Neurophysiological Basis of Sleep's Function on Memory and Cognition

Latent Default Mode Network Connectivity Patterns: Associations With Sleep Health and Adolescent Psychopathology

BACKGROUND

The present study examined default mode network (DMN) neural connectivity patterns among adolescents. Next, we tested two critical markers of sleep health-duration and efficiency, in predicting neural connectivity patterns. Last, we investigated the latent DMN profiles' predictive utility of internalizing and externalizing symptoms in youth.

METHODS

The study included 2811 youth (47.8% female; mean age = 11.94) enrolled in the Adolescent Brain Cognitive Development study. Sleep duration and efficiency were objectively measured via Fitbit wearable's (mean number of nights = 14.13). Latent profile analysis identified neural connectivity profiles within the DMN and between other networks (fronto-parietal, salience, ventral attention, and dorsal attention). Parents reported the youth's psychopathology symptoms.

RESULTS

Four DMN profiles were empirically identified: (1) moderate; (2) low within and high between; (3) high within and low between; and (4) high within and high between. Youth with shorter sleep duration were more likely to be classified as low within and high between subgroup. Youth with lower sleep efficiency were more likely to be classified as the high within and low between subgroup. There were between-group differences in externalizing problems one year later.

CONCLUSION

Our findings highlight unique neural patterns in youth and their associations with sleep and psychopathology. The results will inform clinical practice and preventive programming that attempts to address the crisis in youth mental health through a focus on mitigating sleep problems in youth.

Mapping Voice Assessment Procedures and Results in Individuals with Sleep-Related Breathing Disorder: A Scoping Review

OBJECTIVE

To map the procedures and characterize the results of multidimensional voice assessment of individuals with sleep-related breathing disorders.

METHOD

This scoping review searched the MEDLINE, LILACS, Scopus, EMBASE, Web of Science, Cochrane Central Register of Controlled Trials, ProQuest, and MedRxiv databases, manually searched citations, grey literature, and consulted with experts. It included studies whose participants had sleep-related breathing disorders and underwent voice assessment. Two calibrated reviewers independently searched, selected, and extracted data on publication, sample, and assessment; disagreements were resolved by consensus. The data were analyzed descriptively.

RESULTS

The search found 1089 studies, of which 32 were selected. The sample comprised one study on catathrenia and 31 on obstructive sleep apnea. Acoustic analysis was the most used voice assessment procedure for sleep-related breathing disorders. The most frequent measures and instruments were jitter and fundamental frequency in acoustic analysis; maximum phonation time in aerodynamic assessment; GRBAS in auditory-perceptual judgment; Vocal Handicap Index-10 in vocal self-assessment; and videolaryngostroboscopy in laryngeal imaging. Shimmer and jitter were the measures most used to distinguish individuals with and without sleep-related breathing disorders and most verified as abnormal in individuals affected by such conditions.

CONCLUSION

Obstructive sleep apnea is the most studied sleep-related breathing disorder in the voice clinic. Acoustic analysis was the most used method to assess sleep-related breathing disorders, with disturbance measures being the most altered, and the most used to differentiate individuals with and without sleep-related breathing disorders.

Sleep benefits perceptual but not movement-based learning of locomotor sequences

Practicing complex locomotor skills, such as those involving a step sequence engages distinct perceptual and motor mechanisms that support the recall of learning under new conditions (i.e., skill transfer). While sleep has been shown to enhance learning of sequences of fine movements (i.e., sleep-dependent consolidation), here we examined whether this benefit extends to learning of a locomotor pattern. Specifically, we tested the perceptual and motor learning of a locomotor sequence following sleep compared to wake. We hypothesized that post-practice sleep would increase locomotor sequence learning in the perceptual, but not in the motor domain. In this study, healthy young adult participants (n = 48; 18-33 years) practiced a step length sequence on a treadmill cued by visual stimuli displayed on a screen during training. Participants were then tested in a perceptual condition (backward walking with the same visual stimuli), or a motor condition (forward walking but with an inverted screen). Skill was assessed immediately, and again after a 12-h delay following overnight sleep or daytime wake (n = 12 for each interval/condition). Off-line learning improved following sleep compared to wake, but only for the perceptual condition. Our results suggest that perceptual and motor sequence learning are processed separately after locomotor training, and further points to a benefit of sleep that is rooted in the perceptual as opposed to the motor aspects of motor learning.

The effects of nonpharmacological sleep hygiene on sleep quality in nonelderly individuals: A systematic review and network meta-analysis of randomized controlled trials

The prevalence of locomotive syndrome naturally increases with age, but approximately half of nonelderly individuals also meet the criteria for locomotive syndrome, suggesting that even younger people need to pay attention to their own health status. Sleep is important for physical, cognitive, and psychological health. Some individuals with poor sleep quality may be at risk of developing negative health status. Although the effects of sleep hygiene strategies for elderly individuals have been well investigated, optimal nonpharmacological sleep hygiene strategies for improving sleep quality in nonelderly individuals has not been identified. We conducted a systematic review and network meta-analysis (NMA) of randomized controlled trials aimed to elucidate the effects of various nonpharmacological interventions on sleep quality in nonelderly individuals and to identify the optimal intervention. Cochrane Central Register of Controlled Trials, Medline, Cumulative Index to Nursing and Allied Health Literature, Physiotherapy Evidence Database, and Scopus were comprehensively searched. We identified 27 studies focusing on the effects of various nonpharmacological sleep hygiene strategies in nonelderly individuals, and 24 studies were applied into NMA. The present results showed that resistance training was the most effective intervention for improving sleep quality in nonelderly individuals. In addition, this study revealed the effects of nonpharmacological interventions, such as physical activity, nutritional intervention, as well as exercise interventions. This is the first report that utilized NMA to compare the effects of various nonpharmacological interventions on sleep quality in nonelderly individuals.

Temporal Associations between Actigraphy-Measured Daytime Movement Behaviors and Nap Sleep in Early Childhood

The purpose of this micro-longitudinal study was to explore daily associations between daytime movement behaviors (sedentary time and physical activity) and nap sleep in young children. In 298 children (age = 51.0 ± 9.6 months, 43.6% female), wrist-based actigraphy (mean wear time = 10 days) assessed sedentary time, total physical activity, and provided an estimate of nap sleep duration and efficiency. Multilevel logistic and linear regression models were used to examine temporal within-person relations between wake behaviors and nap sleep, and adjusted for overnight sleep duration between days of interest, age, sex, and socioeconomic status. Movement behaviors were not related to the likelihood of next-day napping, but when children were less sedentary (OR = 0.96; p < 0.001) or more active (OR = 1.01; p = 0.001) in the morning, they were more likely to nap that same day. Movement behaviors were not associated with nap sleep duration or efficiency. Conversely, on days children napped, they were less sedentary (B = -2.09, p < 0.001) and more active (B = 25.8, p < 0.001) the following day. Though napping and movement behaviors had some reciprocal relations, effect sizes in the present study were small. Further studies should examine children with more diverse sleep health and from different childcare settings.

Recurrent Hippocampo-neocortical sleep-state divergence in humans

Sleep is assumed to be a unitary, global state in humans and most other animals that is coordinated by executive centers in the brain stem, hypothalamus, and basal forebrain. However, the common observation of unihemispheric sleep in birds and marine mammals, as well as the recently discovered nonpathological regional sleep in rodents, calls into question whether the whole human brain might also typically exhibit different states between brain areas at the same time. We analyzed sleep states independently from simultaneously recorded hippocampal depth electrodes and cortical scalp electrodes in eight human subjects who were implanted with depth electrodes for pharmacologically intractable epilepsy evaluation. We found that the neocortex and hippocampus could be in nonsimultaneous states, on average, one-third of the night and that the hippocampus often led in asynchronous state transitions. Nonsimultaneous bout lengths varied from 30 s to over 30 min. These results call into question the conclusions of studies, across phylogeny, that measure only surface cortical state but seek to assess the functions and drivers of sleep states throughout the brain.

Age-related heterogeneity revealed by disruption of white matter structural networks in patients with first-episode untreated major depressive disorder: WM Network In OA-MDD

The clinical treatment and prognosis of major depressive disorder (MDD) are limited by the high degree of disease heterogeneity. It is unclear whether there is a potential network mechanism for age-related heterogeneity. We aimed to uncover the heterogeneity of the white matter (WM) network at different ages of onset and its correlation with different symptom characteristics. 85 first-episode MDD patients and 84 corresponding healthy controls (HCs) were recruited and underwent diffusion tensor imaging scans. Structural network characteristics were analyzed using graph theory methods. We observed an accelerated age-related decline of the WM network in MDD patients compared with HCs. Distinct symptom-related networks were identified in three MDD groups with different onset-age. For early-onset MDD (18-29 years; EOD), higher guilt and loss of interest were correlated with the insula, and inferior parietal lobe which in default mode network and salience network. For mid-term-onset MDD (30-44 years; MOD), higher somatic symptoms were correlated with thalamus which in cortico-striatal-thalamic-cortical circuit. For later-onset MDD (45-60 years; LOD), poor sleep symptoms were correlated with the caudate in the basal ganglia, which suggests the cingulate operculum network in the control of sleep. These results supported a circuit-based heterogeneity associated with the age of onset in MDD. Understanding this circuit-based heterogeneity might help to develop a new target for clinical treatment strategies.

Age-related changes in sleep-dependent novel word consolidation

Learning new words is a vital, life-long process that benefits from memory consolidation during sleep in young adults. In aging populations, promoting vocabulary learning is an attractive strategy to improve quality of life and workplace longevity by improving the integration of new technology and the associated terminology. Decreases in sleep quality and quantity with aging may diminish sleep-dependent memory consolidation for word learning. Alternatively, given that older adults outperform young adults on vocabulary-based tasks, and that strength of memory encoding (how well older adults learn) predicts sleep-dependent memory consolidation, word learning may uniquely benefit from sleep in older adults. We assessed age-related changes in memory for novel English word-definition pairs recalled following intervals spent asleep and awake. While sleep was shown to fully preserve memory for word/definition pairs in young adults (N = 53, asleep = 32, awake = 21, 18-30 years), older adults (N = 45, asleep = 21, awake = 24, 58-75 years) forgot items equally over wake and sleep intervals but preserved the accuracy of typed responses better following sleep. However, this was modulated by the strength of encoded memories: the proportion of high strength items consolidated increased for older adults following sleep compared to wake. Older adults consolidated a lower proportion of medium strength items across both sleep and wake intervals compared to young adults. Our results contribute to growing evidence that encoding strength is crucially important to understand the expression of sleep-dependent benefits in older adults and assert the need for sufficiently sensitive performance metrics in aging research.

Walk to a better night of sleep: testing the relationship between physical activity and sleep

OBJECTIVES

Many do not sleep well, particularly middle-aged and older adults. Physical activity (PA) shows promise for improving sleep; however, populations with clinical sleep disturbances have been a research focus. It remains unclear whether low-impact daily PA, like walking, can affect sleep in healthy adults.

DESIGN

The current study was embedded within a 4-week randomized controlled trial to increase PA.

SETTING

Participants from the greater Boston area were recruited to participate in a 4-week walking intervention on a rolling basis between October 2015 and August 2016.

PARTICIPANTS

Fifty-nine participants (72% female) were enrolled in the study, with an average age of 49.43 (±8.40) years.

INTERVENTION

The 4-week intervention was aimed at increasing participants' daily steps as the primary outcome. The current, supplementary study examined relationships between monthly and daily PA and sleep.

MEASUREMENTS

Steps and active minutes were measured daily using a Fitbit Zip. Self-reports of sleep quality and duration were assessed daily, along with before and after the intervention.

RESULTS AND CONCLUSIONS

Averaged across the month, daily active minutes were positively related to sleep quality but not duration. Sex moderated this relationship; women who took more steps and were more active reported sleeping better than those less active. Within persons, on days that participants were more active than average, they reported better sleep quality and duration in both sexes. Results suggest that low-impact PA is positively related to sleep, more so in women than men. Findings also showed that PA plays a greater role in predicting sleep quality than duration.

Novel word learning in older adults: A role for sleep?

Sleep is an offline period during which newly acquired semantic information is transformed into longer-lasting memories. Language acquisition, which requires new word learning and semantic integration, is preferentially benefitted by a period of sleep in children and young adults. Specific features of sleep (e.g., sleep stage characteristics) have been associated with enhanced language acquisition and generalization. However, with increasing age, even in healthy individuals, sleep quality and quantity decrease. Simultaneously, deficits in word retrieval and new word learning emerge. Yet it is unknown whether age-related alterations in language ability are linked with alterations in sleep. The goal of this review is to examine changes in language learning and sleep across the lifespan. We consider how sleep detriments that occur with aging could affect abilities to learn novel words and semantic generalization and propose hypotheses to motivate future research in this area.

Emotional bias of sleep-dependent processing shifts from negative to positive with aging

Age-related memory decline has been proposed to result partially from impairments in memory consolidation over sleep. However, such decline may reflect a shift toward selective processing of positive information with age rather than impaired sleep-related mechanisms. In the present study, young and older adults viewed negative and neutral pictures or positive and neutral pictures and underwent a recognition test after sleep or wake. Subjective emotional reactivity and affect were also measured. Compared with waking, sleep preserved valence ratings and memory for positive but not negative pictures in older adults and negative but not positive pictures in young adults. In older adults, memory for positive pictures was associated with slow wave sleep. Furthermore, slow wave sleep predicted positive affect in older adults but was inversely related to positive affect in young adults. These relationships were strongest for older adults with high memory for positive pictures and young adults with high memory for negative pictures. Collectively, these results indicate preserved but selective sleep-dependent memory processing with healthy aging that may be biased to enhance emotional well-being.

Declarative and Non-declarative Memory Consolidation in Children with Sleep Disorder

Healthy sleep is essential in children’s cognitive, behavioral, and emotional development. However, remarkably little is known about the influence of sleep disorders on different memory processes in childhood. Such data could give us a deeper insight into the effect of sleep on the developing brain and memory functions and how the relationship between sleep and memory changes from childhood to adulthood. In the present study we examined the effect of sleep disorder on declarative and non-declarative memory consolidation by testing children with sleep-disordered breathing (SDB) which is characterized by disrupted sleep structure. We used a story recall task to measure declarative memory and Alternating Serial Reaction time (ASRT) task to assess non-declarative memory. This task enables us to measure two aspects of non-declarative memory, namely general motor skill learning and sequence-specific learning. There were two sessions: a learning phase and a testing phase, separated by a 12 h offline period with sleep. Our data showed that children with SDB exhibited a generally lower declarative memory performance both in the learning and testing phase; however, both the SDB and control groups exhibited retention of the previously recalled items after the offline period. Here we showed intact non-declarative consolidation in SDB group in both sequence-specific and general motor skill. These findings suggest that sleep disorders in childhood have a differential effect on different memory processes (online vs. offline) and give us insight into how sleep disturbances affects developing brain.

Sleep and anxiety in late childhood and early adolescence

PURPOSE OF REVIEW

Adolescence is a period of dynamic change in both sleep and emotional systems, with related increases in problems controlling emotion and behavior. Youth with anxiety enter adolescence with pre-existing vulnerabilities in systems of sleep and emotion that may place them at heightened risk. This review summarizes recent research on sleep and anxiety during the transition to adolescence, and highlights emerging themes.

RECENT FINDINGS

Prospective studies support that sleep predicts anxiety symptoms in early adolescence. Notably, robust evidence for subjective sleep problems in anxious youth is not well corroborated by objective assessments. Longitudinal designs and methodology that carefully examine dimensions of anxiety and sleep may clarify inconsistencies. Preliminary evidence suggests that late childhood to early adolescence may be a sensitive period for escalating problems with sleep and anxiety. Recent advances in the neuroscience of sleep can further refine integrative mechanistic models of developmental psychopathology - the role of sleep in emotional learning and memory is provided as an example.

SUMMARY

Sleep problems are common and prospectively predict escalating anxiety symptoms. Precision is needed regarding the nature of sleep disruption, and how and when sleep affects various aspects of developmental trajectories. This precision, along with advances in the neuroscience of sleep, may lead to developmentally informed translational interventions.

Sleep protects memories from interference in older adults

In a recent study, we demonstrated that sleep-dependent consolidation of declarative memories is preserved in older adults. The present study examined whether this benefit of sleep for declarative learning in older adults reflects a passive role of sleep in protecting memories from decay or an active role in stabilizing them. Young and older adults learned a visuospatial task, and recall was probed after sleep or wake. Although a reduction in performance was observed after sleep and wake, task-related interference before recall had a larger detriment on performance in the wake condition. This was true for young and high performing older adults only. Low performing older adults did not receive a benefit of sleep on the visuospatial task. Performance changes were associated with early night nonrapid eye movement sleep in young adults and with early night rapid eye movement sleep in high performing older adults. These results demonstrate that performance benefits from sleep in older adults as a result of an active memory stabilization process; importantly, the extent of this benefit of sleep is closely linked to the level of initial acquisition of the episodic information in older adults.

Consolidation of novel word learning in native English-speaking adults

Sleep has been shown to improve the retention of newly learned words. However, most methodologies have used artificial or foreign language stimuli, with learning limited to word/novel word or word/image pairs. Such stimuli differ from many word-learning scenarios in which definition strings are learned with novel words. Thus, we examined sleep's benefit on learning new words within a native language by using very low-frequency words. Participants learned 45 low-frequency English words and, at subsequent recall, attempted to recall the words when given the corresponding definitions. Participants either learned in the morning with recall in the evening (wake group), or learned in the evening with recall the following morning (sleep group). Performance change across the delay was significantly better in the sleep than the wake group. Additionally, the Levenshtein distance, a measure of correctness of the typed word compared with the target word, became significantly worse following wake, whereas sleep protected correctness of recall. Polysomnographic data from a subsample of participants suggested that rapid eye movement (REM) sleep may be particularly important for this benefit. These results lend further support for sleep's function on semantic learning even for word/definition pairs within a native language.

The effects of sleep dysfunction on cognition, affect, and quality of life in individuals with cerebellar ataxia

STUDY OBJECTIVE

Cerebellar ataxia comprises a group of debilitating diseases that are the result of progressive cerebellar degeneration. Recent studies suggest that, like other neurodegenerative diseases, sleep impairments are common in cerebellar ataxia. In light of the role of sleep in mood regulation and cognition, we sought to assess interactions between sleep, cognition, and affect in individuals with cerebellar ataxia.

METHODS

A survey of 176 individuals with cerebellar ataxia was conducted. The battery of instruments included a modified International Cooperative Ataxia Rating Scale, Pittsburgh Sleep Quality Index, Restless Leg Syndrome Questionnaire, REM Behavior Disorder Questionnaire, Beck Depression Inventory, Epworth Sleepiness Scale, and a Composite Cognitive Questionnaire.

RESULTS

Fifty-one percent of individuals indicated significant sleep disturbances on the Pittsburgh Sleep Quality Index, 73% of participants had two or more symptoms of restless leg syndrome, and 88% had two or more symptoms of REM behavior disorder. Ataxia severity, based on the modified International Cooperative Ataxia Rating Scale, predicted scores on the Pittsburgh Sleep Quality Index, the Epworth Sleepiness Scale and REM Behavior Disorder Questionnaire. Median split analyses revealed that cognitive function appeared to be reduced and depressive symptoms were greater for those individuals with poor subjective sleep quality and severe RLS. Importantly, sleep appears to play a mediatory role between disease severity and depressive symptoms.

CONCLUSIONS

These results suggest that disturbed sleep may have detrimental effects on cognition and affect in individuals with cerebellar ataxia. While objective measures are needed, such results suggest that treating sleep deficits in these individuals may improve cognitive and mental health as well as overall quality of life.

Sleep-dependent consolidation of value-based learning

It has been suggested that sleep selectively enhances memories with future relevance. Given that sleep's benefits can vary by item within a learning context, the present study investigated whether the amount of sleep-dependent consolidation may vary across items based on the value of the to-be-learned material. For this purpose, we used a value-based learning paradigm in which participants studied words paired with point values. There were two groups; participants either studied the words in the evening and were tested after a 12 hr interval containing a full night of sleep, or studied the words in the morning and were tested after 12 hr of continuous daytime wake. Free recall (F(1,36) = 19.35, p<.001) and recognition accuracy (F(1,36) = 7.59, p = .01) for words were better following sleep relative to wake. However there was no difference in the linear increase in the probability of delayed recall with increasing word value for sleep and wake groups (p = .74). Thus, while encoding may vary with the value of the to-be-learned item, sleep-dependent consolidation does not.