Frontal lobe function, sleep loss and fragmented sleep

Sleep measures expressing 'functional uncertainty' in elderlies' sleep

BACKGROUND

The notion of 'functional uncertainty' during sleep was first proposed to indicate an inability of the central nervous system to maintain stable states by coordinating physiological processes. While the presence of functional uncertainty phenomena has been shown in infants and hypothesized in the elderly, its actual occurrence in the aged population has never been systematically investigated.

OBJECTIVE

The aim of the study is to identify, in the sleep of aged individuals, indexes of sleep instability and fragmentation as markers of functional uncertainty, by comparing a sample of healthy elderly subjects to one of young adults.

METHODS

We compared polysomnograhic recordings of 20 healthy elderly subjects (age range 65-85 years) with those of 20 young individuals (age range 22-32 years), with special regard to the variables expressing functional uncertainty in sleep, such as continuity (e.g. arousals, awakenings), stability (e.g. state transitions, periods of marked 'functional uncertainty') and cyclic organization parameters.

RESULTS

Significant differences emerged for all variables of interest: the elderly group showed higher indexes of fragmentation and instability than the young, as well as less and shorter cycles, and a lower percentage of time spent in cycles.

CONCLUSION

Our results support the hypothesis of a progressive sleep quality disruption with aging, expressed by pronounced sleep instability, fragmentation and disorganization. We propose that functional uncertainty measures could usefully be included in standard sleep assessments on both aged and sleep-disordered populations as accurate sleep quality indexes.

Sleep loss, circadian mismatch, and abnormalities in reorienting of attention in night workers with shift work disorder

STUDY OBJECTIVES

Permanent night-shift workers may develop shift-work disorder (SWD). In the current study, we evaluated neurophysiological and behavioral indices of distractibility across times prior to the night shift (T1), during night hours (T2), and after acute sleep deprivation (T3) in permanent hospital night workers with and without SWD.

METHODS

Ten asymptomatic night workers (NW) and 18 NW with SWD participated in a 25-h sleep deprivation study. Circadian phase was evaluated by dim-light salivary melatonin onset (DLMO). Objective sleepiness was evaluated using the Multiple Sleep Latency Test (MSLT). Electrophysiological distractibility was evaluated by brain event-related potentials (ERP), whereas behavioral distractibility was evaluated by performance on a visual task in an auditory-visual distraction paradigm.

STATISTICAL ANALYSES

Comparisons of ERP results were performed by repeated-measures analysis of variance, and t-tests were used where appropriate. A Mann-Whitney U test was used for comparison of variables (MLST, Stanford Sleepiness Scale, and DLMO) that deviated from normal.

RESULTS

First, in the SWD group, the reorienting negativity ERP amplitude was significantly attenuated compared to that in the NW group. Second, the SWD group had shorter MSLT during night shift hours (4.8 ± 4.9 min) compared to that in NW (7.8 ± 3.7 min; U = 47; z = -2.1; P < 0.03). Third, NW with SWD had a DLMO at 20:27 ± 5.0 h, whereas healthy NW had a DLMO at 05:00 ± 3.4 h (U = 43.5; z = -2.22, P < 0.03). Finally, acute sleep deprivation impaired behavioral performance and the P3a ERP in both groups.

CONCLUSIONS

Our results demonstrate specific deficits in neurophysiological activity in the attentional domain among the shift-work disorder group relative to night workers.

Screening for sleep apnoea in mild cognitive impairment: the utility of the multivariable apnoea prediction index

Purpose. Mild cognitive impairment (MCI) is considered an “at risk” state for dementia and efforts are needed to target modifiable risk factors, of which Obstructive sleep apnoea (OSA) is one. This study aims to evaluate the predictive utility of the multivariate apnoea prediction index (MAPI), a patient self-report survey, to assess OSA in MCI. Methods. Thirty-seven participants with MCI and 37 age-matched controls completed the MAPI and underwent polysomnography (PSG). Correlations were used to compare the MAPI and PSG measures including oxygen desaturation index and apnoea-hypopnoea index (AHI). Receiver-operating characteristics (ROC) curve analyses were performed using various cut-off scores for apnoea severity. Results. In controls, there was a significant moderate correlation between higher MAPI scores and more severe apnoea (AHI: r = 0.47, P = 0.017). However, this relationship was not significant in the MCI sample. ROC curve analysis indicated much lower area under the curve (AUC) in the MCI sample compared to the controls across all AHI severity cut-off scores. Conclusions. In older people, the MAPI moderately correlates with AHI severity but only in those who are cognitively intact. Development of further screening tools is required in order to accurately screen for OSA in MCI.

The effects of poor sleep quality on cognitive function of patients with cirrhosis

OBJECTIVES

This study was conducted to assess the ill-defined relationship between sleep quality and multiple, specific domains of cognitive function in patients with cirrhosis.

METHODS

A comprehensive battery of neuropsychological tests (divided into six neurocognitive domains) and a standardized, validated measure of sleep quality (Pittsburgh Sleep Quality Index [PSQI]) were administered to patients with cirrhosis and without evidence of overt hepatic encephalopathy, recruited from liver transplant and advanced liver disease clinics (n = 34). An inflammatory bowel disease (IBD) control group (n = 23) was similarly recruited and evaluated to control for the secondary effect of a chronic illness on cognition. PSQI global and component scores were used to predict cognitive function in each neurocognitive domain, using linear regression.

RESULTS

Global PSQI scores were significantly higher (indicating poorer sleep quality) in the cirrhosis group (median [range] = 10 [1-19]) than in IBD controls = 5 (1-14); p = 0.002). After controlling for age and education, short duration of sleep was associated with impaired memory for patients with cirrhosis; the use of soporific agents was associated with poor visual-perceptual function in patients with IBD.

CONCLUSIONS

Poor sleep was associated with worsening of the already impaired cognitive function of patients with cirrhosis.

Sleep and cognitive problems in patients with attention-deficit hyperactivity disorder

OBJECTIVES

Attention-deficit hyperactivity disorder (ADHD) is characterized by inattentive and impulsive behavior. Many ADHD patients reportedly have cognitive dysfunction and sleep problems, including longer sleep latency, lower sleep efficiency, and shorter total sleep time. The purpose of this study was to examine neurocognitive functions and nocturnal sleep parameters in patients with ADHD, using a cognitive function test and actigraphy.

METHODS

Subjects included 37 male patients with ADHD and 32 controls (7-12 years of age). For each participant, we determined intelligence quotient (IQ) and administered the Matching Familiar Figures Test (MFFT) and 72-hour actigraphy. The relationships between sleep parameters and cognitive functions were assessed.

RESULTS

ADHD patients significantly differed from controls in several cognitive functions and sleep variables. In the MFFT, response error rate (P<0.001) and error counts (P=0.003) were significantly increased in ADHD patients compared with control children. MFFT response latency was significantly shorter in ADHD patients than in controls (P<0.001). In addition, sleep latency (P=0.01), wake after sleep onset (WASO) (P<0.001), and fragmentation index (P<0.001) were evaluated by actigraphy and found to be significantly increased in patients with ADHD compared with controls. However, no significant differences in total sleep time or sleep efficiency were observed. WASO and response error rates were positively correlated in patients with ADHD (rho =0.52, P=0.012). Furthermore, fragmentation index sleep variables were significantly positively correlated with response error (rho =0.44, P=0.008) and response latency rates (rho =0.4, P=0.018) in the MFFT. Reaction error rate was significantly associated with the fragmentation index (beta =0.94, P=0.024).

CONCLUSION

Patients with ADHD had more sleep problems, including significantly increased sleep latency, WASO, and fragmentation index, and poorer cognitive function, compared with controls. Some of these sleep problems, including WASO and the fragmentation index, were positively correlated with impulsivity, illustrated by the cognitive function tests in patients with ADHD. However, further studies with large sample sizes and the addition of polysomnography and determination of ADHD subtypes should be performed to confirm our results regarding sleep and cognitive problems in patients with ADHD.

Evaluating sleep and cognition in HIV

OBJECTIVE

To examine the relationship between measures of sleep quality and cognitive performance in HIV-positive individuals stable on combination antiretroviral therapy.

DESIGN

Multimethod assessments of sleep quality, patterns, and cognitive performance were assessed in a predominantly black HIV-positive cohort.

METHODS

Sleep quality and patterns were characterized in 36 subjects by polysomnogram, 2-week actigraphy monitoring, and validated sleep questionnaires. Cognitive performance was assessed with a battery of neuropsychological tests.

RESULTS

The majority of participants were cognitively impaired [based on Frascati (75%) criteria]. Self-reported mean scores on the Pittsburgh sleep quality index and the insomnia severity scale suggested poor sleep quality. Better cognitive performance, particularly on tasks of attention, frontal/executive function, and psychomotor/motor speed, was associated with polysomnogram sleep indices (ie, reduced wake after sleep onset, greater sleep efficiency, greater sleep latency, and greater total sleep time). Thirty-seven percent of participants had sleep patterns suggestive of chronic partial sleep deprivation, which was associated with significantly worse performance on the digit symbol test (P = 0.006), nondominant pegboard (P = 0.043), and verbal fluency tests (P = 0.044).

CONCLUSIONS

Our results suggest that compromised sleep quality and duration may have a significant impact on cognitive performance in HIV-positive individuals. Future studies are warranted to determine the utility of sleep quality and quantity indices as potential predictive biomarkers for development and progression of future HIV-associated neurocognitive disorder.

Daytime sleepiness is associated with decreased default mode network connectivity in both young and cognitively intact elderly subjects

STUDY OBJECTIVES

Sleep deprivation and daytime somnolence impair numerous aspects of physical, cognitive, and memory performance. However, most studies examining the effect of somnolence on brain function focus on acute sleep restriction in young adults. We examine the relationship between chronic daytime somnolence and connectivity in six brain networks in both young and elderly subjects using stimulus-free resting-state functional magnetic resonance imaging.

DESIGN

Cross-sectional.

SETTING

Outpatient research at the Massachusetts General Hospital.

PARTICIPANTS

Young (n = 27) and elderly (n = 84) healthy, cognitively normal volunteers.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Compared with young subjects, cognitively normal elderly adults report less daytime somnolence on the Epworth Sleepiness Scale (ESS) (P = 0.019) and display reduced default mode network (DMN) connectivity (P = 0.004). Across all subjects, increasing daytime sleepiness was associated with decreasing functional connectivity in the DMN (P = 0.003, partial r of ESS = -0.29). There was no difference in the slope of this relationship between young adults and elderly subjects. No other cortical networks were correlated with daytime sleepiness. Daytime sleepiness and DMN connectivity were not related to sex, brain structure, or body mass index.

CONCLUSIONS

These findings suggest that daytime sleepiness is associated with impaired connectivity of the DMN in a manner that is distinct from the effects of aging. This association is important to consider in any study using DMN connectivity as a biomarker. Additionally, these results may help identify those subjects at risk for future memory decline.

Nocturnal awakening and sleep efficiency estimation using unobtrusively measured ballistocardiogram

Fragmented sleep due to frequent awakenings represents a major cause of impaired daytime performance and adverse health outcomes. Currently, the gold standard for studying and assessing sleep fragmentation is polysomnography (PSG). Here, we propose an alternative method for real-time detection of nocturnal awakening via ballistocardiography using an unobtrusive polyvinylidene fluoride (PVDF) film sensor on a bed mattress. From ballistocardiogram, heart rate and body movement information were extracted to develop an algorithm for classifying sleeping and awakening epochs. In total, ten normal subjects (mean age 38.7 ± 14.6 years) and ten patients with obstructive sleep apnea (OSA) (mean age 44.2 ± 16.5 years) of varying symptom severity participated in this study. Our study detected awakening epochs with an average sensitivity of 85.3% and 85.2%, specificity of 98.4% and 97.7%, accuracy of 97.4% and 96.5%, and Cohen's kappa coefficient of 0.83 and 0.81 for normal subjects and OSA patients, respectively. Also, sleep efficiency was estimated using detected awakening epochs and then compared with PSG results. Mean absolute errors in sleep efficiency were 1.08% and 1.44% for normal subjects and OSA patients, respectively. The results presented here indicate that our suggested method could be reliably applied to real-time nocturnal awakening detection and sleep efficiency estimation. Furthermore, our method may ultimately be an effective tool for long-term, home monitoring of sleep-wake behavior.

Sleep disorder in childhood impairs declarative but not nondeclarative forms of learning

A large amount of studies have investigated the association between sleep and memory systems. However, remarkably little is known of the effect of sleep disorders on declarative and nondeclarative memory for children. In the present study we examined the effects of sleep disorders on different aspects of memory functions by testing children with sleep-disordered breathing (SDB), which is characterized by disrupted sleep patterns. We used "The War of the Ghosts" test to measure declarative memory and the Alternating Serial Reaction Time (ASRT) task. This enabled us to measure two aspects of nondeclarative memory--general skill learning and sequence-specific learning--separately. Ten children with SDB and 10 healthy controls participated in this study. Our data showed dissociation between declarative and nondeclarative memory in children with SDB. They showed impaired declarative memory, while the sequence-specific and general skill learning was similar to that of healthy controls, in spite of sleep disruption. Our findings suggest that sleep-disordered breathing affects declarative and nondeclarative memory differently in children. Moreover, these findings imply that the disrupted sleep pattern influences the more attention-demanding and cortical structure-guided explicit processes, while the less attention-demanding implicit processes mediated by subcortical structures are preserved.

Behavioral Sleep Problems and their Potential Impact on Developing Executive Function in Children

Bedtime resistance and night waking are common sleep problems throughout childhood, especially in the early years. These sleep problems may lead to difficulties in neurobehavioral functioning, but most research into childhood sleep problems has not emphasized the importance of the developmental context in which disruptions in neurobehavioral and daytime functioning occur. We review the development of sleep as well as executive functioning (EF) in childhood and suggest that EF may be particularly vulnerable to the effects of these common childhood sleep problems because of its prolonged course of maturation. Behavioral problems associated with common sleep problems suggest poor self-regulation in the context of sleep loss, and developing EF skills play important roles in self-regulation. A research agenda that considers a developmental approach to sleep and sleep problems in the context of childhood EF performance is outlined to promote future research in this area.

CITATION

Turnbull K; Reid GJ; Morton JB. Behavioral sleep problems and their potential impact on developing executive function in children. SLEEP 2013;36(7):1077-1084.

Twenty-four hours of total sleep deprivation selectively impairs attentional networks

Performance decrements after sleep loss have been extensively studied and are usually attributed to generic attentional deficits. This claim, however, is based on the view of attention as a unitary construct, despite evidence that it should be considered a multidimensional cognitive ability. The aim of the present study was to evaluate the impact of one night of sleep deprivation on the efficiency of three attentional networks, defined by Posner and Raichle (1994) in anatomical and functional terms, as alerting, orienting, and executive control. Thirty participants performed the Attention Network Test at 9:00 a.m. following two different sleep conditions: baseline (a normal night of sleep) and deprivation (24 hrs of wakefulness). Results showed an overall slowing in reaction times and a significant decrease in accuracy after sleep deprivation. Sleep deprivation selectively affected the three attentional networks, given that only executive control efficacy significantly decreased after sleep deprivation. By contrast, phasic alerting and orienting showed no differences in the two sleep conditions. Thus, performance deficits following sleep deprivation do not reflect global attentional deficits.

Children's sleep and adjustment: a residualized change analysis

We investigated longitudinal relations between children's sleep and symptoms of depression, anxiety, and anger/aggression. We expected that initial sleep problems and increases in these problems over time would be associated with worse adjustment outcomes. The study had 3 waves with 1-year lags. At Time 1 [T1], 128 girls and 123 boys (M age = 8.23 years, SD = 0.73) participated; M ages at Time 2 (T2) and Time 3 (T3) = 9.31 years (SD = 0.79) and 10.28 (SD = 0.99). The sample was diverse in relation to economic adversity and ethnicity (66% European and 34% African American). Higher initial levels and increases in sleep/wake problems or sleepiness over 3 years predicted higher levels of depression and anxiety symptoms at T3, controlling for T1 levels. These associations were more pronounced for girls, African American children, and children from lower socioeconomic status homes. Findings build on a small body of literature addressing links between sleep and adjustment longitudinally and highlight the importance of adequate sleep for children's optimal development, especially within the broader sociocultural milieu..

Evaluating the links between schizophrenia and sleep and circadian rhythm disruption

Sleep and circadian rhythm disruption (SCRD) and schizophrenia are often co-morbid. Here, we propose that the co-morbidity of these disorders stems from the involvement of common brain mechanisms. We summarise recent clinical evidence that supports this hypothesis, including the observation that the treatment of SCRD leads to improvements in both the sleep quality and psychiatric symptoms of schizophrenia patients. Moreover, many SCRD-associated pathologies, such as impaired cognitive performance, are routinely observed in schizophrenia. We suggest that these associations can be explored at a mechanistic level by using animal models. Specifically, we predict that SCRD should be observed in schizophrenia-relevant mouse models. There is a rapidly accumulating body of evidence which supports this prediction, as summarised in this review. In light of these emerging data, we highlight other models which warrant investigation, and address the potential challenges associated with modelling schizophrenia and SCRD in rodents. Our view is that an understanding of the mechanistic overlap between SCRD and schizophrenia will ultimately lead to novel treatment approaches, which will not only ameliorate SCRD in schizophrenia patients, but also will improve their broader health problems and overall quality of life.

Quantitative proteomic analyses of cerebrospinal fluid using iTRAQ in a primate model of iron deficiency anemia

Iron deficiency affects nearly 2 billion people worldwide, with pregnant women and young children being most severely impacted. Sustained anemia during the first year of life can cause cognitive, attention and motor deficits, which may persist despite iron supplementation. We conducted iTRAQ analyses on cerebrospinal fluid (CSF) from infant monkeys (Macaca mulatta) to identify differential protein expression associated with early iron deficiency. CSF was collected from 5 iron-sufficient and 8 iron-deficient anemic monkeys at weaning age (6-7 months) and again at 12-14 months. Despite consumption of iron-fortified food after weaning, which restored hematological indices into the normal range, expression of 5 proteins in the CSF remained altered. Most of the proteins identified are involved in neurite outgrowth, migration or synapse formation. The results reveal novel ways in which iron deficiency undermines brain growth and results in aberrant neuronal migration and connections. Taken together with gene expression data from rodent models of iron deficiency, we conclude that significant alterations in neuroconnectivity occur in the iron-deficient brain, which may persist even after resolution of the hematological anemia. The compromised brain infrastructure could account for observations of behavioral deficits in children during and after the period of anemia.

Age-related decline in controlled retrieval: the role of the PFC and sleep

Age-related cognitive impairments often include difficulty retrieving memories, particularly those that rely on executive control. In this paper we discuss the influence of the prefrontal cortex on memory retrieval, and the specific memory processes associated with the prefrontal cortex that decline in late adulthood. We conclude that preretrieval processes associated with preparation to make a memory judgment are impaired, leading to greater reliance on postretrieval processes. This is consistent with the view that impairments in executive control significantly contribute to deficits in controlled retrieval. Finally, we discuss age-related changes in sleep as a potential mechanism that contributes to deficiencies in executive control that are important for efficient retrieval. The sleep literature points to the importance of slow-wave sleep in restoration of prefrontal cortex function. Given that slow-wave sleep significantly declines with age, we hypothesize that age-related changes in slow-wave sleep could mediate age-related decline in executive control, manifesting a robust deficit in controlled memory retrieval processes. Interventions, like physical activity, that improve sleep could be effective methods to enhance controlled memory processes in late life.

Overlapping prefrontal systems involved in cognitive and emotional processing in euthymic bipolar disorder and following sleep deprivation: a review of functional neuroimaging studies

Prefrontal cortex (PFC) mediated cognitive and emotional processing deficits in bipolar disorder lead to functional limitations even during periods of mood stability. Alterations of sleep and circadian functioning are well-documented in bipolar disorder, but there is little research directly examining the mechanistic role of sleep and/or circadian rhythms in the observed cognitive and emotional processing deficits. We systematically review the cognitive and emotional processing deficits reliant upon PFC functioning of euthymic patients with bipolar disorder and in healthy individuals deprived of sleep. The evidence from two parallel lines of investigation suggests that sleep and circadian rhythms may be involved in the cognitive and emotional processing deficits seen in bipolar disorder through overlapping neurobiological systems. We discuss current models of bipolar highlighting the PFC-limbic connections and discuss inclusion of sleep-related mechanisms. Sleep and circadian dysfunction is a core feature of bipolar disorder and models of neurobiological abnormalities should incorporate chronobiological measures. Further research into the role of sleep and circadian rhythms in cognition and emotional processing in bipolar disorder is warranted.

Modafinil improves event related potentials P300 and contingent negative variation after 24 h sleep deprivation

AIMS

The efficacy of modafinil as a countermeasure in the reduction of cognitive decline following 24 h of sleep deprivation (SD) on subjective sleepiness scales, event-related potential (ERP) P300, and contingent negative variation (CNV) was evaluated.

MAIN METHODS

Eleven healthy males, age 25-30 years participated. The experiment was performed in five sessions on different days between 7 and 8a.m. Session 1, baseline recordings; Session 2, after one night's SD; Session 3, 48 h of recovery from SD; Session 4, after 1 week of Session 1, following one night's SD along with modafinil (400mg/day); Session 5, 48 h of recovery after SD+modafinil.

KEY FINDINGS

Subjective sleepiness scores increased significantly after SD as compared to baseline (P<0.01), but remained unaltered after modafinil supplementation. There was an increase in N100 and P300 peak latencies of ERP following SD (P<0.01), which was reduced with modafinil (P<0.05). There was an increase in CNV M100 and P300 peak latencies after SD (P<0.01) which decreased with the use of modafinil (P<0.05). The CNV reaction time increased following SD (P<0.01) and decreased with the use of modafinil (P<0.05). No significant effects on ERP N200, P200 latencies and P200, P300 amplitudes and CNV N100, M200 peak latencies and M100, M200 amplitudes were observed.

SIGNIFICANCE

The results strongly suggest that modafinil in a dose of 400mg/day, reduces the subjective sleepiness and cognitive decline following 24 h of SD.

Influence of age, circadian and homeostatic processes on inhibitory motor control: a Go/Nogo task study

Introduction

The contribution of circadian system and sleep pressure influences on executive performance as a function of age has never been studied. The aim of our study was to determine the age-related evolution of inhibitory motor control (i.e., ability to suppress a prepotent motor response) and sustained attention under controlled high or low sleep pressure conditions.

Methods

14 healthy young males (mean age  = 23±2.7; 20–29 years) and 11 healthy older males (mean age  = 68±1.4; 66–70 years) were recruited. The volunteers were placed for 40 hours in “constant routine”. In the “Sleep Deprivation SD” condition, the volunteer was kept awake for 40 hours to obtain a high sleep pressure condition interacting with the circadian process. In the “NAP” condition, the volunteer adopted a short wake/sleep cycle (150/75 min) resulting in a low sleep pressure condition to counteract the homeostatic pressure and investigate the circadian process. Performances were evaluated by a simple reaction time task and a Go/Nogo task repeated every 3H45.

Results

In the SD condition, inhibitory motor control (i.e., ability to inhibit an inappropriate response) was impaired by extended wakefulness equally in both age groups (P<.01). Sustained attention (i.e. ability to respond accurately to appropriate stimuli) on the executive task decreased under sleep deprivation in both groups, and even more in young participants (P<.05). In the NAP condition, age did not influence the time course of inhibitory motor control or sustained attention. In the SD and NAP conditions, older participants had a less fluctuating reaction time performance across time of day than young participants (P<.001).

Conclusion

Aging could be a protective factor against the effects of extended wakefulness especially on sustained attention failures due to an attenuation of sleep pressure with duration of time awake.

The effects of a nighttime nap on the error-monitoring functions during extended wakefulness

STUDY OBJECTIVES

To examine the effects of a 1-hr nighttime nap, and the associated sleep inertia, on the error-monitoring functions during extended wakefulness using the 2 event-related potential components thought to reflect error detection and emotional or motivational evaluation of the error, i.e., the error-related negativity/error-negativity (ERN/Ne) and error-positivity (Pe), respectively.

DESIGN

Participants awakened at 07:00 the morning of the experimental day, and performed a stimulus-response compatibility (arrow-orientation) task at 21:00, 02:00, and 03:00.

SETTING

A cognitive task with EEG data recording was performed in a laboratory setting.

PARTICIPANTS

Twenty young adults (mean age 21.3 ± 1.0 yr, 14 males) participated.

INTERVENTIONS

Half of the participants took a 1-hr nap, and the others had a 1-hr awake-rest period from 01:00-02:00.

MEASUREMENTS AND RESULTS

Behavioral performance and amplitude of the Pe declined after midnight (i.e., 02:00 and 03:00) compared with the 21:00 task period in both groups. During the task period starting at 03:00, the participants in the awake-rest condition reported less alertness and showed fewer correct responses than those who napped. However, there were no effects of a nap on the amplitude of the ERN/Ne or Pe.

CONCLUSIONS

Our results suggest that a 1-hr nap can alleviate the decline in subjective alertness and response accuracy during nighttime; however, error-monitoring functions, especially emotional or motivational evaluation of the error, might remain impaired by extended wakefulness even after the nap. This phenomenon could imply that night-shift workers experiencing extended wakefulness should not overestimate the positive effects of a nighttime 1-hr nap during extended wakefulness.

Sleep apnea syndrome and cognition

Obstructive sleep apnea (OSA) is a sleep-related breathing disorder characterized by repetitive episodes of airflow cessation resulting in brief arousals and intermittent hypoxemia. Several studies have documented significant daytime cognitive and behavioral dysfunction that seems to extend beyond that associated with simple sleepiness and that persists in some patients after therapeutic intervention. A still unanswered question is whether cognitive symptoms in OSA are primarily a consequence of sleep fragmentation and hypoxemia, or whether they coexist independently from OSA. Moreover, very little is known about OSA effects on cognitive performances in the elderly in whom an increased prevalence of OSA is present. In this review we will consider recent reports in the association between sleep apnea and cognition, with specific interest in elderly subjects, in whom sleep disturbances and age-related cognitive decline naturally occur. This will allow us to elucidate the behavioral and cognitive functions in OSA patients and to gain insight into age differences in the cognitive impairment. Clinically, these outcomes will aid clinicians in the evaluation of diurnal consequences of OSA and the need to propose early treatment.

Free recall of word lists under total sleep deprivation and after recovery sleep

STUDY OBJECTIVES

One task that has been used to assess memory effects of prior total sleep deprivation (TSD) is the immediate free recall of word lists; however, results have been mixed. A possible explanation for this is task impurity, since recall of words from different serial positions reflects use of distinct types of memory (last words: short-term memory; first and intermediate words: episodic memory). Here we studied the effects of 2 nights of TSD on immediate free recall of semantically unrelated word lists considering the serial position curve.

DESIGN

Random allocation to a 2-night TSD protocol followed by one night of recovery sleep or to a control group.

SETTING

Study conducted under continuous behavioral monitoring.

PARTICIPANTS

24 young, healthy male volunteers.

INTERVENTION

2 nights of total sleep deprivation (TSD) and one night of recovery sleep.

MEASUREMENTS AND RESULTS

Participants were shown five 15 unrelated word-lists at baseline, after one and 2 nights of TSD, and after one night of recovery sleep. We also investigated the development of recall strategies (learning) and susceptibility to interference from previous lists. No free recall impairment occurred during TSD, irrespective of serial position. Interference was unchanged. Both groups developed recall strategies, but task learning occurred earlier in controls and was evident in the TSD group only after sleep recovery.

CONCLUSION

Prior TSD spared episodic memory, short-term phonological memory, and interference, allowed the development of recall strategies, but may have decreased the advantage of using these strategies, which returned to normal after recovery sleep.

EEG correlates of fatigue during administration of a neuropsychological test battery

OBJECTIVE

Mental fatigue, a poorly understood symptom of sports-related concussion, ideally requires assessment across multiple modalities. Our study aimed to examine mental fatigue effects among 10 neurologically normal, athletically active students undergoing typical concussion testing. It is our intention to ultimately address the question whether fatigue effects due to mild traumatic brain injury (mTBI) may become confounded with fatigue effects due to testing effort.

METHODS

Fourteen athletically active and neurologically normal volunteers were initially recruited from Penn State University. Self-reported fatigue, neuropsychological performance, and electroencephalographic (EEG) activity were measured throughout the whole testing duration. EEG measures in frequency domain (e.g., relative power of theta, alpha, and beta bands) were examined over the course of neuropsychological (NP) test administration.

RESULTS

Predicted fatigue effects over the course of testing included: (a) increased self-reported fatigue; (b) increased errors on the Stroop Interference Test; (c) significantly increased relative power of theta activity during the Stroop Interference Test in frontal-central and parietal regions; and (d) migration of alpha activation from the occipital to anterior (left parietal and pre-central) regions during the Stroop Interference task administered at the beginning compared with the end of testing.

CONCLUSIONS

Results supported predictions related to subjective fatigue and cognitive performance and offered partial support for predictions related to EEG activation patterns over the course of administering the NP testing.

SIGNIFICANCE

Neurologically intact and athletically active college students demonstrate effects related to fatigue after undergoing a typical sports concussion assessment battery, including an increase in subjectively experienced fatigue, a decrease in cognitive task performance accuracy and associated modulations in EEG activity. This finding should be considered by clinical practitioners while evaluating the symptoms of concussion and making a decision regarding the return-to-sport participation.

Spatial reversal learning is robust to total sleep deprivation

Sleep deprivation affects cognitive functions that depend on the prefrontal cortex (PFC) such as cognitive flexibility, and the consolidation of newly learned information. The identification of cognitive processes that are either robustly sensitive or robustly insensitive to the same experimental sleep deprivation procedure, will allow us to better focus on the specific effects of sleep on cognition, and increase understanding of the mechanisms involved. In the present study we investigate whether sleep deprivation differentially affects the two separate cognitive processes of acquisition and consolidation of a spatial reversal task. After training on a spatial discrimination between two levers in a Skinner box, male Wistar rats were exposed to a reversal of the previously learned stimulus-response contingency. We first evaluated the effect of sleep deprivation on the acquisition of reversal learning. Performance on reversal learning after 12h of sleep deprivation (n=12) was compared to performance after control conditions (n=12). The second experiment evaluated the effect of sleep deprivation on the consolidation of reversal learning; the first session of reversal learning was followed by 3h of nap prevention (n=8) or undisturbed control conditions (n=8). The experiments had sufficient statistical power (0.90 and 0.81, respectively) to detect differences with medium effect sizes. Neither the acquisition, nor the consolidation, of reversal learning was affected by acute sleep deprivation. Together with previous findings, these results help to further delineate the role of sleep in cognitive processing.

Switch-task performance in rats is disturbed by 12 h of sleep deprivation but not by 12 h of sleep fragmentation

STUDY OBJECTIVES

Task-switching is an executive function involving the prefrontal cortex. Switching temporarily attenuates the speed and/or accuracy of performance, phenomena referred to as switch costs. In accordance with the idea that prefrontal function is particularly sensitive to sleep loss, switch-costs increase during prolonged waking in humans. It has been difficult to investigate the underlying neurobiological mechanisms because of the lack of a suitable animal model. Here, we introduce the first switch-task for rats and report the effects of sleep deprivation and inactivation of the medial prefrontal cortex.

DESIGN

Rats were trained to repeatedly switch between 2 stimulus-response associations, indicated by the presentation of a visual or an auditory stimulus. These stimulus-response associations were offered in blocks, and performance was compared for the first and fifth trials of each block. Performance was tested after exposure to 12 h of total sleep deprivation, sleep fragmentation, and their respective movement control conditions. Finally, it was tested after pharmacological inactivation of the medial prefrontal cortex.

SETTINGS

Controlled laboratory settings.

PARTICIPANTS

15 male Wistar rats.

MEASUREMENTS & RESULTS

Both accuracy and latency showed switch-costs at baseline. Twelve hours of total sleep deprivation, but not sleep fragmentation, impaired accuracy selectively on the switch-trials. Inactivation of the medial prefrontal cortex by local neuronal inactivation resulted in an overall decrease in accuracy.

CONCLUSIONS

We developed and validated a switch-task that is sensitive to sleep deprivation. This introduces the possibility for in-depth investigations on the neurobiological mechanisms underlying executive impairments after sleep disturbance in a rat model.

A prospective study of the relationship between musculoskeletal or psychological complaints and muscular responses to standardized cognitive and motor tasks in a working population

The present study sought to determine the relationship between musculoskeletal or psychological complaints and muscular responses to standardized cognitive and motor tasks. The prospective study design examined (i) whether complaint severity predicts muscular responses during standardized tasks and (ii) whether the muscular responses predict changes in complaint severity over one year. Musculoskeletal and psychological complaints were recorded by monthly reports the four months preceding and 12 months succeeding a work session in the laboratory; complaint-severity indices were computed from complaint-severity scores (intensity scorexduration score). Surface electromyography (EMG) was recorded bilaterally from the upper trapezius, middle deltoid, and forearm extensor muscles in 45 post-office workers (30 women) during two identical task series. Between the series, exhausting submaximal muscle contractions (25% of peak torque) were performed. In adjusted regression models, no relations between musculoskeletal complaints the last four months and muscle activity during the task series were found. However, psychological complaints the last four months predicted higher muscle activity levels and a steeper rise in muscle activity in the muscles not engaged in motor task performance. Sleep disturbance was the strongest individual predictor of increased muscle responses. In contrast, psychological complaints the last four months predicted lower EMG levels in the task-engaged muscle during the complex-choice-reaction-time tasks. None of the muscle-activity responses to the standardized tasks predicted changes in severity of musculoskeletal or psychological complaints over the subsequent one-year period. In conclusion, psychological complaints predict different responses in task-engaged and non-involved muscles during cognitive and motor tasks. Musculoskeletal complaints did not predict responses to the tasks.

Managing neurobehavioral capability when social expediency trumps biological imperatives

Sleep, which is evolutionarily conserved across species, is a biological imperative that cannot be ignored or replaced. However, the percentage of habitually sleep-restricted adults has increased in recent decades. Extended work hours and commutes, shift work schedules, and television viewing are particularly potent social factors that influence sleep duration. Chronic partial sleep restriction, a product of these social expediencies, leads to the accumulation of sleep debt over time and consequently increases sleep propensity, decreases alertness, and impairs critical aspects of cognitive functioning. Significant interindividual variability in the neurobehavioral responses to sleep restriction exists-this variability is stable and phenotypic-suggesting a genetic basis. Identifying vulnerability to sleep loss is essential as many adults cannot accurately judge their level of impairment in response to sleep restriction. Indeed, the consequences of impaired performance and the lack of insight due to sleep loss can be catastrophic. In order to cope with the effects of social expediencies on biological imperatives, identification of biological (including genetic) and behavioral markers of sleep loss vulnerability as well as development of technological approaches for fatigue management are critical.

Habitual Sleep, Reasoning, and Processing Speed in Older Adults with Sleep Complaints

The relationship between habitual sleep and cognition in older adults with sleep complaints is poorly understood, because research has focused on younger adults, used experimental or retrospective quasi-experimental designs, and generally produced equivocal results. Prospective studies using sleep diaries are rare, but may provide important insights into this relationship as they offer greater ecological validity and allow for examination of the impact of night-to-night variability in sleep (an often overlooked aspect of sleep) on cognitive performance. Seventy-two older adults (M(age) = 70.18 years, SD(age) = 7.09 years) completed fourteen consecutive days of sleep diaries and paper/pencil self-administered cognitive tasks, including measures of processing speed (Symbol Digit) and reasoning (Letter Series). Regression analyses revealed increased average total wake time (TWT) during the night was associated with higher Symbol Digit scores, β = 0.45, P < 0.05. Night-to-night variability in either total sleep time (TST) or TWT was not associated with either cognitive measure. Implications and potential explanations for these initially counterintuitive findings are discussed.

Further evidence for executive dysfunction in subjects with RLS from a non-clinical sample

OBJECTIVE AND BACKGROUND

Previous studies exploring cognitive functioning in RLS have either relied on medication free subjects sampled within a clinical context or on subjects with RLS symptoms identified within population samples. However, in contrast to clinical samples, population studies so far have not excluded the use of antidepressants, hypnotics, or RLS relevant medication, and study subjects were exclusively older in age. We therefore report on cognitive functioning in predominantly middle-aged individuals with RLS symptoms sampled from the general population and free of mental disorders and of hypnotic, psychopharmacological, or RLS relevant medication.

METHODS

Participants with RLS symptoms and individually matched controls were identified within the MARS control study, a non-clinical control group study of 550 participants between 18 and 75 years. Cognitive functioning was assessed with the Trail Making Test A and B and a computerized German version of the Wisconsin Card Sorting Test (WCST). Performance was compared between 41 participants with RLS and 133 controls, and between a subgroup of 10 participants with frequent RLS symptoms (≥ 2/week) and 36 matched controls.

RESULTS

There was no difference in cognitive functioning for the complete group of participants with RLS and controls. However, participants with frequent RLS symptoms showed impaired performance in the WCST.

CONCLUSION

The results of this study add to the evidence that executive functioning is impaired in individuals with frequent RLS.

The impact of one night of sleep deprivation on moral judgments

Recent studies have shown the existence of a relationship between sleep and moral judgment. In this study, we investigated whether one night of sleep deprivation affects the ability to judge the appropriateness of moral dilemmas. Forty-eight students had to judge 30 moral dilemmas at test, after a night of home sleep, and another 30 dilemmas at retest, following one night of continuous wakefulness. The 60 dilemmas (20 moral impersonal, 20 moral personal, and 20 non-moral) were selected from Greene's dilemmas. Both groups judged the appropriateness of personal and impersonal dilemmas in the same way. A close to significant effect of sleep deprivation was observed on the reaction times for impersonal moral dilemmas, to which the deprived subjects responded faster (p = .05) than the control subjects. However, this was not the case for personal ones, for which no difference was significant. This result shows a greater ease/speed in responding to the (impersonal) dilemmas, which induce low emotional engagement after sleep deprivation, although the willingness to accept moral violations is not affected. This suggests that one night of sleep loss selectively influences the response speed only for moral impersonal dilemmas, probably due to disinhibition processes. The quality of moral judgment dilemmas does not seem to be easily influenced by a single night of sleep deprivation, but only by a longer lack of sleep.

The cognitive cost of sleep lost

A substantial body of literature supports the intuitive notion that a good night's sleep can facilitate human cognitive performance the next day. Deficits in attention, learning & memory, emotional reactivity, and higher-order cognitive processes, such as executive function and decision making, have all been documented following sleep disruption in humans. Thus, whilst numerous clinical and experimental studies link human sleep disturbance to cognitive deficits, attempts to develop valid and reliable rodent models of these phenomena are fewer, and relatively more recent. This review focuses primarily on the cognitive impairments produced by sleep disruption in rodent models of several human patterns of sleep loss/sleep disturbance. Though not an exclusive list, this review will focus on four specific types of sleep disturbance: total sleep deprivation, experimental sleep fragmentation, selective REM sleep deprivation, and chronic sleep restriction. The use of rodent models can provide greater opportunities to understand the neurobiological changes underlying sleep loss induced cognitive impairments. Thus, this review concludes with a description of recent neurobiological findings concerning the neuroplastic changes and putative brain mechanisms that may underlie the cognitive deficits produced by sleep disturbances.

A survey of sleep deprivation patterns and their effects on cognitive functions of residents and interns in Korea

OBJECTIVE

To investigate the effects of sleep deprivation on physical health, cognition, and work performance in residents and interns who suffer from chronic sleep deprivation.

METHODS

Fifty-eight residents and interns were recruited in this study. They completed sleep diary for 2 weeks and questionnaires including health complaints, daytime sleepiness and work performance, and were evaluated with actigraphy. Stroop test, continuous performance test (CPT), trail-making test (TMT) and Korean-California verbal learning test (K-CVLT) were done as neuropsychological evaluations. Subjects were divided into severe sleep deprived (S-SD, average night sleep less than 4 h), mild to moderate deprived (M-SD, 4-6 h), and non-sleep deprived (Non-SD, more than 6 h) groups.

RESULTS

Forty-one subjects (70.7%) were sleep-deprived. Mean sleep duration was 5.0±1.2 h/night and work duration was 14.9±2.7 h/day. The S-SD group showed higher Epworth Sleepiness Scales than M-SD and Non-SD groups. Severe sleep deprivation was associated with higher level of stress, more frequent attention deficit, and difficulty in learning (P<0.05), but not with decreased neuropsychological test results.

CONCLUSION

These results suggested that sleep deprivation in residents and interns might affect their health as well as work performance that might influence the quality of patient care, although active compensatory brain mechanisms could be involved to preserve their performance.

An hour less sleep is a risk factor for childhood conduct problems

BACKGROUND

There is emerging evidence that sleep problems in childhood may have enduring consequences. Studies using parental and objective sleep measurement suggest that sleep difficulties in children may be associated with behavioural problems. However, the findings using objective sleep measures are inconsistent and it is not clear what aspects of sleep quality are associated with daytime behavioural difficulties. The aim of this paper is to identify which behavioural symptoms are best predicted by actigraphic sleep measures in a general population sample of school-aged children aged 6-11 years.

METHODS

Actigraphy was used to measure sleep in 91 typically developing children aged 6-11 years for 6 days. Parents completed the Strengths and Difficulties Questionnaire (SDQ). A series of multivariate linear regression models were computed to analyse the effects of sleep on SDQ subscales.

RESULTS

Sleep did not predict emotional symptoms or hyperactivity. After controlling for age and gender, sleep accounted for 18% of the variance in conduct problems. Only actual sleep time in minutes made a significant contribution to the model.

CONCLUSIONS

A child who sleeps 1 h less than the average child may be at risk of conduct problems. Clinicians should consider routinely screening for sleep difficulties when assessing children with conduct problems.

EEG spectral analysis of apnoeic events confirms visual scoring in childhood sleep disordered breathing

PURPOSE

This study compared electroencephalogram (EEG) spectral analysis with standard visual scoring to assess the validity of clinical classification of arousals at respiratory event termination in children with obstructive sleep apnoea (OSA).

METHODS

Twenty children (six M/14 F) aged 7-12 years, diagnosed with moderate to severe OSA participated in this study. Overnight polysomnography was performed, and sleep stages and arousals visually scored using clinical paediatric measures. The EEG was spectrally analysed in six 5-s epochs across respiratory events, namely two consecutive 5-s epochs pre-event onset and a 5s epoch post-event onset, 5-s before event termination, and two contiguous 5-s epochs post-event termination. EEG spectral power distribution was compared across respiratory events visually categorised as full cortical arousals, subcortical activations, or non-arousals using specialised software (Sleep Research System 5.0).

RESULTS

There was no difference in power spectra between events in REM and NREM sleep and these were combined. There was a statistically significant fall from pre-arousal baseline values in delta and theta spectral power at respiratory event terminations associated with cortical arousals only. No change in power was detected at respiratory event terminations associated with subcortical activations or non-arousals.

CONCLUSIONS

The lack of significant EEG spectral power changes at respiratory event terminations not associated with visually identified cortical arousals indicates undetected micro-arousals are not present. The results support the validity of clinical classifications of arousals at respiratory event termination.

A meta-analysis of the impact of short-term sleep deprivation on cognitive variables

A substantial amount of research has been conducted in an effort to understand the impact of short-term (<48 hr) total sleep deprivation (SD) on outcomes in various cognitive domains. Despite this wealth of information, there has been disagreement on how these data should be interpreted, arising in part because the relative magnitude of effect sizes in these domains is not known. To address this question, we conducted a meta-analysis to discover the effects of short-term SD on both speed and accuracy measures in 6 cognitive categories: simple attention, complex attention, working memory, processing speed, short-term memory, and reasoning. Seventy articles containing 147 cognitive tests were found that met inclusion criteria for this study. Effect sizes ranged from small and nonsignificant (reasoning accuracy: g = -0.125, 95% CI [-0.27, 0.02]) to large (lapses in simple attention: g = -0.776, 95% CI [-0.96, -0.60], p < .001). Across cognitive domains, significant differences were observed for both speed and accuracy; however, there were no differences between speed and accuracy measures within each cognitive domain. Of several moderators tested, only time awake was a significant predictor of between-studies variability, and only for accuracy measures, suggesting that heterogeneity in test characteristics may account for a significant amount of the remaining between-studies variance. The theoretical implications of these findings for the study of SD and cognition are discussed.

Relations between physiological and cognitive regulatory systems: infant sleep regulation and subsequent executive functioning

The aim of this report was to investigate the prospective links between infant sleep regulation and subsequent executive functioning (EF). The authors assessed sleep regulation through a parent sleep diary when children were 12 and 18 months old (N = 60). Child EF was assessed at 18 and 26 months of age. Higher proportions of total sleep occurring at night time, at both 12 and 18 months, were related to better performance on executive tasks, especially those involving a strong impulse control component. Most relations held above family socioeconomic status, prior mental development and concurrent verbal ability. These findings add to previous results with school-age children in suggesting that sleep favors the development of higher order cognitive functions requiring prefrontal cortex involvement.

Alerting, orienting and executive control: the effects of sleep deprivation on attentional networks

Sleep deprivation alters attentional functions like vigilance or tonic alerting (i.e., sustaining an alert state over a period of time). However, the effects of sleep loss on both orienting and executive control are still not clear, and no study has assessed whether sleep deprivation might affect the relationships among these three attentional systems. In order to investigate the efficiency of the three attentional networks--alerting, orienting and executive control--within a single task, we used the Attention Network Test (ANT). Eighteen right-handed male participants took part in the experiment, which took place on two consecutive days. On the first day, each participant performed a 20 min training session of the ANT. On the second day, participants remained awake for 24 h during which time the ANT was performed once at 5:00 p.m. and once at 4:00 a.m. Results showed an overall slowing of reaction times in the nocturnal session, indicating a strong decrease in vigilance. Furthermore, sleep deprivation did affect attentional orienting and executive control. Results are consistent with the hypothesis that the tonic component of alerting interacts with both attentional orienting and executive functions.

Sleep, intelligence and cognition in a developmental context: differentiation between traits and state-dependent aspects

This article addresses associations between sleep, cognition and intelligence in a developmental context and clarifies the terminology. Research must differentiate between aspects related to general underlying traits and those aspects that are characterized by state-dependent fluctuations.

Cognitive-behavioral therapy for insomnia improves attentional function in fibromyalgia syndrome: A pilot, randomized controlled trial

This pilot, randomized controlled trial analyzed the effects of a cognitive behavioral therapy (CBT, n = 20) for insomnia vs a sleep hygiene (SH, n = 20) program on the three attentional networks (alertness, orienting, and executive function) and other additional outcome measures (sleep, pain, depression, anxiety, and daily functioning) of fibromyalgia patients. The CBT group showed significant improvement in alertness ( F(1, 28) = 11.84, p = .0018), executive functioning ( F(1, 28) = 15.76, p = .00059), sleep quality ( F(1, 38) = 6.33, p = .016), and a trend to improvement in daily functioning ( p > .06), as compared with the SH group. The improvement in executive functioning was significantly related to the changes in sleep (r = 0.40, p = .026). A CBT for insomnia represents a useful intervention in fibromyalgia patients not only regarding sleep disturbance but also attentional dysfunction and probably daily functioning.

Physical activity and cognition in older adults: the potential of Tai Chi Chuan

The purpose of this article is to review the potential of Tai Chi Chuan as a mode of physical activity that could have cognitive benefits for older adults and to provide potential directions for future research. A brief introduction to Tai Chi Chuan and its related physical benefits is provided. In addition, the empirical literature related to Tai Chi Chuan and cognition is reviewed. Potential mediators of the relationship between Tai Chi Chuan and cognition, including physical resources, disease status, and mental resources, are discussed. Based on the limitations of the extant literature, it is argued that future research in this area must provide more detailed descriptions of Tai Chi Chuan, particularly in terms of intensity and program progression. Consideration of the specific type of cognition that is expected to benefit is also encouraged, and approaches for further efforts to understand how Tai Chi Chuan affects cognition are recommended.