Monday, December 8, 2008


Sunday 7th December

No revolutionary news from the field today. Sunday is a day of rest here, which is the perfect day to tell you about my experiment, being after all about sleep!. I measure the very willing and collaborating participants for 48 hrs in a row. They wear an actigraph bracelet for this whole period, which monitors physical activity and body temperature. In the morning and the evening -as well as once for every subject every 2 hours a day-, saliva samples are taken, with the aim of determining cortisol and melatonine levels. These two hormones provide information about the circadian rhythms, which we expect to be disturbed under the influence of the constant daylight. Indeed, participants to expeditions in the polar summer often complain about the difficulty of sleeping a whole "night" in this constant day. One of the goals of our measurements is thus to check whether the most evident hypothesis -the lack of a "go-to-bed" signal due to the lack of
external night- is indeed underlying these subjective reports. Another goal is to verify if the level of physical activity is able to counteract this sleep disturbance. The reasoning here can sound quite trivial -the more you work out, the better you sleep-, yet represents the interaction between the two "steering" mechanisms of sleep. On one hand, the circadian process, which is an expression of our internal body clock -which tells you once a day to get to sleep-, and on the other hand, the sleep homeostasis process, which is basically the sleep pressure that builds up with the time awake, and is also influenced by the type of activity during this time awake. And
this is where it becomes interesting to measure the degree of physical activity, especially since we have a wide range represented here: the "builders" have a very intense physical activity, whereas base camp duties require a lot less energy. Data from last year's expedition showed that the intensity of the physical activity was indeed related to sleep efficiency.

So this year, we want to expand the data-set with the saliva samples, mood questionnaires (to investigate whether potential sleep disturbances might have an effect on people's subjective well-being), attention tests, and a real polysomnography: this would allow for a more detailed investigation of sleep (qualification of sleep stages rather than only a recording of sleep duration).
Well, once in a while, a whole serious post can't do no harm.


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