Big ideas in sleep: Borbély's Two Process Model

I think I'm sticking with sleep for now. I enjoy it, and I'm familiar with the literature a little better than other sub-fields. I may even try to volunteer in a sleep/circ lab the following semesters(!). In any case, I won't pretend to be an expert either... Definitely not, and I really don't want to step on anyone's toes. But sleep is FUN for me, so that's what I'm doing. For now. Unless I find another hobby. Undergraduates are allowed to do that, right?

ON TO THE PAPER!

We've got lined up for you one of the biggest, bestest papers in sleep research ever published - or at least I think so anyway - and it's pretty easy to find a .pdf even without a subscription to a journal service, because tons of courses have used this paper as part of their required readings.


Borbély, A., & Achermann, P. (1999). Sleep Homeostasis and Models of Sleep Regulation Journal of Biological Rhythms, 14 (6), 559-570 DOI: 10.1177/074873099129000894



Now, to make this clear, Borbély wasn't unveiling this model with this paper - he had worked on it long before, and this particular paper is among the long line of papers on the model. This one, though, is a well-consolidated version of the work.

So to make clear definitions: we're saying that sleep regulation is homeostatic in the sense that there is a baseline measure of some sort, and the organism exhibits a "pressure" to return to that baseline. What's being measured in the baseline in the case of sleep will soon be apparent.

This is what sleep looks like:



The top chart shows stages of sleep over time, from wake, to stages 1-4 and REM sleep. Keep in mind here, all this stuff has been common knowledge for a while - early on, sleep goes through the stages, from shallow to deep; most of the deep sleep is in the early part of the bout, whereas REM starts to happen in 90-120 minute epicycles (ultradian cycles) later in the bout.

The bottom chart is where the interesting stuff for Borbély is, mostly - the frequency of slow wave oscillations throughout the night. (If you've ever seen a sleep study, this is what they're looking at with the EEG-cap). Slow wave oscillations are strongest in the deeper stages of sleep (3 & 4), hence their name as "slow wave sleep" - REM lacks slow wave activity altogether.



This is again more evidence showing slow wave density - a spectral power density graph. The baseline (the perfectly straight horizontal line) on the left is the fourth cycle of sleep. Basically, what's going on here is showing that there's more slow wave activity earlier in sleep - inferable from the previous image - and that slow wave activity drops off and is less dense later in the sleep bout.

The right side shows averages across whole nights, with 40 hours of sleep deprivation and the following three bouts of sleep. The baseline is the third night, and the point here is just greater density in the night(s) immediately following the deprivation.

So for the homeostatic model - we see that deprivation drives up slow wave density. And further, we see that slow wave density is highest earlier in the night. So we have the suggestion that we can measure sleep "pressure" by the density of this slow wave activity. A few more figures cover this in detail (and I thoroughly encourage anyone interested to read the full paper), but basically longer sleep debt increases slow wave density - continued sleep drives it down.

Glancing over a lot of interesting research, but to get to the important point of it all, we have the point that sleep is homeostatically regulated. But there's another factor, and this one I'm not going to cover quite as thoroughly, because many before me have done it much better. Circacian processes are the cyclic processes with a period of about 24 hours, give or take a little bit of variation. Circadian processes are also important in sleep/wake, and part of Borbély's insight is working this well into the mix.



This, in essence, is Borbély's two-process model. Process S is the aforementioned sleep process - the tendency of slow wave activity to build up over the night, and drop off. There's a cool bit of math there in the drop-off during sleep (the hashed out area) - it's a logrithmic cliff (if I'm not mistaken), so similar in structure to, say, Newton's Law of Cooling for any physicists or chemists out there - the higher the starting point, the faster it drops. Process C is the circadian process, with the bar under the chart showing time of day in a 24 hour cycle. The distance between the S and C lines is the pressure for the organism to sleep - explaining, in a sort, why you're a little less tired mid-day after a marathon wake session, even going longer without sleep. [I just edited this to fix it - I mistakenly noted that the distance was indicative of slow wave density, which is actually JUST associated with Process S. Forgive my late night typing errors.]

This paper does throw out a couple of nice little springboards, too - Borbély leaves with a consideration of neurochemical factors, as well as a little chart suggesting that the process may be use-dependent rather than simply a factor of time. But I'll probably get to that another day. For now, enjoy Borbély's two stage model!

This is your brain on sleep... fakin' it.

So I've talked a little bit about sleep and memory formation prior, and it's actually a fun topic for me. So I'm running with it.

Now, there's a lot more in the field of normal memory, and I'll get to that eventually, but there's always a fun side-field to memory research - FALSE memories. In other words, you just KNOW it happened... except it didn't. You made it up. Except you didn't really make it up intentionally, but for whatever reason, it didn't happen but you think it did. And then your head hurts.

This is false memory, for the most part. It's a big field, and a lot of theories behind it, like the idea that we tend to remember generalizations more than we care to admit, and a lot of the detail-filling-in is reconstruction. This at least the generally accepted form, in brief, as to what happens (although I can't say I experience this a lot, because I just forget everything anyway).

Anyway, the most common paradigm in false memory research is the Deese-Roediger-McDermott paradigm (DRM) - basically, throw a bunch of words at someone with a 'theme' and people will be SO SO SURE that you said the word that fits the theme. For example, in the paper the authors use the wordlist door, glass, pane, shade, ledge, sill, house, open, curtain and then with that, there is a pretty high chance that the participant will report having heard the word window... even though you said no such thing. (In the DRM, these words are the 'critical words'.) The original research with the list showed that a 2-day delay produced HIGHER levels of false recall than true recall.

Payne, J., Schacter, D., Propper, R., Huang, L., Wamsley, E., Tucker, M., Walker, M., & Stickgold, R. (2009). The role of sleep in false memory formation Neurobiology of Learning and Memory, 92 (3), 327-334 DOI: 10.1016/j.nlm.2009.03.007



So, subjects here: 101 WEIRD Merrimack college sophomores, repeated with 84 WEIRD Harvard college sophomores. (Actually, we don't know that they're sophomores... that's me making up information.) Give them eight DRM wordlists. Two long-term groups - study at 9 AM and repeat at 9 PM, and study at 9 PM and repeat at 9 AM - and two short-term groups - study at either 9 AM or 9 PM and repeat 20 minutes later. The latter was a baseline, mainly to see if there were circadian effects (this is HARD to control for well, though, in sleep/memory research, and I don't think anyone has ever done it very effectively because it's practically confounded by nature).

Anyway, what did they get?

The sleep group had better recall. No big surprise - they remembered about six more words on average (out of the 96 total - 8 groups of 12 words each). Both groups had similar intrusions (non-critical words 'remembered'), but the sleep group showed on average one more critical word recalled. Because of the similarity in intrusions, but difference in critical words, the authors suggest that the false critical words aren't simply a by-product of having more overall recalls.

There's two more parts to the experiment, trying ever so more to zoom in on what's going on. A second experiment found a negative correlation with the amount of slow wave sleep and recall rates, but no significant difference in the number of critical words recalled - this experiment was smaller, and thus greater variance, and there's only eight critical words after all. Part 3 was a nap study, and the authors see (significant) greater critical word recall in the sleep groups compared against the no-sleepers, without a significant effect in the true-recalls or intrusions.

Question on part 3 - The authors conclude that slow wave sleep preferentially favors critical recall over true recall. But on what basis? Well, that critical recall between sleep/no-sleep was above significance threshold, tested against the null, but not for true recall. But wouldn't you want to be comparing the differences against each other, and then look for significance? Granted, looking at the graphs, it should pass that test - the recall measures look almost identical for the sleep/no-sleep peeps, but really... methinks you did the wrong test. I enjoy the enthusiasm in running multiple experiments, and I think their data probably do support their tentative conclusion from 3... but they didn't test it right, unless I happened to misread it.

So the authors suggest that a big part of the DRM's success in getting false critical words is that in the delay, there is sleep. Fair enough. And it's actually a good paper to show that sleep and memory work is hard, and results can be confusing and seem to run counter to each other sometimes (although this is often an effect of the constructions we use to 'divide' types of memory.

Medical students + Sleep deprivation = Plagiarism?

Say it ain't so!

Dr. Free-Ride notes the diminished moral capacity of students applying for medical residencies.

Days later, Allison pulls out a study showing worsened moral reasoning of sleep deprived military officers.

Coincidence? I think not!

Kuhn's Structure Part One: Normal Science

I suppose the title may be a white lie - I actually want to talk about Thomas Kuhn's approach first, and then I can get on to his account of normal science. See, prior to The Structure of Scientific Revolutions (hereafter referred to as Structure), Logical Empiricism held sway for most discussions of the philosophy of science. They're a very interesting bunch, and in fact I'll no doubt cover them someday, although I'd like to get my hands on some primary literature by A. J. Ayers and Carl Hempel before I try to discuss it much. Basically, the Logical Empiricists (also known as Logical Positivists, although they didn't like the association with Auguste Compte from being called Positivists) were very concerned with working out the normative description of science, and in giving it a special epistemic status wanted to work out the logic governing "good" scientific practice.

Kuhn would have none of it. Well, maybe that's overstating, but he didn't see eye to eye with them. His original training was in physics, but he was instructed to teach a course of the history of science for non-science students, and the rest, as they say, is history. As opposed to a logic of science, or any progressive pattern, he saw a number of seemingly rational yet incompatible theories arising in conjunction. If there was to be something epistemically special about science, it had to be expressed in science as practiced, not science as constrained and never practiced.

So he bases his story of science and its special status by examining its history, and here we have a rather novel (for its time) approach. There are two big parts to Structure - normal science, and revolutionary science.

Here, I'm primarily concerning myself with normal science. This is partly because it's treated by Kuhn first, and partly because understanding revolutionary science doesn't make much sense without understanding normal science first. I'll get to revolutionary science later, and then go back and analyze it a little more in depth after that. However, before any critical treatment of the arguments, I like to take the writing for granted until it's been digested.

So we have normal science - in Kuhn's description, this is "researched firmly based upon one or more past scientific achievements, achievements that some particular scientific community acknowledges for a time as supplying the foundation for its further practice." These achievements are "sufficiently unprecedented to attract an enduring group of adherents away from competing modes of scientific activity" and "sufficiently open-ended to leave all sorts of problems for the redefined group of practitioners to resolve." (If I quote Kuhn heavily, it's because he's actually very readable.) Achievements of this sort result in a research program as governed by a paradigm. (If you've heard that word used in common usage often, blame Kuhn.)

A paradigm for Kuhn is basically the school of thought, complete with theories, heuristics, and instrumentation, that arise from a successful and sufficiently convincing achievement. The whole idea will go together a little better, regarding how paradigms arise, once we get to revolutionary science. For the mean time, suffice for a rougher understanding of a paradigm.

A paradigm establishes itself and researchers run with it. You have your overarching paradigm, which includes a set of theories, like the Newtonian laws of motion in the Principia, as well as your examples of problem solving within the paradigm. New students to the science learn about relevant examples in the paradigm by training, and are generally indoctrinated into it, being given examples of application. These are generally not explicit, else there would be little use for the hammering out of details that governs normal science - in fact, this non-explicit statement leads Kuhn to pull out the Wittgensteinian "game" analogy, noting that learning is by iteration of similar things with the goal of getting a feeling for the methods acceptable to the paradigm.

So within the paradigm, the benefit of normal science is puzzle solving ability. Kuhn describes this as puzzle solving because researchers tackle problems for which there is presumed a solution. This solution is generally expected by the theory but not confirmed. He notes explicitly that paradigm governed research is, in fact, a lot of "mopping up" of the details, tedious work that is generally not acknowledged by non-scientists. Paradigms don't aim for "unexpected novelty." (A break with Popper, certainly, who held that disconfirmation and novelty was the business of science. We'll get back to him in revolutionary science, though.) Sometimes anomalies are found, especially in paradigms that encompass a sufficiently large aspect of natural inquiry, and in these cases either the theories are tweaked or refined. However, it is generally not accepted within most paradigms to just 'add in' and explicit statement of '[Y holds] except in instance of [anomaly X]'.

Part of the puzzle solving ability also lies within the apparatus used by scientists. Kuhn makes a strong point of early research in electricity attempting inquiry by use of a pan balance, and found no consistent regularity - it was not until Coulomb that special apparatus was created for measuring point charges, and these became objects of inquiry once the means of measuring them was available. If there are questions which are not accessible by the instruments accepted by the paradigm, then the research program encompassed by the paradigm generally ignores them.

While paradigms usually don't do much in the way of novel discovery, Kuhn does seem to have a role for discovery and invention (terms he uses almost interchangeably, since there seems to be little difference for him in stating that one discovers facts or that one manufactures facts - for reasons to be evident later). He notes in particular the discovery of X-rays. Although the paradigm of prior established electromagnetic radiation explicitly allowed for X-rays, practitioners were dismayed to find that cathode ray tubes were emitting more than they thought they were - and so research had to be re-done to establish that it was not confounded. This, for Kuhn, still falls in the heading of normal science, since the paradigm wasn't replaced with anything new, but simply tweaked to make room for a new phenomena that fit beside what was already established. In this means, Kuhn argues, there can be novel discovery without a paradigm shift.

*gasp*

Okay, we've covered half of Kuhn now. I know that's kind of long, but HALFWAY THERE. And we're past the boring part. Revolutionary science is where all the excitement is!

Slow posting, or what may be coming up

So I'm (not so) secretly a big fan of philosophy of science - I think many neurogeeks are - and I'm currently trudging through Kuhn's Structure. There should be a post soon about it; it's not that long, but I'm trying to go through it carefully.