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The beneficial influence of sleep on memory consolidation is well established; however, the mechanisms by which sleep can dynamically consolidate new memories into existing networks for the continued environmental adaptation of the individual are unclear. The role of sleep in complex associative memory is an emerging field and the literature has not yet been systematically reviewed. Here, we systematically review the published literature on the role of sleep in complex associative memory processing to determine (i) if there is reasonable published evidence to support an active role for sleep facilitating complex associative processes such rule and gist extraction and false memory; (ii) to determine which sleep physiological events and states impact these processes, and to quantify the strength of these relationships through meta-analysis. Twenty-seven studies in healthy adults were identified which combined indicate a moderate effect of sleep in facilitating associative memory as tested behaviourally. Studies which have measured sleep physiology have reported mixed findings. Significant associations between sleep electrophysiology and outcome appear to be based largely on mode of acquisition. We interpret these findings as supporting reactivation based models of associative processing.

We aimed to investigate the contributions of visual letter form and abstract letter identity to the time course of letter recognition, by manipulating the typeface (i.e. font) in which letters were presented. Twenty-six adult participants completed a modified one-back task, where letters where presented in easy-to-read typefaces ("fluent" letter stimuli) or difficult-to-read typefaces ("disfluent" letter stimuli). Task instructions necessitated that participant's focus on letter identity not visual letter form. Electroencephalography was collected and event-related potentials (ERPs) were calculated relative to letter stimuli. It was found that typeface affected both early-mid (N1 amplitude and P2-N2 amplitude and latency) and late processing (450-600ms), thereby including time points whereby it is theorised that abstract identity is extracted from visual letter form (that is, 300ms post-stimulus). Visual features of the letter therefore affect its processing well beyond the currently theorised point at which abstract information is extracted; which could be explained by a feedback loop between abstract letter representations and lower-level visual form processing units, which is not included in current cognitive reading models., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Childhood sleep disordered breathing (SDB) is characterized by an increased work of breathing, restless night sleep and excessive daytime sleepiness and has been associated with cognitive impairment, behavioral disturbances and early cardiovascular changes. Compared to normal controls, children with SDB have elevated arousal thresholds and their sleep EEG may elicit cortical activation associated with arousals but often too subtle to be visually scored. The aim of this study was to assess EEG complexity throughout the respiratory cycle based on symbolic dynamics in children with SDB (n=40) and matched healthy controls. EEG amplitude values were symbolized based on the quartiles of their distribution and words of length 3 were formed and classed into 4 types based on their patterns. Children with SDB showed less complex EEG dynamics in non-REM sleep that was unrelated to the respiratory phase. In REM sleep normal children showed a respiratory phase-related reduction in EEG variability during the expiratory phase compared to inspiration, which was not apparent in children with SDB. In conclusion, respiratory cycle related EEG dynamics are altered in children with SDB during REM sleep and indicate changes in cortical activity.

Background: Disturbed sleep is detrimental to child behavior; however, the precise means by which this association occurs is unclear. Sleep and resilience can theoretically share an underlying neural mechanism and therefore influence one another. However, the role of resilience in the association between sleep and behavior is not known. The associations between sleep, resilience, and problematic behavior in children and adolescents aged 7-18 years were investigated in this study., Methods: A correlational design was used to determine the relationships between total sleep problems, indices of resilience, and internalizing and externalizing behaviors., Results: Sleep problems and resiliency variables were strongly correlated, and further, sleep problems were found to be predictive of resiliency scores. Resiliency significantly mediated the relationship between increased sleep problems and both overall internalizing and externalizing behavior problems, and specifically, measures of depression and anxiety., Conclusion: Sleep impacted levels of resilience such that greater sleep disturbance reduced resilience and consequently increased problematic behavior, potentially predisposing individuals to psychopathology.

Upper airway obstruction during adulthood is associated with cardiovascular morbidity; cardiovascular consequences of childhood upper airway obstruction are less well established. This study aimed at investigating the effect of childhood upper airway obstruction on respiratory sinus arrhythmia as a measure of cardiac vagal modulation during night-time sleep. Overnight polysomnography was conducted in 40 healthy children (20 M; age: 7.5 ± 2.6 years; body mass index percentile: 60.7 ± 26.4%) and 40 children with upper airway obstruction (24 M; age: 7.5 ± 2.7 years; body mass index percentile: 65.8 ± 31.9%). We used the phase-averaging technique to compute respiratory sinus arrhythmia amplitude and phase delay. To study sleep stage effects and the effect of upper airway obstruction, respiratory sinus arrhythmia was measured during all artefact-free sleep episodes, and after exclusion of respiratory events. A significant increase in respiratory sinus arrhythmia amplitude and phase delay was observed during stage 4 sleep as compared with rapid eye movement sleep in both groups (amplitude: controls = 0.10 ± 0.03 versus 0.07 ± 0.02 s, P < 0.01, respectively, and upper airway obstruction = 0.07 ± 0.03 versus 0.05 ± 0.03 s, P < 0.05, respectively; phase delay: controls = 3.1 ± 0.1 versus 3.0 ± 0.1 rad, P < 0.05, respectively, and upper airway obstruction = 3.13 ± 0.04 versus 3.04 ± 0.08 rad, P < 0.01, respectively). A significant association between respiratory sinus arrhythmia and apnea/hypopnea index was observed during stage 2 sleep in children with upper airway obstruction. Compared with healthy controls, a significant decrease in respiratory sinus arrhythmia amplitude during stage 2 sleep was observed in children with upper airway obstruction (0.09 ± 0.03 versus 0.06 ± 0.03 s, P < 0.05). However, this difference was not apparent when respiratory events were excluded from analysis. Importantly, respiratory sinus arrhythmia showed a strong negative correlation with body mass index. In conclusion, night-time respiratory sinus arrhythmia in children is sleep stage dependent and normal during quiet sleep in children with relatively mild upper airway obstruction., (© 2013 European Sleep Research Society.)

Purpose: Problematic behavior is widely reported in children with sleep-disordered breathing (SDB). Daytime behavior is an important component in the evaluation of clinical history in SDB; however, there is a reliance on parental report alone, and it is unclear whether reports by teachers will aid diagnosis., Methods: We assessed sleep and behavior reported by both parents and teachers in 19 children with SDB and 27 non-snoring controls. All children were screened for prior diagnoses of other medical and/or behavior and learning disorders and underwent polysomnography and both parental and teacher assessment of behavior., Results: Both parents and teachers report greater problematic behavior in SDB children, predominantly of an internalizing nature. Despite this consistency and moderate correlation between informants, the agreement between parent and teacher reports of individual child behavior was poor when assessed using Bland-Altman plots., Conclusions: Clinicians should be mindful that the behavioral history of a child being evaluated for SDB may vary depending on whether parent or teacher report is being discussed as this may influence clinical decision making.

Sleep disordered breathing (SDB) is characterized by repeated episodes of central or obstructive apneas, disturbing respiratory patterns. The purpose of this study is to quantify respiratory variability associated with apneic/hypopneic events by computing respiratory parameters and thoraco-abdominal asynchrony (TAA) over sleep periods preceding the occurrence of obstructive events in children with SDB. One minute artifact-free epochs of ribcage (RC) and abdominal (AB) signals were extracted from the respiratory inductive plethysmograph (RIP) channel of the PSG prior to the onset of each obstruction. Breath-by-breath values of TAA were computed using a Hilbert transform based technique that measures the phase shift between the RC and AB signals. In addition, the following parameters were computed breath-by-breath from the RC signal: inspiratory time (Ti), expiratory time (Te), total time (Ttot), and the inspiratory duty cycle (DC=Ti/Ttot). Standard deviation of the parameters (SD&#95;TAA, SD&#95;Ti, SD&#95;Te, SD&#95;Ttot, SD&#95;DC) over each 1 min epoch were calculated and averaged over each subject with respect to sleep stage. For comparison, similar measures were computed from within quiet breathing periods of each subject. We found that breaths immediately before apnea/hypopneas were associated with a high degree of variability in respiratory timing and TAA. The proposed variability analysis of RIP signals may be useful for detecting acute epochs of respiratory instability in children with SDB.

Aim: Disruptions to sleep in childhood are associated with poor behaviour and deficits in academic performance and executive function. Although academic performance of indigenous children from remote communities in Australia is documented as well below that of non-indigenous children, the extent of sleep disruption and its contribution to academic performance among this population has not been assessed. This pilot study aimed to objectively assess the sleep of remote indigenous children and the association between sleep disruption and both academic performance and executive function., Method: Twenty-one children from a remote Australian indigenous community aged 6-13 years wore actigraphy for two consecutive nights, reported subjective sleepiness, and were objectively assessed for academic performance (Wechsler Individual Achievement Test, 2nd Edition) and executive function (NEuroloPSYcological Assessment-II)., Results: Results show marked reduction in sleep time, sleep fragmentation, academic performance and auditory attention compared with non-indigenous norms. Sleep duration was not associated with performance, possibly because of reduced sleep and performance observed across the entire group. Sleep fragmentation was associated with reduced reading and numerical skills (P < 0.05)., Conclusions: The sleep of indigenous children in remote communities is an important area of future inquiry, and our initial findings of poor sleep and an association between sleep disruption and academic performance may have important implications for intervention strategies aimed at 'closing the gap'. Further studies should assess a broader range of demographic, social and economic factors to better understand the associations reported here and guide future intervention., (© 2012 The Authors. Journal of Paediatrics and Child Health © 2012 Paediatrics and Child Health Division (Royal Australasian College of Physicians).)

We present a technique based on the Hilbert transform to quantify the thoraco-abdominal asynchrony (TAA) based on the phase shift between ribcage (RC) and abdomenal (AB) breathing signals acquired using respiratory inductive plethysmography (RIP). We employed this method to investigate RIP during overnight polysomnography (PSG) in 40 healthy children for analysis of their breathing patterns in various stages of sleep (ss 2, 3, 4 and REM) and in two common sleeping positions (supine and lateral). RIP signals free of respiratory or movement artifacts were segmented into 30 second epochs. Those epochs with maximum power in the quiet breathing frequency range and positional invariance throughout were included for further processing. TAA was calculated from corresponding RC and AB excursions. We found a statistically significant influence of sleep position on the level of TAA in all stages of non-REM sleep. In conclusion, the Hilbert transform provides a simple tool for the quantification of thoraco-abdominal asynchrony.

The aim of this paper was to study the effect of spontaneous arousals during night-time sleep on the interactions between R-R intervals and respiratory phases in healthy children. We collected overnight polysomnography data of 40 healthy children and investigated cardio-respiratory interaction before and after spontaneous arousals during stage 2 sleep using joint symbolic dynamics. The R-R time series were extracted from electrocardiograms (ECG) and respiratory phases were obtained from abdominal sensors using the Hilbert transform. Both the series were transformed into ternary symbol vectors based on the changes between two successive R-R intervals or respiratory phases, respectively. Subsequently, words of length '2' were formed and the correspondence between words of the two series was determined to quantify cardio-respiratory interaction for pre- and post-spontaneous arousal episodes. We observed a brief but significant shortening in R-R and respiratory intervals after arousal. There was also a significant short-term increase in cardio-respiratory interaction during the first 30-second post-arousal episode as compared to 30-second pre-arousal episode (7.5±3.4 vs. 5.2±3.7%, p&#60;0.0001, respectively). In conclusion, spontaneous arousals in healthy children during night-time sleep are associated with a temporal but significant increase in cardio-respiratory interaction.

The aim of this paper was to study interactions between R-R intervals and respiratory phases in healthy children during night-time sleep using a novel technique based on joint symbolic dynamics. We investigated overnight polysomnography data of 40 healthy children. The R-R time series were extracted from electrocardiograms (ECG) and respiratory phases were obtained from abdominal sensors using the Hilbert transform. Both the series were transformed into ternary symbol vectors based on the changes between two successive R-R intervals or respiratory phases, respectively. Subsequently, words of length '2' were formed and the correspondence between words of the two series for each sleep stage was determined to quantify cardio-respiratory interaction. We found a significantly higher percentage of similarity in the joint symbolic dynamics of R-R intervals and respiratory phases during slow-wave (SW) sleep compared to any other sleep stage. There was, however, no significant effect of age, gender or BMI on cardio-respiratory interaction. In conclusion, joint symbolic dynamics provides a novel efficient technique for the analysis of cardio-respiratory interaction.

Arousal from sleep is associated with transient and abrupt cardiorespiratory changes, and elevated arousals associated with sleep disorders may trigger adverse cardiovascular sequela. In this paper, we provide the first data in children on cardiorespiratory responses to cortical arousal. Heart rate and ventilatory responses to arousal from stage 2 and rapid eye movement (REM) sleep were investigated in 40 normal, healthy Caucasian children (age: 7.7 +/- 2.6 years; body mass index z-score: 0.30 +/- 0.8). All children underwent overnight polysomnography studies. Cortical arousals were scored according to standard criteria. Heart rate changes were assessed over 30 s, starting 15 s prior to cortical arousal onset. Breathing rates were quantified three breaths before and after arousal onset. Arousals from stage 2 as well as REM sleep resulted in an R-R interval shortening of about 15%, independent of age and gender. The R-R interval shortening initiated at least 3 s before the cortical arousal onset. The breathing interval immediately after cortical arousal onset was significantly shortened (P < 0.001). In conclusion, cortical arousals in children are associated with an increase in breathing rate and significant heart rate accelerations, which typically precede the cortical arousal onset.

An asymmetric Mannich reaction of phenylacetate thioesters and sulfonylimines using cinchona alkaloid-based amino (thio)urea catalysts is reported that employs proximity-assisted soft enolization. This approach to enolization is based on the cooperative action of a carbonyl-activating hydrogen bonding (thio)urea moiety and an amine base contained within a single catalytic entity to facilitate intracomplex deprotonation. Significantly, this allows thioesters over a range of acidity to react efficiently, thereby opening the door to the development of a general mode of enolization-based organocatalysis of monocarboxylic acid derivatives.

The proportion of children who are overweight or obese has risen steadily in recent decades and approaches a quarter of all children in Western countries. This global epidemic of excess weight and adiposity in humans is associated with increased morbidity and mortality, especially related to diabetes and poor cardiovascular health. It would appear that obesity is also generally accepted to be an important risk factor in the development of sleep disordered breathing (SDB), in children as well as adults. The article, "The prevalence, anatomical correlates and treatment of sleep-disordered breathing in obese children and adolescents", by Verhulst et al., also in this issue, reviews evidence supporting the view that obese children are at higher risk of developing SDB. We believe, however, that the available studies do not support a straightforward association of overweight or obesity with increased prevalence of SDB. Rather, the available data is clearly equivocal mainly due to methodological differences between the previous studies. This review nonetheless examines the factors which may modulate the relationship between overweight or obesity and prevalence of SDB, particularly ethnicity and age.

Chewing has been shown to alleviate feelings of sleepiness and improve cognitive performance during the day. This study investigated the effect of chewing on alertness and cognitive performance across one night without sleep as well as the possible mediating role of cardiac autonomic activity. Fourteen adults participated in a randomized, counterbalanced protocol employing a chewing, placebo and caffeine condition. Participants completed tasks assessing psychomotor vigilance, tracking, grammatical reasoning, alertness and sleepiness each hour across the night. All participants received either placebo or caffeine (200 mg), while the chewing condition also chewed on a tasteless and odorless substance for 15 min each hour. Heart rate (HR), root mean square of the successive differences in R-R intervals on the ECG (RMSSD), and preejection period (PEP) were simultaneously recorded. Alertness and cognitive performance amongst the chewing condition did not differ or were in fact worse when compared with placebo. Similarly, measures of HR and RMSSD remained the same between these two conditions; however, PEP was reduced in the later part of the night in the chewing condition compared with a relative increase for placebo. Caffeine led to improved speed and accuracy on cognitive tasks and increased alertness when compared with chewing. Relative increases in RMSSD and reductions in HR were demonstrated following caffeine; however, no change in PEP was seen. Strong associations between cardiac parasympathetic activity and complex cognitive tasks, as well as between subjective alertness and simpler cognitive tasks, suggest a differential process mediating complex versus simple cognitive performance during sleep deprivation.