FOCUS ON ACTA PHYSIOLOGICA
Review: Sleep in adolescent depression: physiological perspectives by Urrila et al. 2015
The teenage years are sensitive years, not only regarding bodily insecurities but also with regard to brain development. The fast changes in the teenage brain result in an increased vulnerability to disorders related to the psyche and sleep patterns: the incidence of severe psychiatric illness and insomnia increases rapidly during adolescence. However, are the sleep disturbances a result of depression or could they be a cause?
Many teenagers fight depression
It has been estimated that around 2 % of children suffer from major depression and around 5-8 % in teenagers. By their 18th year, 15-20 % will have experienced depression at some point. I find these numbers frightening and think that they should be taken very seriously.
What is sleep?
Sleep is a quite weird thing when one thinks of it: we lie down, close our eyes, and are virtually unconscious for 8 hours (5 hours if you are a single academic mum, and 12 hours if you are a single academic mum on holiday without the Spawn).
Sleep is universal for all animals and is frankly not fully understood, but it has a fundamental role in the maintenance of cognitive, somatic (bodily) and psychological processes. Well, who has not noted the detrimental effects of too little sleep? Too little sleep makes one stupid, perceptive to infection and emotionally unstable.
How do we measure sleep?
To measure the quality of sleep, polysomnographic (PSG) records can be used. With PSG, the different (human) sleep-phases can be detected: rapid eye movement (REM) and non-rapid eye movement (non-REM) sleep. Other ways to measure sleep are simple questionnaires and small, portable devices called actigraphs that measure the activity of the individual over the day, but without giving any information regarding the sleep phases.
The teenager-brain and sleep
I remember those terrible years when school started way too early and I recall the numbing tiredness that clogged my the brain until around 6 p.m. when suddenly the world went from monochrome to Technicolor: I was extremely awake and active in the evening and could rarely sleep until far into the night.
A surprising find (for me, at least) is that total sleep time decreases during the teens. Sleep also becomes lighter, and the circadian rhythm is shifted towards later hours simultaneously as the daytime sleepiness increases. Also, changes in REM sleep patterns have been observed. The changes in sleep patterns had an earlier onset in girls than in boys (because girl’s brains mature earlier than boy’s brains).
Sleep disturbance and depressive disorders – a chicken-and-egg situation?
Often lack of sleep or too much sleep is used to help diagnose depressions. Not long ago, sleep was seen as a cause of depression, but this simplistic view has changed over the past years to a intimate bidirectional relationship between the depression and the sleep behavior: just as much as sleep disturbances can be a sign of depression, the sleep disturbance itself might actually cause depression. Several epidemiological studies involving thousands of adolescents have shown that sleep disturbances commonly precedes depression. 60-90 % of the teenagers who had been diagnosed with depression complained of disturbed sleep. It is therefore not a situation of chicken-or-egg, but of chicken-and-egg.
Several different medical interventions have been suggested, but research is lacking for adolescents. Further research into this might save many people from much suffering. I think it is time to start taking the teenagers seriously.
Brain maturation and sex hormones
Sleep is a complex process not only reflecting the maturation of the brain but involves processes of the central nervous system. Slow wave (delta) activity (SWA) decrease significantly during the teenage years and since SWA has been shown to have a potential in shaping neural networks (SWA increases after having learned a new task), it is understandable that the researchers found that deprivation of these slow waves during sleep hampers overnight learning.
A decrease in SWA during the teens lead to a downscaling of the synapses formed, and this brain-remodeling might be very sensitive to lack of sleep, thus increasing the risk of psychiatric disorders developing.
The biological background of the sleep pattern changes during puberty is a combination of circadian clocks and the suprachiasmatic nucleus (SCN) in the brain control the pubertal development, but there is also a feedback system in place were the gonadal (sex) hormones affect the SCN either directly, or indirectly.
[Tweet “Are sleep disturbances a result of depression or could they be a cause? Or both?”]
This part of a series of article-highlights from the high ranking peer-reviewed scientific journal Acta Physiologica (impact factor 4.38).