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the best kind of sleep

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Canto: So Dr Seheult tells us that the most important sleep is in the earliest period. This is called slow-wave sleep or N3 sleep. It doesn’t last long, maybe half an hour…

Jacinta: Why is it called N3 sleep?

Canto: Well, here’s the detail – you have three stages of this early sleep. N1 is when you fall asleep. It lasts no more than ten minutes generally until you’re really there, in sleep. Then there’s N2 of course, which lasts from 30-60 minutes, your muscles relax and you begin to enter this slow-wave, also called delta-wave or delta brain activity sleep. That’s the deepest sleep of the night, at its deepest in the N3 period.

Jacinta: Well that explains the 1-2-3, sort of, but what about the N?

Canto: I haven’t been able to find that out specifically, but these are all phases of NREM (non-rapid eye movement) sleep, which are followed by the REM phase. So I think the N is just short for NREM. Anyway there are two types of sleep for maintaining good health – slow wave sleep and REM sleep towards the end of the night…

Jacinta: But don’t those two make up the whole of the sleep cycle?

Canto: Let me tell the story. Slow wave sleep is when you secrete valuable growth hormone, vital for children, in the time before midnight, according to the good doctor.

Jacinta: But I virtually never sleep before midnight.

Canto: Well you’re not alone there. In cities now, which are growing ever larger, we’re going to bed later and getting up earlier, and so sleeping less…

Jacinta: But generally living longer. So what’s the problem? I’ve heard that Hong Kong, which is about as urban as it gets, has the longest life expectancy on Earth – but that was probably measured before the China crackdown haha.

Canto: Well it’s no joke that China’s thugocracy will jeopardise everything in HK’s future, but good public healthcare and a very low infant mortality rate helps. People today can still live well with diabetes, obesity and slow-developing cancers, but they’d be even better with good sleep habits, if the rat-race allows them. But cities present us with a kind of eternal daylight, at great cost, not only in electric lighting, but in lack of sleep. Not to mention brightly lit screens that we take to bed with us…

Jacinta: Okay so what are the other benefits of slow wave and REM sleep, however delayed?

Canto: Dr Seheult describes a study showing that general sleep deprivation actually reduces the levels of antibodies produced after influenza vaccination. That’s to say, vaccination is less effective for the sleep-deprived. Another study used rhinovirus, a common cold virus. They paid students to be infected and found that those with good sleep efficiency, that’s to say, a high ratio of in-bed time to sleep time – their risk of being infected was reduced five to seven-fold, an extraordinary result. Actually this ‘extraordinary result’ finding comes up again and again in Matthew Walker’s book.

Jacinta: Yes, but it’s surely good to be awake sometimes too. But again, what is it about slow-wave and REM sleep that provides such benefits. What are the mechanisms?

Canto: Well, we’re talking about N3 sleep, the deepest sleep. This sleep phase is particularly important for memory consolidation, the stabilisation of a memory trace once it’s been acquired – meaning presumably the event itself, or its impact. It’s also called sleep-dependent memory processing. Now, how this precisely works is still being researched, but it appears to have much to do with interactions between neurons or neuronal complexes in the neocortex and the hippocampus. So here I should introduce sleep spindles, which are essential to all mammalian species.

Jacinta: They’re brainwaves, aren’t they?

Canto: Neural oscillations, indeed. They’re generated in the thalamic reticular nucleus (TRN), in richest quantities during N2 and N3 sleep. Wikipedia tells me this:

The density of spindles has been shown to increase after extensive learning of declarative memory tasks and the degree of increase in stage 2 spindle activity correlates with memory performance.

This is confirmed in experiments described in Why we sleep, showing that people who slept for a night between being asked to memorise certain data, like putting a name to a face, did a significantly better job than those who tried to remember the data after eight hours without sleep (from morning to evening). During the sleep period, subjects’ brain waves were recorded, and this is Dr Walker’s account:

The memory refreshment was related to lighter, stage 2 NREM sleep, and specifically the short, powerful bursts of electrical activity called sleep spindles… The more sleep spindles an individual obtained during the nap, the greater the restoration of their learning when they woke up. Importantly, sleep spindles did not predict someone’s innate learning aptitude. That would be a less interesting result, as it would imply that inherent learning ability and spindles simply go hand in hand. Instead, it was specifically the change in learning from before relative to after sleep, which is to say the replenishment of learning ability, that spindles predicted.

Jacinta: So they were correlating the number of spindles with their memorising performance, and memory here is being equated with learning. Is that right? I mean, is learning really just memorising?

Canto: Well, no, but it helps. I’m trying to memorise Newton’s inverse square law for gravity, but I know that even if I can reel it off like a favourite poem that doesn’t mean I fully understand it. Let me see G = m1.m2 over r². I’m not sure if that’s right.

Jacinta: Yeah, basically you have to know that the gravitational attraction between two bodies is equal to the product of their masses divided by the square of the distance between their ‘centres of mass’. I think. Though why that happens to be the case I have no idea. Does anyone?

Canto: Because… the universe? I’m beginning to feel sleepy…

References

M. Walker, Why we sleep, 2017

https://www.uofmhealth.org/health-library/hw48331

How to get the best sleep for your immune system | Roger Seheult (video)

https://www.oal.cuhk.edu.hk/cuhkenews_202101_life_expectancy/

https://www.ncbi.nlm.nih.gov/books/NBK526132/

https://en.wikipedia.org/wiki/Sleep_spindle

Written by stewart henderson

November 14, 2021 at 12:54 am

Posted in memory, mind, science, sleep

Tagged with , , ,

a post to send you to sleep, or not

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Häggström, Mikael (2014). “Medical gallery of Mikael Häggström

 

Canto: Anything interesting you’ve learned lately?

Jacinta: Well, there’s so much, it’s hard to keep track of it all, before it slides down the slippery slope into a past of fragmented memories.

Canto: A pasta of memories? That’s food for thought. I know you’ve been reading up on sleep, among all your other heavy reading. Tell me.

Jacinta: Yes, I’ve been reading up on feminism and misogyny as you know, which is mostly depressing, but this sciencey but very accessible book, Why we sleep by Matthew Walker, is not so much depressing as worrisome, for those of us whose sleep patterns are all over the place, like mine. He’s a big-time sleep researcher, and what he says about sleep deprivation is all bad – even for a wee bit of it.

Canto: So, those dreams of doing away with sleep, of zapping your brain for a few seconds to provide the instant reinvigoration that sleep takes eight hours of wasteful oblivion to achieve, allowing us that much more time to ruin the biosphere and all, or just to read more books and shit, those dreams are just a waste of sleep?

Jacinta: No zapping will ever replace the complexity of sleep, with all its REMness and non-REMness, let Mr Walker assure you. Sleep is a restorative and builder, which has complexly evolved with the complex evolution of our brains and bodies. And by ‘our’ I don’t just mean humans, but every complex or not-so complex evolved organism. They all sleep.

Canto: Well, there are many questions here. You’ve mentioned REM sleep, which I think has something to do with dreaming – your eyes, presumably under their lids, are rapidly moving about. Why? It doesn’t sound healthy.

Jacinta: They’re responding to brain signals, and it’s perfectly normal. More specifically, they seem to be responding to the brain’s changing visual representations while dreaming. They used electrodes in the brain to discover this – which sounds Frankensteinish but in this case they were patients with epilepsy preparing to have very invasive treatment to stop their seizures. They looked at activity in the medial temporal lobe, a region deep in the brain which includes the hippocampus and amygdala, and is involved in encoding and consolidating memories, and found fairly clear-cut connections between that activity and patients’ eye movements.

Canto: But how could they ‘see’ the eye movements?

Jacinta: Oh god, I don’t know, for now I’m more interested in sleep deprivation, which raises concerns for everything from diabetes to Alzheimer’s. And, although I haven’t measured anything carefully, my guess is that I average 6 to 7 hours’ sleep a night, and I need to amp that up.

Canto: And you’ve recently been diagnosed as pre-diabetic, so do you think more sleep can help with that? It’s usually pretty strongly correlated with diet isn’t it?

Jacinta: Less time sleeping, more time for eating, Walker writes. I’m certainly trying to lose weight, but only by eating less. I think my diet’s not too bad, less wine though. And I suppose if I slept more, which is easier said than done, I wouldn’t eat so much. I’ve found in the past that just reducing the quantity of food I ingest, without changing its make-up – in other words, being more disciplined – can take the weight off quite quickly. The key is to make it life-long.

Canto: More fibre is good, I think. For the microbiome.

Jacinta: So type 2 diabetes is generally about blood sugar levels and their regulation, or lack thereof. In a healthy person, eating a meal adds glucose to the blood, which triggers the hormone insulin, produced in the pancreas, to somehow bring about cellular absorption of the glucose as an energy source. In the case of diabetes, there’s usually a break-down in the cellular response to the insulin signal, I think, and so you become hyperglycaemic – not that this has ever happened to me, so far.

Canto: So how does this relate to lack of sleep, apart from giving you more time to guzzle sugar?

Jacinta: Walker describes a series of studies, independent from each other, in different continents, which found high rates of type 2 diabetes in people who reported sleeping for less than six hours a night on a regular basis. They controlled for other factors such as obesity, alcohol use, smoking etcetera. But of course correlation isn’t causation so they investigated further. They conducted experiments with a bunch of healthy people – no blood glucose problems or signs of diabetes. Firstly, they mildly tortured them – they permitted them only four hours of sleep per night over six straight nights. Then they tested their ability to absorb glucose, and found a 40% reduction in that ability. This would immediately classify them as pre-diabetic, and these studies, I’m assured, have been replicated numerous times.

Canto: That sounds incredible. And these guinea pigs quickly recovered? Or are they now full-blown diabetics? Doesn’t sound like mild torture to me. And do they know why a week’s sleep deprivation had such a dramatic effect?

Jacinta: Ha, well, Walker doesn’t mention the afterlife of the experimental subjects, but I’m assuming normality came bounding back after they recovered their sleep. As to the mechanism of action, Walker describes two options – sleep loss may have blocked the release of insulin by the pancreas, providing no signal for cell absorption to take place, or it may have interfered with the released insulin’s message to the cells. And though it seems that sleep loss probably had an effect on both, it was clear from biopsies taken from subjects that it was the latter, the cells’ lack of response to insulin, their ‘refusal’ to take up the blood glucose, that was the principal problem.

Canto: Just looking at the Sleep Foundation website, and they seem to get things the other way round, that diabetics are suffering from sleep loss. I must say, that, off the top of my head, I’d find being pre-diabetic easier to manage than my sleep behaviour. I mean, I can imagine changing my diet and exercise habits easily enough, but my sleep habits not so much. How do you turn off your brain?

Jacinta: Well, Mr Walker has some suggestions on that, which we’ll explore next time. And by the way, there seems to be tons of videos and websites providing knowledge and advice on the issue, which always makes me feel superfluous to requirements as a human being…

Canto: Well, try not to lose sleep over it.

References

Why we sleep, by Matthew Walker, 2017

https://www.sciencealert.com/scientists-have-worked-out-why-your-eyes-move-when-you-re-dreaming

https://en.wikipedia.org/wiki/Sleep_deprivation

https://www.sleepfoundation.org/physical-health/lack-of-sleep-and-diabetes

 

Written by stewart henderson

November 7, 2021 at 3:56 pm