Thursday, March 31, 2011

Markers of Sleepiness (or Wakefulness)

Argh, I could read things forever! Focus. What am I looking for? A marker of wakefulness, an easily-measurable signal that tells you how awake you are.

Lengthy side note: Aeschbach et al (1997) talk about the two process model of sleep regulation in relation to EEG. Delta, theta, and low alpha waves are all controlled by a homeostatic "Process S" and a circadian "Process C". Process S makes theta and low alpha increase as you stay awake longer, then when you sleep, they decrease as delta increases. The circadian process, on the other hand, deals with aligning you to time of day. So while it's true that sleep is not a one-component construct, it may be (largely approximable by) a two-component construct, and those two components are S and C. (Therefore, surprisingly enough, I haven't developed or furthered any brilliant revolutionary new theories yet.)

So I've convinced myself that "a marker of wakefulness" and "a marker of sleepiness" are at least pretty similar, so I'm looking for a marker of sleepiness. There was apparently a whole conference about this at Harvard. Media summary here. What's the marker, and how can I help bring it to you? Particularly, how can I bring it to you in a way that lets you run all-day kind of studies?

Option 1: EEG. Put an EEG headset on someone, measure eyes-open alpha vs eyes-closed alpha for 12 minutes (Alpha Attenuation Test) or maybe just measure theta, or TLFA (theta/low-frequency alpha) for a couple minutes. Output a number, that's how sleepy you are.

- It's objective (unless you get into subjective scoring of it, but let's try not to).
- It might be quick. The AAT takes 12 minutes, the KDT takes 7. But I got the actual original AAT paper, and it turns out that they (arbitrarily?) pick 12 minutes (2 open, 2 closed, repeat 3x) but looking at their data it seems that 4 minutes would have worked well too. Maybe 2 minutes would. Who knows.
- I mean, I want this to work. EEGs are interesting.

- It might not work. James Krueger argued that EEG delta power alone is not always a satisfactory marker for sleepiness. (he then generalized to "it seems unlikely that a single EEG measure will be reliable as a marker of sleepiness for all conditions", which the media generalized to "Brainwaves? They don't correlate well to sleepiness." okay, the media can be frustrating, etc etc) I'm not convinced. There may be other ways to measure sleepiness besides just delta power.
- Existing EEG headsets are still kind of bulky. Picture big audiophile headphones. Now, unless someone's going to carry that around and whip it out every couple hours, they're not going to do this study.

Option 2: Subjective Tests. Give someone the SSS or KSS or VAS or something on their phone every couple hours.
- It's easy to implement.
- It's quick to do. (quicker than a text, and people do those all the time.)
- It uses existing phones. Or perhaps watches.
- It could be part of a bigger study.

- It's, well, subjective.
- People can forget to do it or decide not to. (even if you send them an alarm.)

Option 3: Behavioral Tests. Make someone take the PVT or something on their phone every couple hours.
- Could still be quick. Again, traditional PVT takes 5-10 minutes but maybe we could make a faster test.
- It's been used for quite a while and pretty well validated.
- It's easy to implement (I think).
- It's on that phone that you already carry around.

- Might not be quick. Maybe if you go below say 5 minutes, validity drops off.
- People can still forget to do it or decide not to.

Option 4: Biological Markers. For example, heart rate variability. As you get sleepier, your heart rate becomes more irregular.
- Instant. Takes no time or effort. Just constantly measure heart rate. Compute now or later, whatever.
- Objective.

- Can a heart rate monitor be unintrusive?
- Maybe this signal won't be as strong. I haven't read more than this paper about it.

Why not put a few of these together? You could imagine doing a subjective 1-7 scale "how awake are you?", playing the PVT game for a couple minutes, and having your heart rate recorded all at once. Then we could see if any of the ratings correlated well with sleepiness, or even if it's some combination of them.

So that's what I'm going to try to implement. This ends the "immediately relevant" part of the post; now I'll try to throw down some more thoughts about some more papers so I can find them later, and also because they're kind of cool:

Aeschbach et al (2001) offer evidence that short sleepers feel just as tired as long sleepers, they just deal with the lack of sleep better.
Harrison and Horne (1996) describe people who aren't sleep deprived or suffering from any disorders, but who can fall asleep at the drop of a proverbial hat. This seems like not news, if you imagine sleepability on a normal curve: some people just have high sleepability.
Rector, Schei, Van Dongen, Belenky, and Krueger (2009) argue that sleep is local and use-dependent. The more you use an area in waking, the more slow-wave sleep you'll get when sleeping. When some systems get tired out, they send inputs to the VLPO, which I guess shuts down when a bunch of systems shut down? And nearby systems tend to be in synch, which is why you generally don't have one arm, or just your visual cortex, falling asleep. That is... neat! And not immediately relevant to me. Sounds like if you had better spatial resolution, say on an EEG or something, you could, say, stimulate one ear a lot and then notice that the part of the brain that processes it getting more slow-wave sleep.
- Maclean, Fekken, Saskin, and Knowles (1991) did some analysis of the SSS and sleep in general. Their analysis of the SSS I am not too concerned about. Their analysis of sleepiness (that there are two components to it) is more interesting. But I'm not convinced; the second component could just be a counteracting component, or maybe it's the circadian rhythm in the two-process model.

Metablog: here's a cool new view of this blog. Thanks, Blogger!
Metablog 2: I am going to link to Readability links of articles all the damn time now. It's so good. Compare the original with the readable one. (not to mention, will redirect you to a paywall if you have the gall to read more than a couple articles.) No thanks,! Thanks, Readability!

No comments:

Post a Comment