Abstract
We investigated whether the benefit of slow wave sleep (SWS) for memory consolidation typically observed in healthy individuals is disrupted in people with accelerated long-term forgetting (ALF) due to epilepsy. SWS is thought to play an active role in declarative memory in healthy individuals and, furthermore, electrographic epileptiform activity is often more prevalent during SWS than during wakefulness or other sleep stages. We studied the relationship between SWS and the benefit of sleep for memory retention using a word-pair associates task. In both the ALF and the healthy control groups, sleep conferred a memory benefit. However, the relationship between the amount of SWS and sleep-related memory benefits differed significantly between the groups. In healthy participants, the amount of SWS correlated positively with sleep-related memory benefits. In stark contrast, the more SWS, the smaller the sleep-related memory benefit in the ALF group. Therefore, contrary to its role in healthy people, SWS-associated brain activity appears to be deleterious for memory in patients with ALF.
Highlights
The participants demonstrated a benefit of sleep for memory retention over twelve hours, and this benefit was no smaller in magnitude for the patients than the controls
There was a benefit of sleep for memory retention over 12 h: there was an interaction between sleep condition and retrieval time point [F(1.64, 34.46) 1⁄4 5.76, p 1⁄4 .01], with participants performing significantly better in the sleep condition than the wake condition on the 12-h test (p 1⁄4 .002) but not on the final training test (p 1⁄4 .64) or the 30-min test (p 1⁄4 .78)
The benefit of sleep for memory retention was no smaller in magnitude for the patients than the controls: there was no significant interaction between sleep condition, retrieval time point and group [F(1.64, 34.46) 1⁄4 .43, p 1⁄4 .62]
Summary
People with ALF appear to learn and initially retain new information normally, but subsequently forget at an accelerated rate (Bell & Giovagnoli, 2007; Butler & Zeman, 2008). This phenomenon provides a novel opportunity to investigate post-encoding memory processes. Post-encoding sleep is thought to play an important role in memory. This role is not fully understood, but may have both passive and active components. Sleep provides a temporary shield from potentially interfering cognitive stimulation. Cognitive stimulation during a wakeful retention interval may cause forgetting through a number of mechanisms e interference with access at the point of retrieval (e.g., Brown, Neath, & Chater, 2007); disruption of the memory trace (e.g., Wixted, 2004, 2010); and interference with certain consolidation processes (e.g., Mednick, Cai, Shuman, Anagnostaras, & Wixted, 2011; Wixted, 2004) e and so some part of sleep's benefit for memory retention is likely due to protection from this retroactive interference
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