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Comment by stubish | Hacker News Reader

I don't understand why I would need to cool my brain more when I'm tired. I'm not buying the theory that yawns are for cooling brains without more details.

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I'm not buying the brain-cooling theory because a couple of yawns won't lead to anywhere near enough evaporative cooling to chill the brain by a few degrees. Also, the brain has a very very good blood flow with the rest of the body, so you really have the cool the whole organism.

The only area of the body yawning could have any kind of immediate cooling effect is the soft palate in the rear upper portion of the mouth—the part responsible for brain freezes when eating ice cream. I don’t think ambient air passing over that palate would create a measurable change in brain temperature.

Yawning always seemed, to me, to go hand in hand with stretching. I believe the reason we yawn is one in the same with the reason we stretch. By yawning, we are effectively stretching one of the few internal organs under our direct control: the lungs. It stretches the muscles involved in breathing, releasing trapped lactic acid built up over a long day of automated breathing. It improves blood oxygen concentration, which improves wakefulness and attention, which is exactly what you need when you are fatigued. Deep breathing also reduces anxiety, which is why breathwork is heavily incorporated in meditation.

I think the contagious aspect could be an evolutionary behavior. Social mammals tend to work in groups, and “contagious” yawning was likely naturally selected for since all members of an exhausted group who yawn would be more awake and alert in the event of an attack or when hunting prey. These are physically strenuous (and tiring) activities that directly affect the survival of the organism.

It changes air flow by stretching the fold between mouth and sinus, maybe it is a pre-sleep sinus stretch.

I guess because your brain overheating is what's making you feel tired in the first place?

That seems pretty easy to falsify. I still get tired in cold environments, do you?

I actually have an easier time maintaining flow in cold environments. I keep my house pretty chill and warm the rest of my body with warm clothes. Summer in South Texas was miserable for me, so I moved father north and could not be happier with the change.

It's not that I don't still get tired, of course I do. More that I'm less affected by the ambient heat.

Doesnt adenosine improve bloodflow to the brain when we are tired? If that is true, increased bloodflow should increase the brain temperature as more blood circulates and exchanges heat

Sometimes there are aspects of the brain designed for one purpose that get used for a total different one. For example, neurons that detect smell will trigger when we are thinking about purely moral issues, possible because it helps to boost the emotional reaction.

The body do cool down when it sleeps, and many people do feel aided in falling asleep if they lower their body temperature a bit. Yawning might just be that, a small trick to get the body to do a short temporary jump towards a more sleepy state, and a social ques with a minor biological aspect to trigger similar state in a social group. It could also be the other way around, that being a social trigger with a minor biological aspect attached that happens to have a real use in other animals.

To go to sleep your body temp needs to drop a couple degrees.

https://www.sleep.org/does-your-body-temperature-change-whil...

Maybe yawning helps you get to the right temperature.

Could just act as a little nudge in the right direction.

I think sighing, rather than yawning, makes more sense with the brain cooling theory.

When we are distressed, we release cortisol, which is a pro-oxidizing free radical that raises body temperature and blood pressure. Signing involves a fast and prolonged exhalation of air. We tend to sigh when we are distressed, so it possibly serves as a way to cool ourselves down similar to an exhaust fan on a desktop chassis.

I read somewhere that when we fall asleep our body temperature is lowered a bit, maybe that’s what’s happening?

Probably because the brain is what takes the most energy for us

There's also the social aspect of yawning - seeing someone yawn triggers a yawn... Maybe brains like to maintain a similar temperature to nearby brains.

Or yawning is just a communication mechanism, formed in a time before using words became commonplace and maintained because it works.

It might also be a type of communication which goes against the typical 'pack' animal communication hierarchy. It might make sense for the pack to sleep when any of the pack is tired, rather than waiting for the alpha-dog to feel tired. 'contagious' yawning allows that.

Hell, for me seeing a video of someone yawning can make me yawn. Even reading these comments... I seriously yawned three times just thinking about people yawning.

It's quite possible that it is a social signal, I think. Something designed to facilitate a non-spoken syn-ack handshake between members in a social group. I see you, you see me, I see that you see me, end of transmit.

Just to clarify, the hypothesis in the post above was intended to be humorous.

For me, even reading the word "yawning" so many times triggers yawning.

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