Remember when the Russians put a bunch of people in isolation for a year and a half in 2010/2011 to see if we could handle going on a trip to Mars without going crazy? Well they’ve since completed that experiment, and the first report about altered sleep patterns has just come out in PNAS.
They measured sleep timing and quality using actigraphy, which is pretty standard way that labs (including my own) measure sleep timing and quality, and general activity. It’s basically a little wristwatch with an accelerometer in it that you wear 24/7 and measures your movements. It’s pretty accurate at measuring when you fall asleep or nap, and how many times you wake up during the night, etc. The study found that most of the “crew” members experienced more sedentary behaviour and more total sleep over the mission. In fact, sedentary behaviour increased greatly over the first 3 months, and then more gradually for the rest of the time.
In general, this increased amount of sleep over time seemed to be related to better performance over time in computerised “vigilance” tests, which measured psychomotor reactions. That’s good news for most of the crew. But the authors of this study also looked at individual differences in some of these measures. This isn’t easy to do with only six people (all males), so the results should be treated with caution. The main differences they noticed were related to sleep-wake cycles. Although their work schedules revolved around a 24-hour clock, no one was exposed to natural sunlight and the earth’s natural dark/light cycle. We know from previous studies that our natural body clocks, in the absence of light cues, are not quite 24 hours (although there might be a gender difference). But we usually stick to 24 hours due to helpful light cues. Most of the crew members in this experiment did that, too. But one crew member had a slightly extended natural cycle that increased over the mission to more than 25 hours by the end. Another one had a consistent “biphasic” sleep pattern, which means he slept at night but also had a short nap during the afternoon. What’s interesting is that these two guys were the only ones that showed a lot of trouble getting to sleep at the start of the mission – they took about 2 hours more to fall asleep for the first month than they had before the mission started.
I think it would also have been good to know if there were any significant differences between these two members and everyone else in terms of sleep quality pre-mission. Maybe they could screen astronauts before going on real missions to predict if they will experience adverse effects.
My guess is that we’ll get many more reports from this study soon, hopefully including results on mood disturbances and other physiological changes from daily blood samples, so I will be on the lookout.