave sleep (SWS). The hierarchical nesting of slow oscillations, spindles, and ripples during SWS has been proposed to provide the temporal framework for consolidation of long-term memory by shuttling the newly formed memories from the hippocampus, where the memory forms, to the neocortex, where the memory is stored.³ All of these different classes of neural oscillations are also impacted by epilepsy.We hypothesized that sleep would not benefit memory retention in people with epilepsy. To test it, we compared the epilepsy patients’ performance on a sleep-sensitive verbal memory task over two conditions, sleep and wakeful retention intervals. Methods: We studied the long-term memory performance, in people with epilepsy (n=5) who were admitted to the adult EMU for seizure classification/localization. Sleep leads were added to the conventional scalp EEG. The study had two phases – learning and retrieval. We used a Paired-Associated Learning (PAL) task, which assesses verbal declarative learning (left hippocampus) and proven to be sensitive to effects of sleep 2. Each of the wordlists consisted of 46 pairs of English nouns. The type of retrieval task was cued recall. During the learning, the initial presentation of word-pairs was followed by loops of cued recalls with feedback until a minimum of 60% correct responses reached. To prevent serial learning, the sequence of word-pair presentations within the lists was randomized between repeated trials. Subjects were tested immediately after the learning phase (criterion trial) and also after a two-hour retention interval. The retention intervals consisted of a two-hour “nap” on the sleep day, and a two-hour period of wakefulness on a control day (random crossover on two subsequent days). All subjects participated in both nap and control testing conditions.We used the Digit Span test of the WAIS and the Positive and Negative Affect Schedule (PANAS) test before the learning and after the recall to assess working memory and subjects' current mood. Sleep scoring was performed according to AASM2012 rules Results: “Retention Performance” was defined by the percentage of recalled word pairs during the retrieval test after the retention interval, with performance on the criterion trial was set to 100%. “Retention Performance” compared between the two conditions of sleep and wakefulness. All of the participants had some periods of SWS during the “nap” retention interval; however, the “Retention Performance” was not significantly different between the sleep and wakeful conditions (p-value>0.05). Conclusions: Slow wave sleep (SWS) did not benefit memory retention in the people with epilepsy studied here. We proposed that sleep-dependent memory consolidation is impaired in epilepsy patients and may underlie their long-term memory deficits. Evaluation of sleep-dependent memory consolidation in control subjects without epilepsy is underway. Moving forward, we hope that through the interventions during deep sleep, we will be able to enhance memory consolidation and improve long-term memory in people with epilepsy. References1) Brain. 2008;131(Pt 9):2243-2263. 2) Sleep Med Rev. 2009;13(5):309-321.3) Nat Neurosci. 2015;18(11):1679-1686. Funding: Mayo ClinicEuropean Regional Development Fund: FNUSA-ICRC (No. CZ.1.05/1.1.00/02.0123)