The Importance of Sleep

It is well known that sleep is one of the most important processes that your brain undergoes. Sleep is integral to normal brain functioning, and disrupted sleep has been linked to a whole host of problems with implications in mood disruptions, mild-cognitive impairment, and mental illness. Sleep is also key to normal emotion regulation, memory consolidation and other cognitive processes. In addition, brain activities that occur during sleep, such as toxin removal, help the brain recover from the “wear and tear” of the day and help to facilitate normal neuronal communication when awake.

Neuronal communication.

Research into the relationship between sleep and depression provides support for sleep disruption as a predictor of onset of depression. Sleep impairment is one of the major debilitating symptoms of depression – so much so that it is one of the nine symptoms of Major Depressive Disorder (MDD) described in the DSM-5. Many individuals with MDD experience insomnia, hypersomnia or other sleep-related problems, with a prevalence of around 80% of depressed individuals self-reporting sleep disturbances (Armitage, 2007; Breslau et al., 1996). Generally, these sleep disruptions manifest as problems in sleep timing and coordination of non-REM and REM sleep cycles (Armitage, 2007). Analyses of sleep electroencephalography recordings show three main changes present in depressed individuals: a shortened latency to REM sleep, decreased slow wave sleep, and an increase in REM density (Steiger & Kimura, 2010; Holsboer, 2008; Modell et al., 2005; Armitage, 2007). The changes in REM density persist even after an individual successfully goes through clinical remission (Pillai, Kalmback, & Ciesla, 2011; Modell et al., 2005).

Interestingly, the EEG changes seen in depressed individuals are present in individuals with a genetic predisposition to affective disorders, prior to any disorder diagnosis. These EEG changes are stable across time and were present four years after initial EEG recordings (Modell et al., 2005; Steiger et al., 2010). These findings support the efficacy of REM sleep dysfunction as a biomarker of depression and indicate that this sleep disruption is linked to neurobiological and molecular changes in the brain.

Sleep quality is affected by our everyday activities, from our technology use to how stressed we feel throughout the day. Chronic stress has recently been linked to REM sleep dysfunction in mice, providing even more evidence for the importance of a good night’s sleep. Mice exposed to a variety of mild stressors showed a significant increase in the likelihood of developing depressive-like symptoms, of engaging in normal self-care, and of being social with other mice (Nollet et al., 2019). Upon investigation as to why these behavioral changes occurred, researchers found that these stressed mice showed an increased continuity and duration of REM sleep

Difference in REM duration (A) and REM bout length (B) in mice with mild chronic stress, in red, and normal control mice, in gray. Source: Nollet et al., 2019.

and an abnormal stress hormone regulation (Nollet et al., 2019). This influences our stress response system, the hypothalamic-pituitary-adrenal (HPA) axis, and corticosterone, one of the key stress hormones, creating an inability to deal with stress healthfully.

In addition, chronic stress impacted the transcriptome and gene expression in these mice, showing more direct changes in the hippocampus and frontal cortex (Nollet et al., 2019). This illustrates how chronic stress actually changes the brain, and that related dysfunction in sleep is important to keep track of due to links with mental illness.

To bring another piece into this puzzle, adequate sleep is especially stressed for adolescents. During this period in life, the brain is still developing, with the frontal cortex undergoing the most growth. Adolescence is also a time of seriously disrupted sleep; most adolescents need 8 or more hours to properly function but rarely get above 7 hours a night. By pairing this lack of sleep with highly stressful school and social situations, it makes sense that the adolescents are more likely to develop mental illnesses than most other age groups.

And because monitoring sleep has proven important in both understanding disorders like depression and providing novel information about genetic and neurobiological factors that influence abnormal behavioral responses, it would be beneficial to keep track of sleep habits and patterns in order to provide insight into health and wellbeing. Early identification of sleep abnormalities through sleep monitoring could allow for preventative measures to be taken. This would hopefully help identify and support adolescents who are enduring chronic stress and those who are thus at higher risk for development of disorders linked to sleep dysfunction. The importance of sleep cannot be stressed enough, so I hope you are able to get your 8+ hours of sleep tonight!

References

Armitage, R. (2007). Sleep and circadian rhythms in mood disorders. Acta Psychiatrica Scandinavica, 11(Suppl. 433), 104-115. Doi: 10.111/j.1600-0447.2007.00968.x.

Breslau, N., Roth, T., Rosenthal, L., Andreski, P. (1996). Sleep disturbance and psychiatric disorders: A longitudinal epidemiological study of young adults. Biological Psychiatry, 39(6), 411-418. Doi: 10.1016/0006-3223(95)00188-3.

Holsboer, F. (2008). How can we realize the promise of personalized antidepressant medicines?. Nature Reviews Neuroscience, 9, 638-646.

Modell, S., Ising, M., Holsboer, F., Lauer, C. J. (2005). The Munich Vulnerability Study on Affective Disorders: premorbid polysomnographic profile of affected high-risk probands. Biological Psychiatry, 58(9), 694-699. Doi: 10.1016/j.biopsych.2005.05.004.

Nollet, M., Hicks, H., McCarthy, A. P., Wu, H., Moller-Levet, C. S., Laing, E. E., Malki, K., Lawless, N., Wafford, K. A., Dijk, D., Winsky-Sommerer, R. (2019). REM sleep’s unique associations with corticosterone regulation, apoptotic pathways, and behavior in chronic stress in mice. Proceedings of the National Academy of Sciences of the United States of America 116(7), 2733-2742. https://doi.org/10.1073/pnas.1816456116.

Pillai, V., Kalmback, D. A., Ciesla, J. A. (2011). A meta-analysis of electroencephalographic sleep in depression: Evidence for genetic biomarkers. Biological Psychiatry, 70(10), 912-919. Doi: 10.1016/j.biopsych.2011.07.016. Steiger, A. & Kimura, M. (2010). Wake and sleep EEG provide biomarkers in depression. Journal of Psychiatric Research, 44(4), 242-252. Doi: 10.1016/j.jpsychires.2009.08.013.

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