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- š§ Secrets of the SCN: mental health & melatonin suppression
š§ Secrets of the SCN: mental health & melatonin suppression
Kevin
February 17, 2024
This week on the Sleepstack Newsletter:
ā¢ š
How your brain reads light and how it can be detrimental to sleep
ā¢ ā ļø In the news: Government agencies accused for using light-induced sleep deprivation as a torture mechanism
ā¢ š Melatonin & mental health (a chicken and egg dilemma for sleep)
ā±ļø Your SCN: a pacemaker driven by light
What is the way to the abode of light?
And where does darkness reside?
Can you take them to their places?
Do you know the paths to their dwellings?
Somewhere deep inside the brainās hypothalamus lies a unique network of neurons responsible for some of the most powerful biological processes nature has ever produced.
The suprachiasmatic nucleus (or SCN) is a bundle of nerve cells responsible for mediating the human circadian rhythm - the biological clock programmed into every single cell in the human body. Scientists call the SCN the ā24-hour pacemakerā of the body. But what makes this āmaster clockā tick?
Koch, B., Nagtegaal, J., Kerkhof, G. et al. Circadian sleepāwake rhythm disturbances in end-stage renal disease. Nat Rev Nephrol 5, 407ā416 (2009)
The human circadian rhythm is mediated, to a large extent, by light that enters the eye. This light is converted to electrical signals, which are then sent directly to the SCN via the retino-hypothalamic tract.
The pineal gland, located within the brainās two hemispheres, then receives signals from the SCN to produce the sleep hormone melatonin. Regular cycles of melatonin production help maintain the bodyās sleep-wake cycle.
šØ [In the news] U.S. personnel condemned for using artificial light as a torture device
Weāve already seen that night-time lighting can compromise the circadian clock and the bodyās vital functions, starting with the sleep-wake cycle. It turns out that light-induced sleep deprivation is a proven torture mechanism!
Just ask the Physicians for Human Rights whoāve exposed how shadowy government agencies use light exposure as a torture technique. For example:
āThe systematic use of sound and light bombardment by U.S. personnel has been extensively documented. Military guards and intelligence agents have confirmed that subjecting detainees to strobe lights was regularly used in interrogation procedures at GuantĆ”namo Bay. The ICRC associated the use of constant, bright light and blaring music with sleep deprivation, and condemned the sensory assault allegedly inflicted by coalition forces in Iraq.ā
š Low melatonin levels linked to mental health disorders
Low melatonin levels and circadian-cycle disturbances have been frequently correlated with various forms of depression. e.g.
ā¢ Srinivasan et al (2006) Melatonin in mood disorders - Melatonin is a rhythm-regulating factor in the body and can be both a āstate markerā and a ātrait markerā of mood disorders.
ā¢ MA Quera Salva et al (2011) Circadian Rhythms, Melatonin and Depression - Evidence points to a role of the biological clock in the development of seasonal depression, bipolar disorders and major unipolar depressive disorder (MDD).
ā¢ Mendlewicz, J et al. (1979). Abnormal 24 hour pattern of melatonin secretion in depression - Review of existing research linking depression with abnormal melatonin secretion & low levels.
ā¢ M Crasson et al (2004) Serum melatonin and urinary 6-sulfatoxymelatonin in major depression - Found delayed melatonin secretion eg. less in evening & more in morning, but still similar total secretions.
While there is still much debate about which comes first (i.e. a chicken-or-egg causality dilemma), itās incredibly common that poor sleep and mood disorders go hand in hand.
At the core of the problem though, is a repeatedly occurring symptom: disruption of the sleep-wake cycle (yep, the one regulated by light at the SCN):
Alteration of the sleep-wake cycle and of the sleep structure are core symptoms of a major depressive episode, and occur both in course of bipolar disorder and of major depressive disorder. Many other circadian rhythms, such as the daily profiles of body temperature, cortisol, thyrotropin, prolactin, growth hormone, melatonin and excretion of various metabolites in the urine, are disrupted in depressed patients, both unipolar and bipolar individuals.
ā”ļø Recommendation zone
Actionable insight: Use your night mode!
Indoor lighting affects the timing of circadian shifts and ordinary room lighting at night, before bedtime, has been shown to halve melatonin secretion. Evening artificial light also damages cognitive performanceā .
One counter-measure is the night-mode feature now built into most smartphones and computers (e.g. Night Shift on iOS)
Or try something a bit fancier!
To really cut down on the effects of artificial light though, consider software like f.lux - which carefully changes the colour of your display to adapt to the time of day (warm at night and like sunlight during the day).
Some of the best options include f.lux (Windows / MacOS / Linux) and Twilight (Android).
My current Sleepstack:
This silk sleep mask is my favourite at the moment. (The material stays cool and doesnāt bother me during the night.)
ā¢ The human eye can detect a single photon of light in a dark room. And light affects melatonin secretion even when your eyes are shut.
ā¢ Iāve found that I wake up feeling so much more rested with a sleep mask (and itās a fraction of the price of blackout curtains)!
Thatās all for this week!
Weāll be back in your inbox on Saturday,
Kevin
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