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Comment by ndh2 | Hacker News Reader

What is the connection between swimming and heat? How did they even arrive at this hypothesis? Why would rats need to catch up on heating their brains, days after missing REM sleep?

The facts are interesting, the conclusion doesn't make any sense at all to me.

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It doesn't make any sense at all to me either. Because of the difference in specific heat and heat conductivity of water vs air, an animal that can sleep under-water (even whilst alternating the sleeping part of their brain), surly doesn't need to warm its brain while on sleeping on land.

(But I'm no expert.)

It could be that the cooling of the brain is dominated by convection through blood flow rather than conduction through the skull/fat/skin. If that's true, then the effect of water vs air would be on the whole body which still has to be maintained at proper body temperature so there would be no difference in brain temperature sleeping the same way in water or in air. If the body's temperature regulation is designed assuming that the brain is always generating too much of its own heat and doesn't need to be supplied with additional heat like the extremities do, then, it would still need to keep up that heat generation independently of the rate of heat loss to the environment.

It's weird to me too. But articles says it's because the brain alternates activity in hemispheres. It switches activity to each hemisphere, possibly as it gets too cool.

>These marine mammals have evolved a half-brain style of sleeping, perhaps as a way to remain alert enough to avoid predators and drowning.

>Because part of the brain is always active, it’s always warm. As a result, it never triggers R.E.M. sleep.

It's weird they don't mention the much more obvious fact that an air-breathing mammal might need to maintain some level of alertness when sleeping in water.

From the article: "These marine mammals have evolved a half-brain style of sleeping, perhaps as a way to remain alert enough to avoid predators and drowning."

Regarding the rats: the study has an explanation for that too. It says the rats were woken up thousands of times a day, and they are catching up on the lack of sleep rather than lack of REM.

The article says they have more REM after they miss out on it. The ratio is not the same as normal sleep.

Doesn’t make any sense to me. I don’t really think that people sleeping in warm countries have less R.E.M. sleep than people sleeping in cold countries...

The issue with your statement though is that people in colder climates adapt via technology to keep a comfortable environment at night (houses, blankets, etc). So it’s not the kind of comparison that you can make like that.

If anything, it could be the reverse, it's just too complicated to immediately see. As another counter-obviousness example, living in a cold environment helps you lose weight because your body has to generate more heat all the time. But in real life, people keep their bodies warm with clothes and houses and actually gain weight in winter because they eat more and don't go outside and exercise as much. Just because the weather's cold or hot, doesn't mean people are.

Sounds like pseudo science to me.

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