Contributions of post-learning REM and NREM sleep to memory retrieval
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AbstractIt has become clear that sleep after learning has beneficial effects on the later retrieval of newly acquired memories. The neural mechanisms underlying these effects are becoming increasingly clear as well, particularly those of non-REM sleep. However, much is still unknown about the sleep and memory relationship: the sleep state or features of sleep physiology that associate with memory performance often vary by task or experimental design, and the nature of this variability is not entirely clear. This paper describes pertinent features of sleep physiology and provides a detailed review of the scientific literature indicating beneficial effects of post-learning sleep on memory retrieval. This paper additionally introduces a hypothesis which attributes these beneficial effects of post-learning sleep to separable processes of memory reinforcement and memory refinement whereby reinforcement supports one's ability to retrieve a given memory and refinement supports the precision of that memory retrieval in the context of competitive alternatives. It is observed that features of non-REM sleep are involved in a post-learning substantiation of memory representations that benefit memory performance; thus, memory reinforcement is primarily attributed to non-REM sleep. Memory refinement is primarily attributed to REM sleep given evidence of bidirectional synaptic plasticity in REM sleep and findings from studies of selective REM sleep deprivation.
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Testing a Hypothesis of Non-REM Sleep Reinforcement and REM Sleep Refinement for the Benefits of Post-Learning Sleep on Memory RetrievalMacDonald, Kevin John; Department of PsychologyIt is well established that post-learning sleep benefits later memory retrieval, but there is still much to learn about the processes involved and the nature of these benefits. Sleep is composed of stages of non-REM (NREM) and REM sleep: NREM sleep, especially slow wave activity of NREM sleep, and REM sleep have been implicated in memory performance benefits, but the specific contributions of each state remain unclear. This thesis presents a hypothesis proposing that post-learning NREM sleep supports memory accessibility, benefitting the likelihood of successful memory retrieval, and that post-learning REM sleep supports memory fidelity, allowing for more accurate retrieval when retrieval is successful. This hypothesis was tested over studies examining the effects of an afternoon nap (Chapter 2), targeted memory reactivation during NREM slow wave sleep (Chapter 3), and both targeted memory reactivation during NREM slow wave sleep and selective deprivation of REM sleep (Chapter 4) on measures of memory accessibility and memory fidelity in visuospatial memory tasks. In each study, measures of sleep architecture and electroencephalographic power in sleep were examined as predictors of memory performance. Several identified associations and interactions further inform an understanding of how NREM sleep and REM sleep may benefit memory performance. Most notably, these studies consistently found greater slow wave activity of NREM sleep to be specifically associated with better maintenance of memory accessibility. These studies did not identify a clear effect of REM sleep. It is hoped that the hypothesis and findings presented stimulate additional inquires that will further our understanding of the individual and combined contributions of NREM and REM sleep.
Subjective, behavioural and electrophysiological measurements of the time-course and intensity of sleep inertia after a full night of sleep /Stewart, Craig P.; Department of Psychology (Brock University, 2000-07-14)Several recent studies have described the period of impaired alertness and performance known as sleep inertia that occurs upon awakening from a full night of sleep. They report that sleep inertia dissipates in a saturating exponential manner, the exact time course being task dependent, but generally persisting for one to two hours. A number of factors, including sleep architecture, sleep depth and circadian variables are also thought to affect the duration and intensity. The present study sought to replicate their findings for subjective alertness and reaction time and also to examine electrophysiological changes through the use of event-related potentials (ERPs). Secondly, several sleep parameters were examined for potential effects on the initial intensity of sleep inertia. Ten participants spent two consecutive nights and subsequent mornings in the sleep lab. Sleep architecture was recorded for a fiiU nocturnal episode of sleep based on participants' habitual sleep patterns. Subjective alertness and performance was measured for a 90-minute period after awakening. Alertness was measured every five minutes using the Stanford Sleepiness Scale (SSS) and a visual analogue scale (VAS) of sleepiness. An auditory tone also served as the target stimulus for an oddball task designed to examine the NlOO and P300 components ofthe ERP waveform. The five-minute oddball task was presented at 15-minute intervals over the initial 90-minutes after awakening to obtain six measures of average RT and amplitude and latency for NlOO and P300. Standard polysomnographic recording were used to obtain digital EEG and describe the night of sleep. Power spectral analyses (FFT) were used to calculate slow wave activity (SWA) as a measure of sleep depth for the whole night, 90-minutes before awakening and five minutes before awakening.
An electrophysiological examination of intentional and inadvertent sleep onset : the effect of intention on the sleep onset processMurphy, Tim.; Department of Psychology (Brock University, 1995-07-09)The main purpose ofthis study was to examine the effect ofintention on the sleep onset process from an electrophysiological point ofview. To test this, two nap conditions, the Multiple Sleep Latency Test (MSLT) and the Repeated Test of Sustained Wakefulness (RTSW) were used to compare intentional and inadvertent sleep onset. Sixteen female participants (aged 19-25) spent two non-consecutive nights in the sleep lab; however, due to physical and technical difficulties only 8 participants produced compete sets of data for analysis. Each night participants were given six nap opportunities. For three ofthese naps they were instructed to fall asleep (MSLT), for the remaining three naps they were to attempt to remain awake (RTSW). These two types of nap opportunities represented the conditions ofintentional (MSLT) and inadvertent (RTSW) sleep onset. Several other sleepiness, performance, arousal and questionnaire measures were obtained to evaluate and/or control for demand characteristics, subjective effort and mental activity during the nap tests. The nap opportunities were scored using a new 9 stage scoring system developed by Hori et al. (1994). Power spectral analyses (FFT) were also performed on the sleep onset data provided by the two nap conditions. Longer sleep onset latencies (approximately 1.25 minutes) were obseIVed in the RTSW than the MSLT. A higher incidence of structured mental activity was reported in the RTSW and may have been reflected in higher Beta power during the RTSW. The decent into sleep was more ragged in the RTSW as evidenced by an increased number shifts towards higher arousal as measured using the Hori 9 stage sleep scoring method. 1ll The sleep onset process also appears to be altered by the intention to remain awake, at least until the point ofinitial Stage 2 sleep (i.e. the first appearance of spindle activity). When only examining the final 4.3 minutes ofthe sleep onset process (ending with spindle activity), there were significant interactions between the type ofnap and the time until sleep onset for Theta, Alpha and Beta power. That is to say, the pattern of spectral power measurements in these bands differed across time as a function ofthe type ofnap. The effect ofintention however, was quite small (,,2 < .04) when compared to the variance which could be accounted for by the passage oftime (,,2 == .10 to .59). These data indicate that intention alone cannot greatly extend voluntary wakefulness if a person is sleepy. This has serious implications for people who may be required to perform dangerous tasks while sleepy, particularly for people who are in a situation that does not allow them the opportunity to engage in behavioural strategies in order to maintain their arousal.