Using your circadian rhythm, part 1

The master planner of sleep and activity is the suprachiasmatic nucleus, also know by as the "body clock". The signals produced by the body clock are referred to collectively as our circadian rhythm. Our body clock is not a natural 24 hour clock, and uses sunlight and darkness to stay in sync with the solar day. The rise of sleep disorder may be linked to the fact that many americans receive less than 10 minutes sunlight a day, and the body clock becomes out of step with the standard day.

The suprachiasmatic nucleus does not use the rods and cones in your eyes, but a third photoreceptor called the melanopsin. This protein detects changes in light intensity - it receives a strong signal when it gets brighter in the morning and darker in the evening. It is also triggered by the changing light of shadows in bright daylight. The contrast with electric light is not high enough, but the difference between bright daylight (100,000 lux) and shadow (1,000 lux) keeps the melanopsin active, and in turn, keeps us alert.

466 nm wavelength light

Melanopsin respond to a narrow bandwidth of light, in the range of 466-477nm, which explains why full-wavelength light therapy has not been very successful. It also explains why it is so easy to feel energized on a day with a bright blue sky and so easy to feel tired on a grey, overcast day.

So the melanopsin act as our day length regulators. Morning daylight signals our body clock to start its active cycle. Sunlight is strong enough to start this effect even with our eyes closed. The suprachiasmatic nucleus releases a number of hormones including serotonin, adrenalin and cortisol. The increase in serotonin helps us to become conscious again after sleep. Adrenalin and cortisol create increased metabolism and body temperature. 

By mid afternoon, the body's metabolism has peaked. There is a drop in cortisol that is apparently the signal for a mid afternoon nap. We are biologically programmed to take a nap during middle of the afternoon, roughly between 1 and 4 pm. We all know that time of day tends to be drowsy, but despite urban myth it is not because of too-warm offices or heavy mid-day meals (although those things certainly exacerbate the phenomenon).

Sleep hormones correlated 

with sleep need and sleep urge.

A surge in cortizol and adrenalin wake us up a short time later, and we have a few hours before the setting sun triggers our melanopsin and the body clock begins to convert the serotonin into melatonin, which in turn lowers our body temperature and creating lethargy. A few hours later, the melatonin slows down and it becomes more difficult to fall asleep. 

As far as we know, it is not possible to change our hormone production through will power. Therefor, we should use our base circadian rhythm to our advantage when we are designing a poly-phasic sleep system. The triphasic sleep schedule maps to the circadian system well in the following ways:

1) First nap at 1:30pm takes advantage of the mid-afternoon drowsiness to get a nice 80-90 minute nap.

2) The second nap at 10:30 takes advantage of the the increase in melatonin, body temperature drop, and serotonin drop to speed us to sleep.

3) The third nap at 5:00am takes advantage of the daily accumulated sleep debt to aid us going to sleep despite the lower melatonin levels. Upon awakening, the melanopsin resets our body clock, re-syncing us to the solar day.

By using your natural circadian rhythm, you have higher sleep efficiency (time and quality of sleep / number of hours in bed). You fall asleep faster, your naps are more restful, and you awake to a natural surge allowing you to start your day refreshed and alert.

Tomorrow we will talk about an added benefit of placing your naps on this rhythm.