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.