Sleep has been shown to be important for a number of emotional functions. Brain correlates
to the effect of sleep deprivation on emotion have been studied in the last decades and
increased amygdala reactivity has been proposed as one possible mechanism. However,
existing literature shows inconsistent consequences of sleep loss, both in terms of behavioral
outcomes and measures of brain activity. Age is one factor that could modulate effects of
sleep deprivation on emotional functions, since both sleep patterns and emotional reactivity
change with aging. Beyond changes in amygdala reactivity, changes in the brain’s intrinsic
connectivity or immune factors could be possible mechanisms through which insufficient
sleep affects specific emotional functions as well as fatigue and sleepiness.
The aim of this thesis was to investigate mechanisms underlying effects of insufficient sleep
on emotional functions, including emotional contagion, empathy, emotional regulation, and
mood, as well as sleepiness and fatigue. The thesis consists of five studies using different
brain imaging methods and investigating both younger and older adults.
Studies I and III show that one night of restricted sleep was sufficient to cause changes in
emotional behavior, i.e. a negativity bias, negative mood, and a decreased ability to regulate
emotions (in young). However, increased amygdala reactivity was not shown to be increased
after sleep restriction. Study II shows that empathic behavior was affected in older but not in
young subjects after sleep restriction. Study IV shows that sleep restriction was associated
with increased global signal variability in the brain, as a potential marker of wake-state
instability and sleepiness. However, no significant effects on the brain’s default mode
network were found. Study V shows that patients with severe seasonal allergy had increased
fatigue, sleepiness and disturbed sleep, and signs of peripheral inflammation. However, the
study does not implicate increased translocator protein binding, as measured with positron
emission tomography, and indicating possible microglia cell activation, as involved in these
non-specific symptoms.
In conclusion, this thesis shows that restricted sleep is associated with a negativity bias and a
decreased ability to regulate emotions, at least in young. Increased global signal variability in
the brain’s gray matter could be one possible correlate to the behavioral effects of sleep
restriction. However, other brain mechanisms underlying emotional dysfunction related to
poor sleep need further investigation, using reliable methods in large samples