Study: Humans Yawn to Cool Their Brains

Researchers suggest yawning may have a radiator-like function.

Researchers at Princeton University believe they’ve finally uncovered the mystery behind why humans yawn: yawning cools the brain. According to their theory, yawning causes a stretch in the jaw which increases blood flow in the head area. Then, breathing in forces spinal fluid and blood from the brain to move downwards, cooled by air from the mouth. To test out their theory, they studied rats, parakeets and humans to see if they yawned more in cold air. While the evidence that people yawn more in cold conditions seems solid, other scientists suggest the real reason for yawning may be more social than physiological, serving as a social cue to indicate sleepiness or boredom. Take note, Al Gore.