Irritability, anxiety and flattened mood
A common research finding is that next-day emotional functioning is compromised if one has not obtained adequate sleep the night before. You may well have found yourself 'snapping' at a friend or colleague, or becoming easily irritated after a poor night of sleep. This change in emotional stability is consistently found in those who have been experimentally sleep-deprived, and in those with chronic sleep disorders. The recent Great British Sleep Survey (GBSS), found that flattened mood was the second most frequently reported daytime consequence of chronic poor sleep. Healthy participants who have been sleep-deprived also show reductions in next-day positive mood. Following healthy older adults, over several days, it was found that greater wake time during the night and poorer ratings of sleep quality were associated with reductions in next-day positive mood and increases in next-day negative mood (McCrae et al., 2008).
It is also the case that poor sleep is more frequently found in disorders that are characterized by problems with regulating emotion (e.g. depression, anxiety). This led to the traditional view that insomnia was simply a consequence of the so-called 'primary' (usually psychiatric) problem. However, research has shown that sleep-restricted healthy subjects, as well as patients free from psychiatric illness, but with chronic sleep disturbance, also show impairments in emotional well-being. This suggests a possible primary role for sleep in regulating next-day emotional responses.
An elegant example of this can be found in a recent study by a research group at the University of California, Berkeley. Here, healthy participants were split into two groups: one group viewed emotionally-arousing images in the morning and again later in the evening, each time whilst simultaneously having their brain scanned. A second group similarly viewed the images, firstly in the evening before sleep and then in the morning after sleep. Thus the main factor that differentiated the groups was that one group slept in-between testing sessions, while the other did not. It was found that in the group that slept between the two presentations of images, there was a reduction in brain activity in regions of the brain responsible for emotional processing towards emotionally arousing images, relative to the group that were awake between sessions. Moreover, the magnitude of the decrease in brain (re)activity between testing sessions, in the group that slept, was related to the amount of REM sleep-related brain activity. Changes were also found in the subjective intensity of images, indicating that those who had slept rated the images as less intense after sleep. The authors therefore concluded that sleep, in particular REM sleep, may be important in restoring next-day emotional balance (Van der helm et al., 2011).
Related to this work, researchers have questioned whether improving sleep may therefore improve aspects of mood and emotional well-being. A study published in 2008 found that improving sleep in those with depression, using CBT-I, was associated with greater depression remission rates, relative to a control group. Face-to-face CBT-I studies in those with so-called primary insomnia (free from additional medical or psychiatric problems) have similarly documented improvements in aspects of mental health and well-being. Indeed, scientific evaluation of the Sleepio course found, at two months post-treatment, that mood improved relative to a placebo group and waitlist control group.