Sleep disturbance in PTSD and other anxiety-related disorders: an updated review of clinical features, physiological characteristics, and psychological and neurobiological mechanisms.

Napping benefits long-term memory formation and is a tool many individuals use to improve daytime functioning. Despite its potential advantages, approximately 47% of people in the United States eschew napping. The goal of this study was to determine whether people who endorse napping at least once a week (nap+) show differences in nap outcomes, including nap-dependent memory consolidation, compared with people who rarely or never nap (nap-). Additionally, we tested whether four weeks of nap practice or restriction would change sleep and performance profiles. Using a perceptual learning task, we found that napping enhanced performance to a greater degree in nap+ compared with nap- individuals (at baseline). Additionally, performance change was associated with different electrophysiological sleep features in each group. In the nap+ group, spindle density was positively correlated with performance improvement, an effect specific to spindles in the hemisphere contralateral to the trained visual field. In the nap- group, slow oscillatory power (0.5-1 Hz) was correlated with performance. Surprisingly, no changes to performance or brain activity during sleep emerged after four weeks of nap practice or restriction. These results suggest that individual differences may impact the potential benefits of napping on performance and the ability to become a better napper.

/pdf/the-impact-of-frequent-napping-and-nap-practice-on-sleep-3s7l1r7f8p.pdf

The impact of frequent napping and nap practice on sleep-dependent memory in humans.

It has been known since the time of patient H.M. and Karl Lashley’s equipotentiality studies that the hippocampus and cortex serve mnestic functions. Current memory models maintain that these two brain structures accomplish unique, but interactive, memory functions. Specifically, most modeling suggests that memories are rapidly acquired during waking experience by the hippocampus, before being later consolidated into the cortex for long-term storage. Sleep has been shown to be critical for the transfer and consolidation of memories in the cortex. Like memory consolidation, a role for sleep in adaptive forgetting has both historical precedent, as Francis Crick suggested in 1983 that sleep was for ‘reverse-learning’, and recent empirical support. In this article I review the evidence indicating that the same brain activity involved in sleep replay associated memory consolidation is responsible for sleep-dependent forgetting. In reviewing the literature, it became clear that both a cellular mechanism for systems consolidation and an agreed upon general, as well as cellular, mechanism for sleep-dependent forgetting is seldom discussed or is lacking. I advocate here for a candidate cellular systems consolidation mechanism wherein changes in calcium kinetics and the activation of consolidative signaling cascades arise from the triple phase locking of NREMS slow oscillation, sleep spindle and sharp-wave ripple rhythms. I go on to speculatively consider several sleep stage specific forgetting mechanisms and conclude by discussing a notional function of NREM-REMS cycling. The discussed model argues that the cyclical organization of sleep functions to first lay down and edit and then stabilize and integrate engrams. All things considered, it is increasingly clear that hallmark sleep stage rhythms, including several NREMS oscillations and the REMS hippocampal theta rhythm, serve the dual function of enabling simultaneous memory consolidation and adaptive forgetting. Specifically, the same sleep rhythms that consolidate new memories, in the cortex and hippocampus, simultaneously organize the adaptive forgetting of older memories in these brain regions.

/pdf/remembering-to-forget-a-dual-role-for-sleep-oscillations-in-1q05i3ypj0.pdf

Remembering to Forget: A Dual Role for Sleep Oscillations in Memory Consolidation and Forgetting.

https://escholarship.org/content/qt5qf8z7vf/qt5qf8z7vf.pdf?t=ozsbm2

The effect of sex and menstrual phase on memory formation during a nap

Memories selectively benefit from sleep. In addition to the importance of the consolidation of relevant memories, the capacity to forget unwanted memories is also crucial. We investigated the effect of suppressing unwanted memories on electroencephalography activity of subsequent sleep using a motivated forgetting (MF) paradigm as compared with a control non-forgetting task. Subjects were randomly assigned to nap or no-nap groups. We used a modified version of the think/no-think paradigm with dominant number of no-think words cued to be forgotten and included only subjects capable of suppressing unwanted memories by performing an initial subject inclusion experiment. In both groups and conditions, the performance of the subjects in recalling the word pairs learned in the beginning of the day was evaluated in a final recall test. We found that both nap and no-nap groups recalled significantly less no-think words in the MF condition compared to the control condition. Moreover, for the nap group, in the MF compared to the control condition, spindle power and density increased during stage 2 (S2) whereas they decreased during slow wave sleep (SWS). Interestingly, recall performance of no-think words was negatively correlated with spindle power during S2 whereas it was positively correlated with spindle power during SWS. These results indicate that sleep spindles are sensitive to the previous MF experiences and suggest a differential role of sleep spindles during S2 and SWS in memory processing during sleep.

Opposite effect of motivated forgetting on sleep spindles during stage 2 and slow wave sleep

A well-established literature supports a critical role of sleep for learning and memory (Abel et al. in Curr Biol 23(17);R774–R788, 2013; Diekelmann and Born in Nat Rev Neurosci 11(2):114–126, 2010; Rasch and Born in Physiol Rev 93(2):681–766, 2013; Tononi and Cirelli in Sleep Med Rev 10(1):49–62, 2014). Studies have demonstrated memory improvements following a period of sleep compared to an equivalent time awake, and specific sleep features have been shown to correlate with improvements in discrete memory domains. For example, overnight procedural motor learning correlates with the amount of stage 2 sleep (Walker et al. in Neuron 35(1):205–211, 2002; Learn Mem 10(4):275–284, 2003), non-hippocampal dependent perceptual learning correlates with the product of the amount of slow wave sleep (SWS) and rapid eye movement (REM) sleep (Mednick et al. in Nat Neurosci 6(7):697–698, 2003; Stickgold et al. in J Cogn Neurosci 12(2):246–254, 2000), and implicit priming also appears to depend on REM sleep (Cai et al. in Proc Natl Acad Sci U S A 106(25);10130–10134, 2009). One feature of sleep that is widely implicated in memory processing is the sleep spindle, short (0.5–3 s) bursts of oscillatory activity in the frequency range of approximately 12–15 Hz (Spindles have also been defined as slow as 8–12 Hz, with some indication that these slow spindles may be physiologically distinct from alpha frequency, which oscillates in the same frequency range (8–12 Hz) but has a different spatial distribution (Manshanden et al. in Clin Neurophysiol 113(12):1937–1947, 2002). However, more data is required to determine the distinctiveness of these two signals. For the purpose of this chapter, we will primarily discuss spindles defined as ~12–15 Hz.). This chapter aims to (1) summarize correlational and causal evidence supporting the role of sleep spindles in memory processing; and (2) describe spindle dynamics and how they may be related to proposed mechanisms of sleep-dependent consolidation.

The Role of Sleep Spindles in Sleep-Dependent Memory Consolidation

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The Role of Sleep Spindles in Sleep-Dependent Memory Consolidation