Clare Anderson

Sleep deprivation lowers inhibition and enhances impulsivity to negative stimuli

Sleep deprivation has previously been shown to intensify neural and autonomic responses to increasingly negative stimuli. Here, we report how this potential bias to negative stimuli manifests itself in behavioural performance. One night of sleep loss led to increased impulsivity to negative stimuli, such that sleep deprived individuals had an increased failure to inhibit a response and faster incorrect responses. This enhanced reactivity to negative stimuli has important consequences outside the confines of the laboratory.

Prefrontal cortex: Links between low frequency delta EEG in sleep and neuropsychological performance in healthy, older people

Low frequency (< 1 Hz) delta EEG in sleep is of increasing interest as it indicates cortical reorganization, especially in the prefrontal cortex (PFC). Other research shows that delta power in sleep is positively linked to waking cerebral metabolic rate. Such findings suggest that < 1 Hz activity may reflect waking performance at neuropsychological tests specific to the PFC. We investigated this unexplored area. Sleep EEGs (Fp1-F3, Fp2-F4, O1-P3, O2-P4) were recorded in 24 healthy 61-75-year-olds. We found significant associations between 0.5-1.0 Hz power from the left frontal EEG channel, in the first non-REM period, and performance at tasks more specific to the left PFC (e.g., nonverbal planning and verbal fluency). This association was absent from the posterior channels. Neither age nor response times were confounding factors. This potential sleep EEG marker for PFC neuropsychological function in healthy, older people also points to further uses of the sleep EEG in understanding the role of sleep.

Bargaining and trust: the effects of 36‐h total sleep deprivation on socially interactive decisions

Although it is well known that sleep loss results in poor judgement and decisions, little is known about the influence of social context in these processes. Sixteen healthy young adults underwent three games involving bargaining (‘Ultimatum’ and ‘Dictator’) and trust, following total sleep deprivation (TSD) and during rested wakefulness (RW), in a repeated‐measures, counterbalanced design. To control for repeatability, a second group (n = 16) was tested twice under RW conditions. Paired anonymously with another individual, participants made their simple social interaction decisions facing real monetary incentives. For bargaining, following TSD participants were more likely to reject unequal‐split offers made by their partner, despite the rejection resulting in a zero monetary payoff for both participants. For the trust game, participants were less likely to place full trust in their anonymous partner. Overall, we provide novel evidence that following TSD, the conflict between personal financial gain and payoff equality is focused upon avoidance of unfavourable inequality (i.e. unfairness). This results in the rejection of unfair offers at personal monetary cost, and the lack of full trust which would expose one to being exploited in the interaction. As such, we suggest that within a social domain decisions may be more influenced by emotion following TSD, which has fundamental consequences for real‐world decision‐making involving social exchange.

Objective and subjective measures of sleepiness, and their associations with on-road driving events in shift workers

To assess the relationships between sleepiness and the incidence of adverse driving events in nurses commuting to and from night and rotating shifts, 27 rotating and permanent night shift‐working nurses were asked to complete daily sleep and duty logs, and wear wrist‐activity monitors for 2 weeks (369 driving sessions). During all commutes, ocular measures of drowsiness, including the Johns Drowsiness Scale score, were assessed using the Optalert™ system. Participants self‐reported their subjective sleepiness at the beginning and end of each drive, and any events that occurred during the drive. Rotating shift nurses reported higher levels of sleepiness compared with permanent night shift nurses. In both shift‐working groups, self‐reported sleepiness, drowsiness and drive events were significantly higher during commutes following night shifts compared with commutes before night shifts. Strong associations were found between objective drowsiness and increased odds of driving events during commutes following night shifts. Maximum total blink duration (mean = 7.96 s) during the drive and pre‐drive Karolinska Sleepiness Scale (mean = 5.0) were associated with greater incidence of sleep‐related events [OR, 5.35 (95% CI, 1.32, 21.60), OR, 1.69 (95% CI, 1.04, 2.73), respectively]. Inattention was strongly associated with a Johns Drowsiness Scale score equal to or above 4.5 [OR, 4.58 (95% CI, 1.26–16.69)]. Hazardous driving events were more likely to occur when drivers had been awake for 16 h or more [OR, 4.50 (95% CI, 1.81, 11.16)]. Under real‐world driving conditions, shift‐working nurses experience high levels of drowsiness as indicated by ocular measures, which are associated with impaired driving performance following night shift work.

Nonlinear analysis of EEG during NREM sleep reveals changes in functional connectivity due to natural aging

The spatial organization of nonlinear interactions between different brain regions during the first NREM sleep stage is investigated. This is achieved via consideration of four bipolar electrode derivations, Fp1F3, Fp2F4, O1P3, O2P4, which are used to compare anterior and posterior interhemispheric interactions and left and right intrahemispheric interactions. Nonlinear interdependence is detected via application of a previously written algorithm, along with appropriately generated surrogate data sets. It is now well understood that the output of neural systems does not scale linearly with inputs received and, thus, the study of nonlinear interactions in EEG is crucial. This approach also offers significant advantages over standard linear techniques, in that the strength, direction, and topography of the interdependencies can all be calculated and considered. Previous research has linked delta activity during the first NREM sleep stage to performance on frontally activating tasks during waking hours. We demonstrate that nonlinear mechanisms are the driving force behind this delta activity. Furthermore, evidence is presented to suggest that the aging brain calls upon the right parietal region to assist the pre‐frontal cortex. This is highlighted by statistically significant differences in the rates of interdependencies between the left pre‐frontal cortex and the right parietal region when comparing younger subjects (<23 years) with older subjects (>60 years). This assistance has been observed in brain‐imaging studies of sleep‐deprived young adults, suggesting that similar mechanisms may play a role in the event of healthy aging. Additionally, the contribution to the delta rhythm via nonlinear mechanisms is observed to be greater in older subjects. Hum. Brain Mapping 23:73–84, 2004.

High risk of near-crash driving events following night-shift work

Significance Drowsy driving is a major public health issue, particularly impacting the 9.5 million shift workers in America. Previous reports have assessed the impact of night work on driving in driving simulators. This real-vehicle driving study demonstrated increased objective and subjective drowsiness and degraded daytime driving performance in 16 night-shift workers while driving after a night of work, deteriorating with drive duration. No near-crashes occurred during driving after a night of sleep; 11 occurred during driving after night-work; all near-crashes occurred after at least 45 min of driving. Policy makers and night-workers should consider avoiding/minimizing driving or deploying effective countermeasures when driving after night-shift work to reduce drowsy driving and preventable crashes and injuries in this high-risk population. Night-shift workers are at high risk of drowsiness-related motor vehicle crashes as a result of circadian disruption and sleep restriction. However, the impact of actual night-shift work on measures of drowsiness and driving performance while operating a real motor vehicle remains unknown. Sixteen night-shift workers completed two 2-h daytime driving sessions on a closed driving track at the Liberty Mutual Research Institute for Safety: (i) a postsleep baseline driving session after an average of 7.6 ± 2.4 h sleep the previous night with no night-shift work, and (ii) a postnight-shift driving session following night-shift work. Physiological measures of drowsiness were collected, including infrared reflectance oculography, electroencephalography, and electrooculography. Driving performance measures included lane excursions, near-crash events, and drives terminated because of failure to maintain control of the vehicle. Eleven near-crashes occurred in 6 of 16 postnight-shift drives (37.5%), and 7 of 16 postnight-shift drives (43.8%) were terminated early for safety reasons, compared with zero near-crashes or early drive terminations during 16 postsleep drives (Fishers exact: P = 0.0088 and P = 0.0034, respectively). Participants had a significantly higher rate of lane excursions, average Johns Drowsiness Scale, blink duration, and number of slow eye movements during postnight-shift drives compared with postsleep drives (3.09/min vs. 1.49/min; 1.71 vs. 0.97; 125 ms vs. 100 ms; 35.8 vs. 19.1; respectively, P < 0.05 for all). Night-shift work increases driver drowsiness, degrading driving performance and increasing the risk of near-crash drive events. With more than 9.5 million Americans working overnight or rotating shifts and one-third of United States commutes exceeding 30 min, these results have implications for traffic and occupational safety.

Placebo response to caffeine improves reaction time performance in sleepy people

Caffeine is the most widely used stimulant to counteract sleepiness. However, little is known about any placebo effect of caffeine in sleepy people and the effect of suggestibility. Over a 95 min test period, and in a counterbalanced design, 16 young healthy adults underwent 3 × 30 min sessions at the psychomotor vigilance test (PVT), during an early afternoon ‘dip’ enhanced by a prior nights sleep restriction (5 h). On both occasions they were given a cup of a decaffeinated coffee; once when the participant was verbally primed to suggest the coffee was caffeinated (Placebo) and on the other under neutral priming (Control). There were significantly fewer lapses and shorter reaction times following Placebo, for the initial two 30 min sessions, indicating that suggestion about consuming caffeine was effective in improving performance in moderately sleepy people. Copyright

Impact of common diabetes risk variant in MTNR1B on sleep, circadian and melatonin physiology

The risk of type 2 diabetes (T2D) is increased by abnormalities in sleep quantity and quality, circadian alignment, and melatonin regulation. A common genetic variant in a receptor for the circadian-regulated hormone melatonin (MTNR1B) is associated with increased fasting blood glucose and risk of T2D, but whether sleep or circadian disruption mediates this risk is unknown. We aimed to test if MTNR1B diabetes risk variant rs10830963 associates with measures of sleep or circadian physiology in intensive in-laboratory protocols (n = 58–96) or cross-sectional studies with sleep quantity and quality and timing measures from self-report (n = 4,307–10,332), actigraphy (n = 1,513), or polysomnography (n = 3,021). In the in-laboratory studies, we found a significant association with a substantially longer duration of elevated melatonin levels (41 min) and delayed circadian phase of dim-light melatonin offset (1.37 h), partially mediated through delayed offset of melatonin synthesis. Furthermore, increased T2D risk in MTNR1B risk allele carriers was more pronounced in early risers versus late risers as determined by 7 days of actigraphy. Our results provide the surprising insight that the MTNR1B risk allele influences dynamics of melatonin secretion, generating a novel hypothesis that the MTNR1B risk allele may extend the duration of endogenous melatonin production later into the morning and that early waking may magnify the diabetes risk conferred by the risk allele.

Frontal and parietal activity after sleep deprivation is dependent on task difficulty and can be predicted by the fMRI response after normal sleep.

Sleep disturbance in neurological and psychiatric disorders is common and associated with diminished cognitive functioning. Whilst these deficits can be localised predominantly to frontal and parietal regions, there have been reported inconsistencies which may be due to differences in the difficulty and type of task. In the present study we examined the effects of sleep deprivation (SD) whilst parametrically varying working memory load using an n-back task. 20 right-handed males performed the n-back task after a night of normal sleep (RW: rested wakefulness) and after approximately 31 h of SD. Comparison of load responsive cerebral activation identified two clusters where the parametric response was altered after SD. In the right ventrolateral prefrontal cortex activity was reduced at the most difficult working memory load, whereas in the right inferior parietal lobe activity was increased at the simplest working memory load. The strength of activation in both of these regions during RW predicted the response of those same regions to SD. While the ability to predict signal change has previously been demonstrated using behavioural measures, to our knowledge this is the first study to show that the neuronal effects of SD can be predicted based upon activation during a normal rested condition.

Disorganized attachment in infancy predicts greater amygdala volume in adulthood

Early life stress in rodents is associated with increased amygdala volume in adulthood. In humans, the amygdala develops rapidly during the first two years of life. Thus, disturbed care during this period may be particularly important to amygdala development. In the context of a 30-year longitudinal study of impoverished, highly stressed families, we assessed whether disorganization of the attachment relationship in infancy was related to amygdala volume in adulthood. Amygdala volumes were assessed among 18 low-income young adults (8M/10F, 29.33±0.49years) first observed in infancy (8.5±5.6months) and followed longitudinally to age 29. In infancy (18.58±1.02mos), both disorganized infant attachment behavior and disrupted maternal communication were assessed in the standard Strange Situation Procedure (SSP). Increased left amygdala volume in adulthood was associated with both maternal and infant components of disorganized attachment interactions at 18 months of age (overall r=0.679, p<0.004). Later stressors, including childhood maltreatment and attachment disturbance in adolescence, were not significantly related to left amygdala volume. Left amygdala volume was further associated with dissociation and limbic irritability in adulthood. Finally, left amygdala volume mediated the prediction from attachment disturbance in infancy to limbic irritability in adulthood. Results point to the likely importance of quality of early care for amygdala development in human children as well as in rodents. The long-term prediction found here suggests that the first two years of life may be an early sensitive period for amygdala development during which clinical intervention could have particularly important consequences for later child outcomes.