1.    PROJECT AIM & DEVELOPMENT DURING THE PROJECT TIME

The main aim of the project was to investigate whether sleep deprivation affects the response to acute psychosocial stress in terms of subjective and physiological measures. In order to induce psychosocial stress, we used the Trier Social Stress Test (TSST) (Kirschbaum et al., 1993). Secondly, we were interested in studying how sleep deprivation (and acute stress) affects different aspects of attention based and higher cognitive functioning as well as mood. These research questions were addressed with an age perspective in mind, in order to create new knowledge on whether the effects of sleep deprivation and acute psychosocial stress differ in young and older adults.
Overall, the project followed the intended project plan. One protocol change comprised the control of sleep deprivation. Instead of assuring protocol compliance by actigraphy only, we monitored the subjects allocated to the sleep deprivation condition in the laboratory starting from the evening before the experiment onwards to ensure better control of the wakefulness. Moreover, we added salivary alpha amylase as additional outcome indicating autonomic activation in response to acute stress.

2.    IMPLEMENTATION

In the main data collection, 124 young (18-30 years) and 94 older (60–72 years) adults participated in one of four conditions: 1) normal night sleep, 2) normal night sleep & acute psychosocial stress, 3) sleep deprivation, 4) sleep deprivation & acute psychosocial stress. The data collection was completed in 2016. Since then we have worked on conducting data analyses, and developing scientific publications.

3.    PROJECT’S THREE MOST IMPORTANT RESULTS

a.    EFFECT OF SLEEP DEPRIVATION ON THE STRESS RESPONSE
The main aim was to study the effect of sleep deprivation on the response to acute stress. Ratings, and all physiological outcomes (cortisol, alpha amylase, heart rate variability) showed that the psychosocial stress paradigm (TSST) was successful in eliciting a stress response, which is a pre-condition to interpret the results. Sleep deprivation was associated with higher subjective stress levels and higher cortisol already at baseline before the subjects underwent the TSST. This, in line with earlier research, indicates that sleep deprivation is itself a stressor. However, sleep deprivation was not associated with a significantly different response to the TSST. Thus, against our expectation sleep deprived individuals do not seem to be more vulnerable to acute psychosocial stress. These results are nonetheless very important, not the least because recent smaller studies show heterogenous results: one reported an increased, another an attenuated cortisol response to acute stress. Our findings, which were obtained in the largest sample so far (which reduces the risk for unreliable findings), suggest that there is to date no strong support for the assumption that one night of sleep loss has a pronounced impact on the response to acute psychosocial stress in healthy individuals. Results were recently accepted for publication (Schwarz et al., 2018).

b.    EFFECT OF SLEEP DEPRIVATION ON COGNITION
The project aimed also at generating improved knowledge on which aspects of cognition are impaired by sleep loss. Using a SART task, which studies sustained attention, we found that sleep-deprived young adults were impaired compared with well-rested ones, in line with previous results. To gain better insight in what causes this impairment, we included thought probes that prompted the participants to specify whether their thoughts were focused on the task or on task-unrelated aspects (i.e. so-called mind-wandering). Our initial results indicate that mind-wandering was increased in sleep deprived young individuals (conference abstract, article in prep). Further preliminary results from a working memory task highlight that mostly attention related aspects are adversely affected by sleep deprivation while aspects relying on higher cognitive function remain more intact (Gerhardsson et al., in prep), at least in the young adult group. Finally, we also studied the interaction between emotion and cognitive processes using an emotional working memory task, which has so far been a neglected area in sleep research. The results (Gerhardsson et al., under review) suggest that accuracy was impaired in sleep deprived compared with well-rested young adults. Interestingly, speed was not impaired; in fact positive stimuli may even facilitate working memory processing speed after sleep loss.
The data we have analyzed so far lead to improved knowledge in three areas of cognition. In the future, we plan to investigate the data from additional cognitive tests, and to address which effects acute stress has on cognition.

c.    AGE DIFFERENCES
A further major aim of the project was to investigate whether young (18-30 years) and older (60-72 years) adults differ in the response to sleep deprivation and acute psychosocial stress. This creates much needed novel knowledge, as the vast majority of prior research is carried out in young adults.
We found that age did not moderate the effect of sleep deprivation on the stress response; neither young nor older adults were particularly affected by sleep loss regarding the response to acute stress. However, older adults had higher basal sympathetic activation (alpha amylase) and altered cardiac autonomic functioning (lower HRV) than young adults. Moreover, their cortisol values stayed more stable across the test session compared with young individuals, regardless of exposure to sleep deprivation and stress. Interestingly, older adults felt slightly more stressed at baseline, but the response to TSST in terms of stress ratings was less strong (Schwarz et al., 2018). The data collected in the project also allowed us to study age-dependent effects of sleep deprivation on cognition and mood. In line with previous research we found that mood is poorer in sleep deprived individuals. However, our results showed that this effect is less strong in older adults, who are more resilient in particular regarding the negative dimension of affect (Schwarz et al., submitted). Moreover, sleep deprived older adults appear to better maintain sustained attention, emotional and verbal working memory performance than young adults (Schwarz et al., in prep, Gerhardsson et al., under review, Gerhardsson et al., in prep). Thus, overall our findings highlight that effects of sleep deprivation observed in young adults cannot necessarily be generalized across the adult life span.
In summary, the study has shown that one night of sleep deprivation does not significantly affect the response to acute stress, that the emotional response of older adults to sleep deprivation is weaker than in younger age, and that older adults are cognitively less impaired by sleep deprivation and have less mind wandering after sleep deprivation than young adults.

4.    NEW RESEARCH QUESTIONS

The project has generated a number of new research questions.
A main result was that one night of sleep deprivation did not significantly change the reactivity to acute stress. This was against our expectation, but the results fit nevertheless well with previous animal research. Since animal research on the other hand suggests that repeated partial sleep deprivation may change responsivity to stress, it would be important to study this in humans. Moreover, future research needs to address whether the response when exposed to different types of stressful situations, e.g. less strong or repeated stressors is altered after sleep loss.
An interesting result of the present project is the higher occurrence of task unrelated thoughts (mind-wandering) in sleep deprived individuals. Since recent research suggests that a diminished ability to regulate mind wandering is linked to performance decrement and lower mood, future research efforts are needed to investigate in more detail which forms of mind-wandering occur in conditions of sleep loss (e.g. with or without awareness).
Our preliminary results also indicate clear differences between young and older adults in their response to sleep deprivation regarding both cognitive performance and mood. It would be interesting to follow up on these age differences, and to investigate to what extent biological mechanisms such as sleep pressure and other aspects such as strategies to deal with sleep deprivation play a role.

5.    INTERNATIONAL DIMENSION

We aim to make the results accessible at the international research front. The first article has recently been accepted in the prestigious journal Psychoneuroendocrinology (level 2 in Norwegian bibliography system). Two articles have been submitted to top journals in the sleep field (SLEEP; Journal of Sleep Research). Moreover, we organized the Symposium “Sleep less - stress more?” with international leading researchers at the European Sleep Research Society Conference (2016). Results have been presented at international conferences:
•    World Sleep Conference, Istanbul, 2015
•    European Sleep Research Society Conference, Bologna 2016
•    World Sleep Conference, Prague, 2017
•    European Sleep Research Society Conference, Basel, 2018 (upcoming)

6.    DISSEMINATION, PUBLICATIONS & PUBLICATION STRATEGY

Apart from international conferences, results have been presented in research seminars at Stockholm University and Karolinska Institute. We aim at spreading the results to other contexts (e.g. popular press, personal blogs) in the future, after findings have been published.
We intend to publish results in high-ranked international journals, which will be made accessible to the public by golden or green open access. A further aim is to publish also so-called “Null-findings” to not further contribute to publications bias, which occurs when only results in line with the hypothesis are published.

Please find a list of publications and conference contributions on the next page.