November 11, 2008
FOLLOWING AN excellent piece on Sad by Dr Muiris Houston and a subsequent article by Catherine Foley in The Irish Times , many people have contacted me. I would like, therefore, to explain further the links between sleep, light and depression.
Sleep is essential for normal brain function where our brain, firstly, heals/ repairs itself, and, secondly, reorganises/ strengthens our memories. There are two phases – NREM (deep) sleep which deals with the first; REM (dream) sleep, which deals with the second.
In the first the brain is quiet; in the latter it bursts into activity particularly in the second half of our sleep cycle.
These bursts of REM sleep lasting about 20 minutes are when we dream. REM stands for rapid eye movements because during this phase, our eyes oscillate back and forth, ceasing when the burst of activity is over. Dreams are created by our memory box in the brain passing information over and back to parts of the brain where previous memories are stored, explaining their "jumbled nature".
The average sleep cycle is eight hours. Both phases interchange throughout the night with most REM sleep occurring in the second half. During sleep our brain secretes a neurotransmitter called melatonin (making us drowsy); generally switching off serotonin and noradrenalin systems. On waking, melatonin levels fall; and serotonin/ noradrenalin systems (making us alert) switch on again. For us to sleep at all, our serotonin system must be less active, particularly in REM sleep.
Sleep difficulties (particularly difficulty going asleep, broken sleep and early morning waking) are cardinal symptoms of depression. Many people with depression note that their mood is particularly low in the morning, improving as the day goes on. So what's happening in the brain?
In depression, the serotonin system is already underactive, partly explaining low mood. There is a much greater tendency to REM sleep when serotonin activity is particularly switched off. Normal REM/ NREM sleep patterns are disturbed, with more REM sleep than usual in the first half of the sleep cycle.
There is also a shortage of nocturnal melatonin (it is produced from serotonin), which may explain difficulties in falling/staying asleep.
Because of serotonin systems, general/nocturnal underactivity, disruption of normal NREM/REM brain activities and reduced melatonin, many with depression wake feeling very down, unrefreshed and exhausted.
If a person with depression takes a daytime nap, their serotonin system will be switched off, so they wake up more depressed.
This is problematic, since their natural behavioural pattern due to mental exhaustion is to retire to bed – worsening their symptoms. The message is clear: treat fatigue in depression with exercise, not sleep.
One of the most immediate ways to improve low mood in major depression is a single night's, total (all night) or partial (second half of night), sleep deprivation. It improves mood within hours and the effect will be increased by advancing the sleep cycle by four to six hours; but on its own it is not a realistic viable therapy. In combination with other therapies for depression, however, it does accelerate the process.
In winter, due to shortage of full spectrum daylight, serotonin activity reduces, and vice versa in summer. As a result, all of us in winter months feel "flatter", crave carbohydrates and sleep more.
Not surprisingly, due to this, 25-30 per cent of those with depression find mood deteriorating rapidly in the dark days of winter. Another special group will develop symptoms of Seasonal Affective Disorder (Sad) – depressed mood, hypersomnia and weight gain – due to a specific genetic predisposition to serotonin underactivity. It is triggered by normal winter serotonin reduction due to shortage of daylight.
One way of "fooling" the brain in both depression and Sad is light therapy on its own or through a dawn simulator.
Light therapy, particularly in the morning, increases activity in our serotonin system and is a useful adjunct to other therapies in both illnesses. Light boxes emitting 10,000 lux of light (over 20-120 minutes, depending on appliance) are recommended for routine depression.
Dawn simulator lamps fool the brain into thinking it is "summertime". All of us feel "groggy and flat" on winter mornings as the darkness increases melatonin and reduces serotonin production.
The simulator, set to come on about an hour before waking, gradually releases full-spectrum light into the room, mimicking a summer dawn. This activates a reflex between the eyes and the brain, increasing serotonin and reducing melatonin activity, so we feel less groggy and more alert.
In Sad, this boosts the serotonin system, normally very underactive in the morning. Some simulators will also include an extra light therapy attachment for those who would like to boost it further.
About 70 per cent find light therapy improves mood and other symptoms.
In severe cases this may have to be combined with modern drug therapy (SSRIs) aimed at increasing general serotonin activity.
• Dr Harry Barry is a GP based in Drogheda
© 2008 The Irish Times