So, can you get brain freeze from breathing in exceptionally cold air? Say, below -20 F? I swear this happened to me once last winter.

i always believed it was the cold hitting the stomach, which sent signals to your brain stating that the stomach may be in pain, caused by the coldness

I have my own remedy for brain freeze - based on the “blood vessel phenomenon”, except what I was told that it’s your carotid (neck) arteries that are the dilating culprits so I warm my neck with my palms when it happens. Seems to work.

You can also put your tongue on the roof of your mouth. That seems to help fix it for me.

From Wikipedia:

“A brain freeze is caused when something very cold, like ice cream, touches the top palate in your mouth. The blood vessels constrict due to the cold. As the palate warms, the blood vessels suddenly enlarge and the blood rushes back to the blood vessels. The nerves in this area send a signal for pain to the front of the brain, resulting in a brief but intense headache.”

To clarify - the carotid artery theory is based on the idea that ,as those arteries contract from cooling, the blood pressure in your brain increases and that’s what causes the pain, not some strange nerve signal from your palate. As a surfer i have also experienced an “ice cream headache (brain freeze, same thing)” merely from having my head submerged in cold water while holding my breath with a closed mouth. This would seem to discount the theory that the cooling of the palate is what causes the headache.

Study of anatomy will prove that the carotid artery therory doesnt hold water, the artery inst close enough to the throat, really it isnt, I know it looks like it is but its not, to cool the blood down significatly enough to also cool the brain. The artery is warm, the blood is warm, the throat is warm, the esophagus is warm, so how can something get the esophagus so cold that the throat gets so cold that the artery gets soo cold, that the blood gets soooo cold that the brain freezes? Its a stretch.
It also cant be the cold food in the stomach for the same reason, our b ody warms food up (or cools it down) before it gets to the stomach.
Try an experiment, put an ice pack on the side of your throat, do you get a brain freeze? Now hold an ice cube on the roof of your mouth, do you get a brain freeze?
You be the judge
As forthe head being sumerged in cold water, again look at the anatomy involved, we have loads of nerves just under the scalp on our heads, and loads of blood vessals, that is why a head injury, even a small one, bleeds so much. Your head being in the cold water so long encourages those lood vessels to contract, causing the pain. Not your artery, if your blood (from the artery) to your brain got that cold, you would have a bigger problem thana headache.

I have it referred to as spheno palatine ganglia neuralgia. At least I think that was how it was spelt.

is it the same as when you dive into a pool on a winter evening and some water enters your nostrils and cause a headache?

‘Bout the carotid artery theory, the theory does not fit with PGN.