SPOILER ALERT!
~ REM sleep is the dream stage
~ Noradrenaline is a chemical that makes us alert, attentive and ready to react.
~ During REM sleep, noradrenaline levels are at their lowest.
~ REM sleep helps us regulate our emotions, both positive and negative
~ Not enough REM sleep leads to overeating and craving for high calorie- food
~ Not enough REM is one causal factor for relapse in addiction disorders
~ Not enough REM is one causal factor for the development of anxiety disorders
A body of research has established a relationship between sleep and emotional regulation. Specifically, it has shown that sleep contributes to optimal affect regulation, which is a finding supported by the pervasive occurrence of sleep abnormalities in psychiatric disorders.
Sleep and the Brain
A typical night of sleep consists of two main parts which are REM (rapid eye movement) and non-REM sleep. The former represents the dream state (REM) and the latter corresponds to deep sleep (it is further divided into 4 stages).
Neuroimaging studies reveal that during REM sleep, the emotional centers in the brain are particularly active. These include the amygdala, the striatum, and hippocampus. Parallel to this activity is that of the insula and the medial prefrontal cortex (mPFC) whose function is to modulate the activity of the emotional centers.
In addition, the neurochemical activity in the brain during REM echoes this neural activity by showing reduced levels of noradrenaline, which is a chemical involved in mobilizing the brain and body for action. In fact, REM sleep is the only time within a 24-hour cycle during which the levels of noradrenaline are at their lowest, which is revealing since noradrenaline is associated with emotional arousal.
Effects of Sleep Loss in the Brain
This pattern of brain activity during REM sleep becomes more insightful when we look at what happens during sleep deprivation. Notably, sleep loss has always been associated with irritability and emotional volatility. For example, one night of sleep loss increases the experience of stress, anxiety and anger when facing a little bit of stress.
Furthermore, this emotional dysregulation is reflected in the brain with increased activity of the emotional centers and reduced connectivity with the regions of the mPFC. Particularly, one night of sleep loss triggers a 60% increased reactivity of the amygdala to emotionally negative stimuli (e.g., pictures depicting emotionally negative scenes like a dog attack or someone in pain, etc…).Exaggerated amygdala reactivity and reduced mPFC connectivity is also seen after 5 nights of only 4 hours of sleep.
This pattern of brain activity during sleep loss is not strictly restricted to negative emotions as it also affects positive emotions. Indeed, sleep loss is also associated with increased reactivity to emotionally positive stimuli like money and food. For example, when sleep deprived, individuals tend to display increased preference for higher calorie foods and tend to overeat. Overall, sleep loss drives the individual to overvalue rewards and underestimate losses.
Sleep Loss and Psychopathology
Taken together, sleep loss is associated with exaggerated responses from the emotional centers to both positive and negative emotional stimuli along with under-activity in the mPFC, which would normally put a brake on their activity. The resulting behavior is characterized by emotional volatility along with increased anticipatory reactions for both positive and negative stimuli.
For example, when anticipating a negative event, sleep deprived participants with high trait -anxiety (i.e., refers to people who tend to be anxious easily without necessarily suffering from an anxiety disorder) experience severe anticipatory anxiety. Unfortunately, this pattern of reactivity puts them at risk for developing an anxiety disorder.
Similarly, high anticipatory reaction to positive stimuli is a characteristic behavior among gamblers and addicts. Particularly interesting is the fact that sleep loss is also a hallmark of addiction, and it is a reliable predictor of relapse in several addiction disorders.
Reference:
Goldstein, A. N., & Walker, M. P. (2014). The role of sleep in emotional brain function. Annual review of clinical psychology, 10, 679–708. https://doi.org/10.1146/annurev-clinpsy-032813-153716