Sleep-Induced Changes in Associative Memory

Abstract

The notion that dreaming might alter the strength of associative links in memory was first proposed almost 200 years ago. But no strong evidence of such altered associative links has been obtained. Semantic priming can be used to quantify the strength of associative links between pairs of words; it is thought to measure the automatic spread of activation from a "node" representing one word to nodes representing semantically related words. Semantic priming could thus be used to test for global alterations in the strengths of associative links across the wake-sleep cycle. Awakenings from REM and nonREM (NREM) sleep produce a period of state carry-over during which performance is altered as a result of the brain's slow transition to full wakefulness, and cognitive testing in this period can provide information about the functioning of the brain during the prior sleep period. When subjects were tested across the night--before and after a night's sleep as well as immediately following forced awakenings from REM and NREM sleep--weak priming (e. g., thief-wrong) was found to be state dependent (p = 0.016), whereas strong priming (e.g., hot-cold) was not (p = 0.89). Weak primes were most effective in the presleep and REM sleep conditions and least effective in NREM and postsleep conditions. Most striking are analyses comparing weak and strong priming within each wake-sleep state. Contrary to the normal pattern of priming, subjects awakened from REM sleep showed greater priming by weak primes than by strong primes (p = 0.01). This result was seen in each of three protocols. In contrast, strong priming exceeded weak priming in NREM sleep. The shift in weak priming seen after REM sleep awakenings suggests that cognition during REM sleep is qualitatively different from that of waking and NREM sleep and may reflect a shift in associative memory systems, a shift that we hypothesize underlies the bizarre and hyperassociative character of REM-sleep dreaming. Known changes in brainstem activity that control the transition into and maintenance of REM sleep provide a possible explanation of this shift.

Targeted memory reactivation of newly learned words during sleep triggers REM-mediated integration of new memories and existing knowledge

“…There is also a growing literature on the association between REM and declarative memory processes that go beyond strengthening new episodic memories. For instance, REM has been associated with increased semantic priming of distantly related pairs of words (Stickgold, Scott, Rittenhouse & Hobson, 1999;Carr & Nielesen, 2015), problem solving through activation of broad associative semantic networks (Walker, Liston, Hobson & Stickgold, 2002;Cai et al, 2009), and extraction of statistical patterns in learning (Barsky et al, 2015). Our data are consistent with the view that REM activates broad semantic networks and allows the integration of new memories with remotely related existing knowledge.…”

A Sampler of Event-Related Brain Potential (ERP) Analyses of Language Processing

“…Less apparent is why during PS the ERPs to pseudowords, but not incongruous words, resembled those to congruous words. The authors suggest that these results are consistent with the finding by Stickgold, Scott, rittenhouse, & Hobson (1999) that linguistic absurdity is accepted in a different manner in dream-sleep than during waking, as reflected by an abnormal pattern of semantic behavioral priming (upon being awoken from PS) where weak primes show greater effects than strong primes. However, it is unclear why this pattern, for which the equivalent in the Perrin study would be reduced N400s to more weakly associated words, would not also hold for the incongruous words as well as for the pseudowords.…”

Sleep and Emotional Functions

“…4), sleep deprivation (SD) impairs affectively guided decision making (Pace-Schott et al 2012), moral reasoning ), insight (Wagner et al 2004), and creativity (Cai et al 2009;Home 1988). Based on the 'carry-over effect' after awakening (during which performance is altered as a result of the brain's slow transition to full wakefulness), elegant studies by Stickgold and colleagues showed that subjects awoken from REM sleep had a 32 % advantage in the number of anagrams solved (Walker et al 2002) and also showed greater priming by weak primes (e. g., thief-wrong) than by strong primes (e.g., hot-cold), contrary to the pattern of priming observed during wakefulness (Stickgold et al 1999). These data are consistent with a hyperassociative state of the mind during REM sleep.…”