Sleep Selectively Enhances Memory Expected to Be of Future Relevance

Abstract

The brain encodes huge amounts of information, but only a small fraction is stored for a longer time. There is now compelling evidence that the long-term storage of memories preferentially occurs during sleep. However, the factors mediating the selectivity of sleepassociated memory consolidation are poorly understood. Here, we show that the mere expectancy that a memory will be used in a future test determines whether or not sleep significantly benefits consolidation of this memory. Human subjects learned declarative memories (word paired associates) before retention periods of sleep or wakefulness. Postlearning sleep compared with wakefulness produced a strong improvement at delayed retrieval only if the subjects had been informed about the retrieval test after the learning period. If they had not been informed, retrieval after retention sleep did not differ from that after the wake retention interval. Retention during the wake intervals was not affected by retrieval expectancy. Retrieval expectancy also enhanced sleep-associated consolidation of visuospatial (two-dimensional object location task) and procedural motor memories (finger sequence tapping). Subjects expecting the retrieval displayed a robust increase in slow oscillation activity and sleep spindle count during postlearning slow-wave sleep (SWS). Sleepassociated consolidation of declarative memory was strongly correlated to slow oscillation activity and spindle count, but only if the subjects expected the retrieval test. In conclusion, our work shows that sleep preferentially benefits consolidation of memories that are relevant for future behavior, presumably through a SWS-dependent reprocessing of these memories.

Influence of reward motivation on human declarative memory

“…Thus, reward does not only support memory consolidation by increasing neuroplasticity in the hippocampus via dopamine release at encoding, but also by potentiating selective replay during sleep after encoding (Singer and Frank, 2009), recently confirmed also by optogenetic stimulation of mouse dopamine VTA-dorsal hippocampus pathway at encoding which enhanced spatial memory and increased reactivation of the stimulated neurons during sharp-wave ripples in post-encoding sleep (McNamara et al, 2014). In fact in humans, reward association or expectation has been shown to boost sleep-related gains in memory (Fischer and Born, 2009;Oudiette et al, 2013;Wilhelm et al, 2011;Igloi et al 2015). Reward circuits may play a role not only in selective memory consolidation during sleep, but also in the generation of dreams.…”

Neuroscience and education: prime time to build the bridge

“…In addition, a large body of knowledge has accumulated that shows that sleep enhances memory processing and, conversely, that sleep disruption can result in major learning deficits 12,13 . In humans, sleep after memory acquisition has been shown to benefit the consolidation 14 , restructuring 15 , generalization and selective remembering of memories 16 . These psychological discoveries have been paralleled by human imaging studies showing that the reactivation and neuroanatomical reorganization of memory traces are favored by sleep and proportional to learning 12 .…”

Sleep restriction can attenuate prioritization benefits on declarative memory consolidation

“…While several factors can lead to stimuli being tagged as important to remember (Oudiette and Paller, 2013), of particular relevance to the present study is work showing that the sleep‐dependent gain in motor performance is greater for sequences associated with a monetary reward relative to those that are not (Fischer and Born, 2009). Similarly, simply the expectancy of a memory test can lead to sleep‐dependent gains in declarative, procedural, and visuospatial memory (Van Dongen et al ., 2012; Wilhelm et al ., 2011). …”