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Sleep loss is associated with reduced health and quality of life, and increased risk of Alzheimer's disease and related dementias. Up to 66% of persons with Alzheimer's disease and related dementias experience poor sleep, which can predict or accelerate the progression of cognitive decline. Exercise is a widely accessible intervention for poor sleep that can protect against functional and cognitive decline. No previous systematic reviews have investigated the effectiveness of exercise for sleep in older adults with mild cognitive impairment or Alzheimer's disease and related dementias. We systematically reviewed controlled interventional studies of exercise targeting subjectively or objectively (polysomnography/actigraphy) assessed sleep in persons with mild cognitive impairment or Alzheimer's disease and related dementias. We conducted searches in PubMed, Embase, Scopus and Cochrane-Library (n = 6745). Nineteen randomised and one non-randomised controlled interventional trials were included, representing the experiences of 3278 persons with mild cognitive impairment or Alzheimer's disease and related dementias. Ten had low-risk, nine moderate-risk, and one high-risk of bias. Six studies with subjective and eight with objective sleep outcomes were meta-analysed (random-effects model). We found moderate- to high-quality evidence for the beneficial effects of exercise on self-reported and objectively-measured sleep outcomes in persons with mild cognitive impairment or Alzheimer's disease and related dementias. However, no studies examined key potential moderators of these effects, such as sex, napping or medication use. Our results have important implications for clinical practice. Sleep may be one of the most important modifiable risk factors for a range of health conditions, including cognitive decline and the progression of Alzheimer's disease and related dementias. Given our findings, clinicians may consider adding exercise as an effective intervention or adjuvant strategy for improving sleep in older persons with mild cognitive impairment or Alzheimer's disease and related dementias.

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Recent evidence suggests that the autonomic nervous system can contribute to memory consolidation during sleep. Whether fluctuations in cardiac autonomic activity during sleep following physical exercise contribute to the process of memory consolidation has not been studied. We assessed the effects of a non-rapid eye movement (NREM) nap following acute exercise on cardiac autonomic regulation assessed with heart rate variability (HRV) to examine if HRV influences memory processes. Fifty-six (59% female) healthy young adults (23.14 ± 3.74 years) were randomly allocated to either the exercise plus nap (ExNap, n = 27) or nap alone (NoExNap, n = 29) groups. The ExNap group performed a 40-minute moderate-intensity cycling, while the NoExNap group was sedentary prior to learning 45 neutral pictures for a later test. Subsequently, participants underwent a 60-minute NREM nap while measuring EKG, followed by a visual recognition test. Our results indicated that heart rate did not significantly differ between the groups (p = .243), whereas vagally mediated HRV indices were lower in the ExNap group compared to the NoExNap group (p < .05). There were no significant differences in sleep variables between the groups (p > .05). Recognition accuracy was significantly higher in the ExNap group than in the NoExNap group (p = .027). In addition, the recognition accuracy of the ExNap group was negatively associated with vagally mediated HRV (p < .05). Pre-nap acute exercise appears to attenuate parasympathetic activity and to alter the relationship between memory and cardiac autonomic activity.

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Recent evidence shows that a nap and acute exercise synergistically enhanced memory. Additionally, human-based cross-sectional studies and animal experiments suggest that physical exercise may mitigate the cognitive impairments of poor sleep quality and sleep restriction, respectively. We evaluated whether acute exercise may offset sleep restriction's impairment of long-term declarative memory compared to average sleep alone. A total of 92 (82% females) healthy young adults (24.6 ± 4.2 years) were randomly allocated to one of four evening groups: sleep restriction only (S5, 5-6 h/night), average sleep only (S8, 8-9 h/night), high-intensity interval training (HIIT) before restricted sleep (HIITS5), or HIIT before average sleep (HIITS8). Groups either followed a 15-min remote HIIT video or rest period in the evening (7:00 p.m.) prior to encoding 80 face-name pairs. Participants completed an immediate retrieval task in the evening. The next morning a delayed retrieval task was given after their subjectively documented sleep opportunities. Long-term declarative memory performance was assessed with the discriminability index (d') during the recall tasks. While our results showed that the d' of S8 (0.58 ± 1.37) was not significantly different from those of HIITS5 (-0.03 ± 1.64, p = 0.176) and HIITS8 (-0.20 ± 1.28, p = 0.092), there was a difference in d' compared to S5 (-0.35 ± 1.64, p = 0.038) at the delayed retrieval. These results suggest that the acute evening HIIT partially reduced the detrimental effects of sleep restriction on long-term declarative memory.

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The discrepancies in the effects of napping on sleep quality may be due to differences in methodologies, napping behaviours, and daytime activity levels across studies. We determined whether napping behaviours and daytime activity levels are associated with night-time sleep fragmentation and sleep quality in young adults. A total of 62 healthy adults (mean [SD] age 23.5 [4.2] years) completed screening questionnaires for sleep habits, physical activity, medical and psychological history. Actigraphy was used to record sleep including naps. The fragmentation algorithm (KRA ) was applied to the actigraphic data to measure night-time sleep fragmentation. We classified participants' nap frequency as "non-nappers" (0 naps/8 days), "moderate nappers" (1-2 naps/8 days) or "frequent nappers" (≥3 naps/8 days) naps. Nap duration was defined as "short" (≤60 min) or "long" (>60 min). Naps' proximity to the night sleep episode was defined as "early" (≥7 h) and "late" (<7 h) naps. Outcome variables were night-time KRA and actigraphic sleep variables. Frequent nappers had a significantly higher KRA than moderate nappers (p < 0.01) and non-nappers (p < 0.02). Late naps were associated with poorer measures of night sleep quality versus early naps (all p ≤ 0.02). Nap duration and daytime activity were not associated with significant differences in the outcome variables (all p > 0.05). KRA correlated with sleep duration, sleep efficiency, and awakenings (r = -0.32, -0.32, and 0.53, respectively; all p < 0.05). Frequent napping and late naps may be associated with increased sleep fragmentation and poorer sleep quality, reflected in longer sleep onsets and increased awakenings. These findings have implications for public health sleep hygiene recommendations.

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Moderate-intensity exercise is generally recommended for improving sleep, whereas, high-intensity exercise (HIE) prior to bedtime is often discouraged. We conducted a systematic review and meta-analysis to determine if acute or regular (chronic) HIE performed before bedtime disrupts nighttime sleep of healthy adult, good sleepers compared with a no-exercise control. Six databases (PubMed, EMBASE, Scopus, Web of Science, CENTRAL, and PsycINFO) were searched from inception to 31st May, 2021. Studies were experimental trials published in English language, objectively (polysomnography, actigraphy) and/or subjectively assessed sleep after evening HIE in sedentary and physically fit, good sleepers (aged 18-50 y old). The revised Cochrane risk of bias tool for randomized trials was used to assess risk of bias in the included studies. The random-effects model was used for the meta-analyses. We included 15 acute evening HIE studies in the meta-analysis with a total of 194 participants. Acute evening HIE ending 0.5-4 h before bedtime decreased rapid eye movement sleep (-2.34%; p = 0.002) compared with a no-exercise control. No other significant sleep changes occurred. A regular evening HIE did not disrupt nighttime sleep. Overall, acute evening HIE performed 2-4 h before bedtime does not disrupt nighttime sleep of healthy, young and middle-aged adults. PROSPERO, protocol registration number: CRD42020218299.

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Sleep leads to the enhancement of memory, and physical exercise also improves memory along with beneficial effects on sleep quality. Potentially, sleep and exercise may operate independently upon memory; alternatively, they may operate synergistically to boost memory above and beyond exercise or sleep alone. We tested this hypothesis in 115 young healthy adults (23 ± 3.9 years) randomly allocated to one of the four conditions in a 2 (exercise vs. no exercise) × 2 (nap vs. no nap) design. The exercise intervention consisted of a 40-minute, moderate intensity cycling, while the no exercise condition was an equivalent period of rest. This was followed by a learning session in which participants memorized a set of 45 neutral pictures for a later test. Subsequently, participants were exposed to either a 60-minute sleep period (nap) or an equivalent time of resting wakefulness, followed by a visual recognition test. We found a significant interaction between the effects of exercise and nap (p = 0.014, η p2 = 0.053), without significant main effects of exercise or nap conditions. Participants who experienced both exercise plus nap were significantly more accurate (83.8 ± 2.9) than those who only napped (81.1 ± 5.4, p = 0.027) and those who only exercised (78.6 ± 10.3, p = 0.012). Within the combined nap plus exercise group, higher recognition accuracies were associated with higher sleep spindle densities (r = 0.46, p = 0.015). Our results demonstrate that short-term exercise and a nap improve recognition memory over a nap or exercise alone. Exercise and sleep are not independent factors operating separately upon memory but work together to enhance long-term memory.

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BACKGROUND: While cognitive-behavioral therapy for insomnia constitutes the first-line treatment for chronic insomnia, only few reports have investigated how sleep architecture relates to response to this treatment. In this pilot study, we aimed to determine whether pre-treatment sleep spindle density predicts treatment response to cognitive-behavioral therapy for insomnia. METHODS: Twenty-four participants with chronic primary insomnia participated in a 6-week cognitive-behavioral therapy for insomnia performed in groups of 4-6 participants. Treatment response was assessed using the Pittsburgh Sleep Quality Index and the Insomnia Severity Index measured at pre- and post-treatment, and at 3- and 12-months' follow-up assessments. Secondary outcome measures were extracted from sleep diaries over 7 days and overnight polysomnography, obtained at pre- and post-treatment. Spindle density during stage N2-N3 sleep was extracted from polysomnography at pre-treatment. Hierarchical linear modeling analysis assessed whether sleep spindle density predicted response to cognitive-behavioral therapy. RESULTS: After adjusting for age, sex, and education level, lower spindle density at pre-treatment predicted poorer response over the 12-month follow-up, as reflected by a smaller reduction in Pittsburgh Sleep Quality Index over time. Reduced spindle density also predicted lower improvements in sleep diary sleep efficiency and wake after sleep onset immediately after treatment. There were no significant associations between spindle density and changes in the Insomnia Severity Index or polysomnography variables over time. CONCLUSION: These preliminary results suggest that inter-individual differences in sleep spindle density in insomnia may represent an endogenous biomarker predicting responsiveness to cognitive-behavioral therapy. Insomnia with altered spindle activity might constitute an insomnia subtype characterized by a neurophysiological vulnerability to sleep disruption associated with impaired responsiveness to cognitive-behavioral therapy.

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Research indicates that habitual short sleepers show more rapid accumulation of slow-wave sleep at the beginning of the night. Enhancement in performance on declarative memory tasks has been associated with early NonREM sleep, consisting of the highest percentage of slow-wave sleep. Twenty-four subjects (eight short sleepers 7 but <9h, seven long >or=9h) were tested. Subjects were presented with unfamiliar face stimuli and asked to memorize them for a subsequent test. Following sleep, the subjects were presented with the 40 "old/studied" items intermixed with 40 new and asked to indicate the previously presented stimuli. Event-related potentials (ERPs) were analyzed to verify the existence of the "Old/New" effect, i.e. amplitude difference [in ERPs] between the old and new stimuli. ANOVA on the scores revealed a significant interaction between the stimuli and group. Post-hoc test on the studied items revealed more accurate responses in the short sleepers compared to the average and long sleepers. Strikingly, the long sleepers failed to show significant retention of the old/studied items, with their recognition of old faces not different from chance. Reaction time (RT) responses were faster for the old vs. the new items. Pearson correlation revealed a significant negative correlation between accuracy and sleep duration in the short sleepers. However, long and average sleepers showed a positive correlation between the two variables. ANOVA performed on the ERPs revealed main effects of stimuli and site, and no interactions involving the group factor. In conclusion, our data show that individual differences in recognition memory performance may be associated with differences in habitual sleep duration.

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This study examined the role of sleep on event-related potential (ERP) indicators of memory following sleep and wake. We expected a larger ERP effect due to a facilitory effect of sleep on memory. During the study session, subjects memorized a series of stimuli (faces). At test, after a retention interval characterized by either sleep or by normal waking activities, subjects were asked to recognize old items intermixed with new. Results revealed differences in the old/new effect whereby the amplitude between old/new items was larger after sleep versus wake, suggesting a role of sleep in consolidation. Retention over sleep versus wake was associated with modified early and late frontal and posterior components possibly manifesting reduced interference inhibition, increased contextual processing, and facilitation of episodic memory. These findings suggest that ERP indices are differentially affected by sleep, reflecting differences in memory processing.

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STUDY OBJECTIVES: To verify that the classic "Old/New" memory effect can be detected after a long delay, and to investigate the differential influence of declarative memory processes after normal sleep and daytime wake. DESIGN: The protocol is a variation of a more traditional study-recognition test used in event-related potential (ERP) studies in which sleep or wake is inserted between the learning and recognition session in order to verify the existence of the Old/New effect (ie, positive shift that occurs when stimuli are repeated). ERPs were recorded during the recognition-test session. The protocol was based on early work that compared the effect of sleep on memory without recording sleep. SETTING: Data collection occurred in the outpatient sleep laboratory. PATIENTS OR PARTICIPANTS: Results from 13 subjects (6 men) aged between 21 and 39 years. MEASUREMENTS AND RESULTS: The subjects performed the recognition memory test after sleep and daytime wake periods. More-accurate performance for the old (studied) stimuli occurred after the sleep session. Analysis of variance on correctly answered reaction times revealed a significant effect of condition (old/new) with no difference across session. A repeated-measure analysis revealed differences in "Old/New" effect, whereby the amplitude difference between the old and new items was larger after sleep than after wake. CONCLUSIONS: This effect of sleep was found in early frontal and later posterior ERP components, processes that represent strategic, contextual processing and facilitation of episodic memory. Memory representation was not different across sessions. These findings suggest that sleep and wake facilitate 2 components of memory unequally, ie, episodic recognition and memory representation functioning.

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This study investigated gender differences on memory processing using event-related potentials (ERPs). Behavioral data and ERPs were recorded in 16 males and 10 females during a recognition memory task for faces. The behavioral data results showed that females performed better than males. Gender differences on ERPs were evidenced over anterior locations and involve the modulation of two spatially and temporally distinct components. These results are in general accordance with the view that males and females differ in the cognitive strategies they use to process information. Specifically, they could differ in their abilities to maintain information over interference and in the processing of the intrinsic contextual attributes of items, respectively, associated with the modulation of two anterior components. These interpretations lend support to the view that processing in females entails more detailed elaboration of information content than in males. Processing in males is more likely driven by schemas or overall information theme.

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