Overstimulated nerves

Brain freeze occurs because the temperature in the mouth and throat drops very rapidly. This rapid cooling stimulates the nerve endings and muscles around the small blood vessels in your oral cavity, palate, and sinuses. The blood vessels in your palate reflexively narrow to prevent excessive heat loss (vasoconstriction). Shortly after, they widen again to rewarm the oral cavity (vasodilation) (Chebini 2019).

The nerve endings around these blood vessels are extensions of a larger nerve, the trigeminal nerve, which runs from your cheek toward your temples and into your brain. This nerve is essential for sensory perception in your face and the control of your chewing muscles, but also for the sensation of pain.

Constriction and dilation of blood vessels

You might think that the constriction of blood vessels in the oral cavity causes the pain (like a kind of cramp). However, new research shows that it is actually the dilation that is experienced as pain. This is because the trigeminal nerve also has a direct connection to larger blood vessels in the brain. These are the anterior and middle cerebral arteries (arteria cerebri anterior and media), which supply the front and middle sections of the brain with blood respectively. The trigeminal nerve also connects to the meninges, which contain numerous small blood vessels. The brain itself has no pain receptors, but the meninges do.

The constriction of blood vessels in the oral cavity and the cold itself stimulate nearby receptors of the trigeminal nerve, causing them to send signals to the brain. This leads to a dilation of the large cerebral arteries, which temporarily increases blood flow to the brain. This dilation of the aforementioned arteries is then experienced by us as pain. So the trigeminal nerve can actually do both: it can detect changes in blood flow to the brain, but also cause changes in those same blood vessels. The pain is therefore not a direct result of cold, but an indirect result of how these signals are processed at the brain level. Researchers are still debating exactly which dilation of which blood vessel is responsible for the pain (Blatt 2012, Terrier 2021, 2022, Hensel 2019).

A protective reflex

Once blood flow to the brain returns to normal levels, the pain of the brain freeze also subsides. The prevailing theory at this point is that this is a kind of protective response by the body. The brain is highly sensitive to temperature fluctuations and functions best when temperature is kept constant. The brief increase in blood flow to the brain therefore prevents it from cooling down too quickly or too much. This vasodilation response is a true nerve reflex that is most likely also involved in migraine and cluster headaches (Khan 2019, May 1999).

What can you do about it?

Besides being only briefly unpleasant and entirely harmless, you can resolve a brain freeze by stopping the cooling in your mouth and shortening the duration of the reflex, simply by raising the temperature again.

• Press your tongue against the roof of your mouth to directly warm the small blood vessels in your palate.
• Drink something warm immediately after your ice cream or cold soda.
• Cover your mouth and nose and breathe warm air from your hands into your mouth and nose to rewarm the oral cavity.
  
  So the next time you enjoy your ice cream a little too fast: press your tongue against the roof of your mouth and you can get right back to enjoying it.