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.

Pros:
- 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.

Cons:
- 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.
Pros:
- 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.

Cons:
- 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.
Pros:
- 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.

Cons:
- 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.
Pros:
- Instant. Takes no time or effort. Just constantly measure heart rate. Compute now or later, whatever.
- Objective.

Cons:
- 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.

Conclusion:
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, Boston.com will redirect you to a paywall if you have the gall to read more than a couple articles.) No thanks, Boston.com! Thanks, Readability!

EEG and sleepiness in awake people

I guess when you're sleeping, EEG readings would go along with your sleep stages. What about when you're awake, though?

Kaida et al (2007) say: increased EEG alpha activity predicts when you'll nod off. (as do self-reported sleepiness and heart rate variability)
Cajochen et al (1995) say: activity in the 6.25-9.0 Hz range (theta/low-alpha) increases as you stay up longer.
Finelli et al (2000) agree; theta activity increases as you stay awake longer, as does delta (slow-wave) in your next sleep. Delta drops off exponentially as you sleep.

So that's if you can measure your alpha activity over time. What if you only have a few minutes? The Alpha Attenuation Task looks to be the trick: measure your EEG alpha with eyes open vs. eyes closed. It looks like EEG alpha with eyes open decreases as you get sleepier, while EEG with eyes closed increases. So if your eyes open / eyes closed ratio is high, you're not very sleepy, and vice versa. The task was developed by Stampi, Stone and Michimori in 1993 (which I can't find) and studied again in 1995. They found it to correlate well with the MSLT. Alloway, Ogilvie, and Shapiro in 1997 found that it distinguishes narcoleptics from "normals". It seems to be another useful measure of "sleepiness" (as possibly distinct from wakefulness).

Åkerstedt and Gillberg (1990) give a pretty good analysis of what happens in the alpha (8-12hz) and theta (4-8hz) bands as you get subjectively sleepier: they increase, but particularly this high-theta-low-alpha range (5-9 hz). More if you're you're sitting still with your eyes open (as opposed to walking around and doing whatever). If you close your eyes while you're sitting, theta shoots way up, and 10-11hz goes down. This jives with the AAT findings: alpha jumps when you close your eyes, but only if you're not sleepy. (their 5-min eyes-closed, 2-min eyes-open EEG task has become known as the Karolinska Drowsiness Test or KDT.)

In validating the Karolinska Sleepiness Scale, Kaida et al (2006) compared it with a bunch of other measures and found it valid. Interestingly, these all showed correlations: the KSS, the VAS (another subjective sleepiness scale), the KDT and AAT (tests of alpha power with eyes open/closed), and the PVT (response-time test). Which means that the AAT/KDT correlate with both subjective scales (KSS/VAS) and response-time tests (PVT).

In summary: as you stay awake longer (and therefore get sleepier), your theta increases, alpha gets less sensitive to you closing your eyes, subjective sleepiness increases, and task performance goes down.
Other side notes:
- you can run a KDT in 7 minutes, and an AAT in 8 (I think I saw that somewhere). Can you maybe run it in 1 minute? 2 minutes? Or maybe you could just test their theta output for 1 minute?
- Or maybe it'd be possible nowadays to have an office worker or someone just keep an EEG by their desk and test themselves (for 8 minutes) every so often.
- I keep trying to integrate all this with my brewing 2-drive idea, where there's one drive that makes you sleepier and one that makes you more awake, and everyone just keeps talking about the sleep drive when the wake drive needs some research too. It's hard to do.

EEG 101

I've got this EEG. It tells me gamma/beta/alpha/theta/delta readings. I think learning more about EEGs and the corresponding greek lettered names would be useful.

First of all, what are these? My understanding: your brain gives off electrical impulses in regular wavey patterns. We classify these waves based on their frequency. (I think EEG folks don't talk much about "where" the wave occurs because you don't get much spatial resolution. You just know "there's 20hz going on in your brain as a whole." Seems weird! Wouldn't a 20hz wave in lobe A be potentially way different than in lobe B? Dealing without spatial resolution seems like trying to decide what to wear tomorrow when you only have a national weather report. "There's rain somewhere!" But that's all we get.)
Gamma waves (30-100hz) are really quite interesting! There's evidence that they point to the origination of consciousness itself (whatever that means) or the Binding Problem (whatever that means) or at least transcendental states in expert Tibetan meditators (whatever that means). Well! Okay, so this is super interesting but not as well understood; let's move on to waves that we know more about:
Beta waves (12-30hz) are common when you're awake, particularly when you're alert, jumpy, anxious.
Alpha waves (8-12hz) are common when you're awake and relaxed, calm, peaceful, and creative, or when you're REM sleeping.
Theta waves (4-7hz) happen when you're drowsy, sleeping (not super deep), or meditative.
Delta waves (0-4hz) are deep sleep waves.

People sometimes call the deeper, slower states "synchronized" and the shallower, faster states "desynchronized".

For a discussion of what parts of the brain cause different brain wave frequencies in sleep, this Scholarpedia article on the neurobiology of sleep and wakefulness has been pretty helpful (though also pretty dense). I don't think I'll rehash this here; it seems not super critical to me now.

I think I'll follow up with another post talking about EEGs and sleep, because that alone could fill a bookshelf.

A couple other notes/thoughts I want to jot down here so I don't forget:
- According to Wikipedia, Zen meditators produce more alpha waves. A little googling reveals a page about a study. The study is... just a citation? I don't know where the full text is. There seem to be a few papers about meditation and EEGs, like this and this, which I haven't read yet.
- Ole Jensen says: alpha waves in an area indicate inhibition, gamma waves indicate engagement. (this hypothesis is also right on his group's front page.) Their group uses MEG, which offers more spatial localization. (MEG is also more expensive and large.)
- What could this mean? There seem to be all kinds of parallels here. Zen meditation -> concentration -> alpha waves, Tibetan meditation -> mindfulness -> gamma waves? I think it is important not to get too carried away jumping to conclusions. But it's interesting!

Measuring my own focus and productivity

(Not quite inspired by xkcd today, but it's topical.)

The freedom of the researchey life is a blessing and a curse, and the difference between success and failure is likely the ability to stay on target.

How can I keep myself on target? How can I even know if I'm on target?

I was inspired by Robin Barooah, who found out that he concentrated no less (and probably more) after he stopped drinking coffee. More interestingly, he quantified concentration: every 25 minutes, if he had concentrated for 25 minutes, he marks an X. Then he was able to improve it by trying something and seeing that it correlated with more concentration. (actually, by looking through his history to see that it correlated with more concentration.)

So what will I try? A few options:

1. The very rigidly scheduled day I was trying. I think this will not work; it was hard to squeeze into my day. And it was prescriptive; it made me feel guilty about chunks I missed.

2. Forget it! Just work! I think this will not work either, because my research is on a computer, so the distracting internet is always around the corner. Also, I'm unfocused enough right now that I could just read things forever and not converge.

3. Something in between: Pomodoro. I've tried this at Google with mixed success, ultimately abandoning it. But maybe it's worth another try. It's nice that it's descriptive and works in 25-minute chunks, instead of 90-minute. It's hard to find 90 unbroken minutes, and it's nice that, if something comes up and interrupts me, I could just skip this chunk, lose 25 minutes, and keep trucking.

Sleep debt?

The idea of Sleep Debt is that each person has a "sleep quota" (an amount that he/she is supposed to sleep). If you sleep less than your sleep quota, you'll feel crummy until you sleep more to pay it back. I guess there are a few variants of Sleep Debt theory:
1. It's a straight balance. If your quota is 8 hours, and you sleep 7 hours for 10 days, you'll have 10 hours to pay back, and you won't feel good until you sleep 9 hours for 10 days (or 10 hours for 5 days, or whatever).
2. Sleep debt exists, but it's not a straight balance; a couple days of sleep-as-long-as-you-want will cure you.
3. There is no sleep debt, only REM sleep debt.
4. It's a myth. (tiredness might be caused by too little sleep, but it might equally be caused by boredom or whatever.)

There seem to be variations of Sleep Quota theory too:
1. We all have about the same sleep quota, and it's always been the same.
2. We all have about the same sleep quota, and it's changed in modern times.
3. We all have different sleep quotas.

I'm skimming abstracts here, because I'd like to externalize some thoughts and move on.
Klerman and Dijk, 2005, argue that sleep debt exists, that it persists at least over 3 days, and that our sleep quotas are about the same.
Sallinen et al, 2008, found that one night isn't enough to recover back to normal from sleep deprivation.
Wehr et al, 1993, found that long nights led to longer sleep, over a long duration of time. They did have a short bump to 10 or 11 hours before evening out to about 8, which does support the "sleep debt that fixes quickly". (see fig. 10 here, if you can)
Carskadon and Dement, 1981, agree. One night's rest returns you to baseline. (Dement gave a tech talk at Google a couple years ago; long and not worth watching.
Dinges et al, 1997, show that sleep debt does accumulate, without reaching an asymptote.
Randy Gardner stayed awake for 11 days, slept 14 hours, stayed awake 24 hours, and slept 8 hours and was fine. (okay, sample size of 1. whatever.)

Hmm. The more I read, the more it looks like sleep debt accumulates until you get a chance to sleep it off, and a few days' worth of long sleep cures you. And it's frustratingly unknown what exactly the equation looks like. As for whether we all need the same amount of sleep or not, who knows?

Well, this has been pretty frustrating. Back to your regularly scheduled "actually learning actually useful things" another day, I guess.

This research: now on Twitter.

I think this is not a terrible idea. Follow me on twitter at @dantasse, and you'll get... links to this blog's posts.

Why? So that if someone wants to know what I'm researching without reading long blogs, they can get a title blast in three seconds. And if someone wants to find me and say "I'm researching that too" or "I already did that", they'll have an easy no-pressure way to contact me.

And in the perfect future, when I become a creature of pure idea slinging, I'll be already jacked in to this twitter web. When my colleagues and I are just full of such brilliance that we can only speak in 140 characters because otherwise we'll get too many new ideas to write them all down, we'll have an outlet.

Biphasic/Segmented sleep

I was rather intrigued/distracted by this the other day.

The hypothesis is: back in the day (up to the industrial revolution), humans used to sleep in two phases. Assuming the sun sets at 8pm and rises at 6am, cavemen would sleep 8pm-midnight, wake up midnight-2am, and sleep 2am-6am. This midnight awake time could be used for reading, praying, sex, or just sitting around.

The Ted talk by Jessa Gamble started this whole thing after a coworker (co-researcher? colleague? these terms all sound so 1800's) sent it to me. (4 min; probably worth watching, for her descriptions of extreme wakefulness in people who tried biphasic sleep)

I went on to read this paper by AR Ekirch in which he gives a lot of evidence for biphasic sleep in premodern times. It's all a bit circumstantial, because they weren't exactly running controlled studies back then. But then a guy named Thomas Wehr ran a study where people were in darkened rooms for 14 hours/day and they started sleeping 8 hours in 2 phases. It got picked up by the NY Times in 1995 and then... forgotten? It's cited (only) 23 times in Google scholar.

Today a search for "biphasic sleep" reveals that it's hit a lot of internet lifestyle-design or primal something or pop-sci blogs, but that they all eventually just cite Wehr and Ekirch. Mary Carskadon doesn't dismiss it, but she hasn't researched it herself. (oh, if you're googling: another term is "segmented sleep.")

Otherwise, it seems to have been lost in history! Mollicone et al 2008 found that split sleep schedules don't positively or negatively affect PVT or subjective sleep scores, but that's about it. Hmm. Gamble is publishing a book about this, but I'm not sure when it's coming out.

My thoughts about this are:
1. I want to study this more!
2. Well, studying the health phenomenon (what happens if you segmented sleep?) is more suited to sleep researchers doing big medical studies. Ugh.
3. However, it'd be sweet if some technology we make could let everyone experiment on themselves.

Reading machine. Especially about PVT studies.

Been reading a lot of papers. Here is a thing I'd be interested to know: academic folks, when reading academic papers, how fast do you read them? I've done 4 so far today, total of about 55 pages, but there are days I've knocked out 8. I guess it all depends on the paper: some of these are easy reading because they're grounded in reality and not mathy. Probably also depends on how well you need to know it: some papers I skim because I think I won't be able to use it for much, but I just want to get the general idea.

Anyway! What am I reading about? Mostly still "how to tell how awake or sleepy you are." The PVT (Psychomotor Vigilance Test) has caught my attention. It's pretty simple: when you see a signal, press a button. The signal happens randomly every 2-10 seconds for 20 minutes. This tells some measure of "how sleepy" you are.

Here's a long book chapter about it. In short:

- it's easy to learn (after 1-3 trials, you're as good at it as you'll ever be, so no need to worry about learning effects) and easy to do
- it gets a lot of data
- it's reliable within each person
- it reflects some real brain function loss

Why it's interesting to me:

- nowadays, with smart phones, it could potentially be used by an average person to test his/her wakefulness at any time. Indeed, it has been implemented on Palm devices in 2005, and is being implemented at Intel on Android (I'm assuming. Search for "PVT" in that doc. Those look like Nexuses One, no?)

- it measures attention. (for some value of "attention"... hope I'm not totally squashing together meanings of "attention" here.) This sounds like a link between sleep and attention. Because (as I like to say) your attention is your life, that means more sleep = more attention = more life.

Other things:

- self-reported sleepiness has 2 or 3 parts: how tired you feel, and how likely you are to fall asleep. (kinda interesting correlations there: women and young people feel more tired, men and old people are more likely to fall asleep.)

- instead of the SSS, you could try this 13-item "VAS-F" visual self-reported sleepiness test. They showed that it correlates with the SSS and parts of the POMS (mood test), but I didn't see any reason to use it over the SSS, besides hand-wavey "one-item tests are unreliable" arguments. Interestingly, though, they too split this into two parts: fatigue and vigor.

A conclusion that's brewing in my head:

There are roughly 2 things to measure: let's call them the "sleep drive" and the "wake drive". They're different. When I say "how tired are you?" that's a measure of your wake drive. (It's pretty easy to manipulate that one: drink coffee or get surprised. Or get bored.) Your sleep drive is homeostatic and circadian: sleepdrive = time you've been awake * N + sin(time of day). When you try to fall asleep, that's a measure of your sleep drive minus your wake drive. And your wake drive becomes more erratic: now it's on, now it's off.

Just conjecture for now, but it fits pretty nicely with all of these studies. If it's true at all, though, where does that leave us? Can we measure sleep drive AND wake drive quickly on your cell phone? OR: can we assume sleep drive grows according to time of day (and how long you've been awake) and just measure wake drive? Hmm...

EDIT: check it out shut up, here is the coolest PVT paper! Meditation improves your PVT times. Whoa. Not expecting that. Also, experienced meditators in India can sleep a lot less.