Q: Is this related to non-REM stage 1 sleep, when you may not be aware that you’re asleep?
A: No. I’m talking about people who come into the sleep lab for an overnight study and get hooked up. And in the morning, they’ll tell the tech I was awake all night, but the tech will see that their sleep was just fine.
There is a disconnect between how people perceive their sleep and how they actually sleep. For most people it’s impossible to be completely accurate to know how much you’re sleeping. Then there are some people who perceive it very differently.
Sleep trackers don’t have the level of detail of sleep studies that use scalp electrodes. When we get into the details of sleep measurement, we’re measuring 30-second epochs (sampling periods), where we look at broad measures of electrical activity. There is even more detail there that can be pulled out using other techniques, such as analyzing the spectrum of the EEG. For example, some studies have found a beta frequency in the EEG of people with insomnia, so even though they are sleeping, they often feel awake.
Basically, the subjective experience of sleep somewhat overlaps with the objective recording of what’s happening on a sleep study, but not completely.
Q: You said that first thing in the morning might not be the best time to assess your sleep – if you wake up groggy and are already thinking, “The day is shot.”
A: In general, people really feel worst in the morning. Their circadian drive is low, especially if they’re a little sleep deprived. You shouldn’t judge the day on the first hour after waking – most people are pretty cognitively impaired. I tell people they need some boot-up time.
You feel differently as the day goes on and even at different points of the day. There’s a lull in the early afternoon because of your circadian dip and then we get a second wind in the evening. How you feel isn’t one flat line; it’s really a rhythm throughout the day
Q: Would you say that consumer sleep trackers are okay for individuals to use to see a pattern but are maybe not accurate enough to use more globally in research?
A: I think there is a huge opportunity to understand sleep at a population level. For example, if there’s been a hurricane or an earthquake or Superbowl Sunday, companies have an opportunity to look at the impact – say, daylight saving time and how it affects sleep across different countries, or men vs. women, or different age groups.
There was a paper about sleep among hospital workers in Wuhan during the outbreak of the pandemic. That was a creative use of wearable devices to look at sleep in a large population.
Now, of course, the devices are not given out randomly; the people who buy them are probably a little bit healthier, maybe a little bit younger – that sort of thing. It is a biased sample.