It is not fully understood why we need to sleep, although it is evident that sleep loss has consequences for many emotional and cognitive functions. The last couple of decades, sleep researchers have been increasingly devoted to better understand the relationship between sleep and affect. However, it is still poorly understood how sleep deprivation influences the way in which affective information is processed. The aim of this thesis was to investigate if there is a bias towards affective information after sleep deprivation and whether such bias influence information processing.

Study I tested reinforcement learning from positive as compared to negative feedback after two nights of sleep restriction. There were no indications of the expected reward-seeking behavior in generalized learning or in the learning strategy. A slowing in learning rate inferred from computational modeling was observed primarily for negative feedback. This could be indicative of a slowing in memory integration. It is unclear if the dopamine alterations proposed to cause reward-seeking behavior after total sleep deprivation are also implicated after sleep restriction.

Study II examined the neurophysiological response of the competition of attention between unpleasant and neutral pictures after two nights of sleep restriction. We found no alterations of sleep restriction on attention in relation to picture valence, or on executive control of attention. Despite observations of an increased sleepiness, an impaired sustained attention, and reduced positive affect, the few hours of allowed sleep may have been enough to counteract an affective bias and an executive control impairment.

Study III tested if one night of total sleep deprivation altered working memory for positive, negative, or neutral pictures using two levels of working memory load. Results showed that working memory accuracy was generally impaired after sleep deprivation, independent of picture valence. However, in the sleep deprived group we observed faster responses to positive and slower responses to negative pictures. These results could indicate a bias towards both positive and negative pictures, but with opposite consequences on working memory speed.

Study IV used the same protocol as Study III to combinedly test two common findings among older adults: That they prioritize positive over negative stimuli (the positivity effect), and that they are less affected by sleep deprivation. Working memory performance was overall better for positive than negative pictures, with no differences between the sleep conditions. This positivity effect was only present in the low working memory load condition. These results show that even after a state-dependent challenge such as sleep deprivation, the positivity effect remains in older adults, at least when working memory load is low.

Overall, the Studies in this thesis demonstrate signs of affective bias as well as lack thereof after total and partial sleep deprivation. The use of a diverse set of tasks and methodology may have contributed to the discrepancies in the findings, but it also highlights that we have yet to fully understand how lack of sleep may influence the processing of affectively valuable information.

To learn from feedback (trial and error) is essential for all species. Insufficient sleep has been found to reduce the sensitivity to feedback as well as increase reward sensitivity. To determine whether insufficient sleep alters learning from positive and negative feedback, healthy participants (n = 32, mean age 29.0 years, 18 women) were tested once after normal sleep (8 hr time in bed for 2 nights) and once after 2 nights of sleep restriction (4 hr/night) on a probabilistic selection task where learning behaviour was evaluated in three ways: as generalised learning, short-term win-stay/lose-shift learning strategies, and trial-by-trial learning rate. Sleep restriction did not alter the sensitivity to either positive or negative feedback on generalised learning. Also, short-term win-stay/lose-shift strategies were not affected by sleep restriction. Similarly, results from computational models that assess the trial-by-trial update of stimuli value demonstrated no difference between sleep conditions after the first block. However, a slower learning rate from negative feedback when evaluating all learning blocks was found after sleep restriction. Despite a marked increase in sleepiness and slowed learning rate for negative feedback, sleep restriction did not appear to alter strategies and generalisation of learning from positive or negative feedback.

The emotional dysregulation and impaired working memory found after sleep loss can have severe implications for our daily functioning. Considering the intertwined relationship between emotion and cognition in stimuli processing, there could be further implications of sleep deprivation in high‐complex emotional situations. Although studied separately, this interaction between emotion and cognitive processes has been neglected in sleep research. The aim of the present study was to investigate the effect of 1 night of sleep deprivation on emotional working memory. Sixty‐one healthy participants (mean age: 23.4 years) were either sleep deprived for 1 night (n = 30) or had a normal night’s sleep (n = 31). They performed an N‐back task with two levels of working memory load (1‐back and 3‐back) using positive, neutral and negative picture scenes. Sleep deprivation, compared with full night sleep, impaired emotional working memory accuracy, but not reaction times. The sleep‐deprived participants, but not the controls, responded faster to positive than to negative and neutral pictures. The effect of sleep deprivation was similar for both high and low working memory loads. The results showed that although detrimental in terms of accuracy, sleep deprivation did not impair working memory speed. In fact, our findings indicate that positive stimuli may facilitate working memory processing speed after sleep deprivation.

Sleep deprivation commonly impairs affective regulation and causes worse mood. However, the majority of previous research concerns young adults. Because susceptibility to sleep deprivation and emotion regulation change distinctively across adult age, we tested here the hypothesis that the effect of sleep deprivation on mood is stronger in young than in older adults. In an experimental design, young (18–30 years) and older adults (60–72 years) participated in either a sleep control (young, n = 63; older, n = 47) or a total sleep deprivation condition (young, n = 61; older, n = 47). Sleepiness, mood and common symptoms of sleep deprivation were measured using established questionnaires and ratings. Sleep‐deprived participants felt more sleepy, stressed and cold, and reported lower vigour and positive affect, regardless of age. All the other outcome measures (negative affect, depression, confusion, tension, anger, fatigue, total mood disturbance, hunger, cognitive attenuation, irritability) showed a weaker response to sleep deprivation in the older group, as indicated by age*sleep deprivation interactions (ps < 0.05). The results show that older adults are emotionally less affected by sleep deprivation than young adults. This tolerance was mainly related to an attenuated increase in negative mood. This could possibly be related to the well‐known positivity effect, which suggests that older adults prioritize regulating their emotions to optimize well‐being. The results also highlight that caution is warranted when generalizing results from sleep deprivation studies across the adult lifespan.

Background: Older adults perform better in tasks which include positive stimuli, referred to as the positivity effect. However, recent research suggests that the positivity effect could be attenuated when additional challenges such as stress or cognitive demands are introduced. Moreover, it is well established that older adults are relatively resilient to many of the adverse effects of sleep deprivation. Our aim was to investigate if the positivity effect in older adults is affected by one night of total sleep deprivation using an emotional working memory task.

Methods: A healthy sample of 48 older adults (60-72 years) was either sleep deprived for one night (n = 24) or had a normal night's sleep (n = 24). They performed an emotional working memory n-back (n = 1 and 3) task containing positive, negative and neutral pictures.

Results: Performance in terms of accuracy and reaction times was best for positive stimuli and worst for negative stimuli. This positivity effect was not altered by sleep deprivation. Results also showed that, despite significantly increased sleepiness, there was no effect of sleep deprivation on working memory performance. A working memory load x valence interaction on the reaction times revealed that the beneficial effect of positive stimuli was only present in the 1-back condition.

Conclusion: While the positivity effect and general working memory abilities in older adults are intact after one night of sleep deprivation, increased cognitive demand attenuates the positivity effect on working memory speed.

Sleep loss and psychosocial stress often co-occur in today’s society, but there is limited knowledge on the combined effects. Therefore, this experimental study investigated whether one night of sleep deprivation affects the response to a psychosocial challenge. A second aim was to examine if older adults, who may be less affected by both sleep deprivation and stress, react differently than young adults. 124 young (18–30 years) and 94 older (60–72 years) healthy adults participated in one of four conditions: i. normal night sleep & Placebo-Trier Social Stress Test (TSST), ii. normal night sleep & Trier Social Stress Test, iii. sleep deprivation & Placebo-TSST, iv. sleep deprivation & TSST. Subjective stress ratings, heart rate variability (HRV), salivary alpha amylase (sAA) and cortisol were measured throughout the protocol. At the baseline pre-stress measurement, salivary cortisol and subjective stress values were higher in sleep deprived than in rested participants. However, the reactivity to and recovery from the TSST was not significantly different after sleep deprivation for any of the outcome measures. Older adults showed higher subjective stress, higher sAA and lower HRV at baseline, indicating increased basal autonomic activity. Cortisol trajectories and HRV slightly differed in older adults compared with younger adults (regardless of the TSST). Moreover, age did not moderate the effect of sleep deprivation. Taken together, the results show increased stress levels after sleep deprivation, but do not confirm the assumption that one night of sleep deprivation increases the responsivity to an acute psychosocial challenge.

Introduction: Mind wandering, the drift of attention from the current task at hand to self-generated thought is commonly associated with poorer performance, and could be a potential pathway through which sleep deprivation affects performance. Little is known about this, however. Therefore, the aim of the present study was to address the effect of sleep deprivation on mind wandering and performance in a sustained attention task. In addition, we studied age as moderating factor, since older individuals are generally less prone to mind wandering.

Materials and methods: Healthy young (18-30years) and older (60-72years) subjects participated in either a normal night sleep (NSD) or a total sleep deprivation (SD) condition, i.e. 4 conditions: NSD (n=31), SD (n=30), NSDold (n = 24), SDold (n= 24). Performance was measured using the Sustained Attention to Response Task, during which 10 thought probes were included that prompted the subjects to answer a question on what they were you just thinking about, using predefined answer alternatives. Mind wandering was quantified as occurrence of task-unrelated thoughts.

Results: Applying a 2 (age) X 2 (sleep deprivation) ANOVA, significant main effects for sleep deprivation and age were observed for omissions, indicating worse performance after sleep deprivation and in young participants (p's < .05). These main effects were dominated by an age*sleep deprivation interaction (p = .04), which was due to sleep deprivation causing significantly more omission errors in young subjects (Mean ±SEM; NSD: 2.3 ±0.9; SD: 13.1 ±4.1) but not in older subjects (NSDold: 1.9 ±0.4; SDold: 2.8 ±0.9).

Likewise, main and interaction effects for age and sleep deprivation were significant for task-unrelated thoughts (p's < 0.01). Task unrelated thoughts were significantly more frequent after sleep loss in young (NSD: 1.5 ±0.2; SD: 4.3 ±0.6), but not older subjects (NSDold: 0.3 ±0.2; SDold: 0.5 ±0.2) (interaction age*sleep deprivation p < .01). Young subjects had significantly more task-unrelated thoughts than older, regardless of sleep condition.

Task-unrelated thoughts correlated with errors of omission (r = 0.65, p < .001). Also, including task unrelated thoughts as covariate in the age * sleep deprivation ANOVA, main and interactions effect of age and sleep deprivation were no longer significant.

Reaction time was significantly slower in older adults, but no main or interaction effect of sleep deprivation occurred. Errors of commission were not affected by condition.

Conclusions: The results show that sleep deprivation caused both mind wandering and poorer task performance in young but not older participants. In addition, mind wandering rates correlated with errors of omission, which may indicate that a diminished ability to shut down off-task thoughts after sleep deprivation could be an important pathway to performance decrements after sleep loss. In line with previous research, mind wandering appears to occur less frequently in older individuals compared with younger. This lower occurrence of mind wandering in older subjects may potentially enable them to better maintain performance after sleep deprivation and partially explain the higher resilience of older adults to sleep deprivation.

Introduction: Even though the occurrence of sleep problems increases with age, few studies have focused on the cognitive effects of acute sleep deprivation in elderly. Most previous research indicate that, compared to young, older adults show less impairment in e.g. attention after sleep deprivation. However, little is known of whether the same pattern holds for higher cognitive functions. In addition, while old age is usually related to a general decrease in working memory abilities, performance on working memory tasks may differ depending on the emotional valence of the stimuli, where positive stimuli seem to be beneficial for working memory performance in older adults. The aim of the present study was to investigate the effect of sleep deprivation on emotional working memory in older adults using two levels of working memory load.

Materials and methods: A healthy sample of 48 old adults (M_Age=66.69 years, SD_Age=3.44 years) was randomized into a total sleep deprivation group (TSD; n=24) or a sleep control group (SC; n=24). They performed a working memory task (n-back) containing positive, negative and neutral pictures in a low (1-back) and a high (3-back) working memory load condition. Performance was measured as Accuracy (d'), Omissions and Reaction Time (RT).

Results: For the d' and Omissions we performed two separate 2x2x3 (sleep, working memory load, valence) repeated measures analyses of variance (rmANOVA). For the RTs, we applied a mixed-effects model. For both d' and RT we found no effect of sleep deprivation (Ps > .05). For valence, we found main effects on both d' (F_1,46 = 5.56, P=.005) and RT (F_1,95.7 = 4.84, P=.01). d' did not differ for positive and neutral pictures, but was in both cases significantly better than for negative pictures. RTs were significantly faster for positive pictures. However, a working memory load^∗valence interaction (F_1,95.7 = 4.50, P=.01) further revealed an effect of valence in the low, but not in the high load condition. In the low load condition, RTs were faster for positive than for neutral pictures and faster for neutral than for negative pictures. There was no significant effect of Omissions.

Conclusions: Our results showed that emotional working memory performance was not significantly affected by one night of sleep deprivation in older adults, which contrast what we found in a sample of young adults from the same project. In line with previous research, our results indicate a beneficial effect of positive stimuli on working memory in older adults. This effect was present in both groups and most pronounced for reaction times in the condition with a lower cognitive demand. We can conclude that, among older adults, the working memory performance is not impaired by sleep deprivation and that the benefits of positive stimuli on working memory seem intact. These findings contribute to a better understanding of older adults' cognitive functioning after sleep deprivation.

Objectives: Emotional stimuli differently affect working memory (WM) performance. As sleep deprivation has a known impact on both emotion and WM our aim was to investigate how one night without sleep affects emotional WM performance. Methods: Healthy subjects (n = 56; age 18–30 years) were randomized to a total sleep deprivation (TSD) or a rested control (RC) condition. Subjects rated their affective state and performed a 1 and a 3-back WM task consisting of neutral, positive and negative pictures at 3 pm or 6 pm (balanced) the day after sleep manipulation. Accuracy (d’) and target response time (RT) were used as outcomes. Results: In the TSD condition, subjects rated themselves as less positive (P = 0.006) but not more negative than in the RC condition. In the WM task, TSD had a detrimental effect on accuracy (P = 0.03) regardless of difficulty. Moreover, accuracy was higher in the 1-back than in the 3-back (P < 0.001) and higher for neutral compared to both negative and positive stimuli (Ps < 0.05). RT was faster for positive compared to negative and neutral stimuli (Ps < 0.05). The latter effect was particularly pronounced in the TSD condition as shown by a condition*valence interaction (P < 0.03). Conclusions: One night of total sleep loss impaired emotional WM accuracy. Noticeable, RT was faster for positive stimuli compared to negative and neutral stimuli. This effect was particularly pronounced after sleep loss. This suggests that sleep loss strengthens the opposing effects of positive and negative stimuli on WM performance, possibly due to increased emotion reactivity.