Oh, excuse me. I just had to yawn. You know, those stretch out your arms, throw your head back kind of yawns. Now, where was I? Oh, yes. I was just reading a scientific article on yawns. My yawning aside, it was very interesting, dispelling everything I thought I knew about yawns.

Yawns, what do you know? T or F?

1. They are contagious.

2. They regulate heart rate.

3. Unborn babies yawn.

Yawns last between 4 and 7 seconds. We flop open our mouth, take a deep breath and then forcefully exhale. Why do we do it? We humans are not the only primates that yawn. Gorillas, tigers and dogs yawn. Non-human primates including birds, fish and turtles also yawn. The question as to why we yawn has vexed scientists for centuries. Historically the most common theory has been that we yawn to regulate oxygen and carbon dioxide levels in our blood. This has been disproved. New thinking, supported by recent research, suggests that we yawn to lower the temperature of our brains. This is called brain thermoregulation and it appears to be the primary reason we spontaneously yawn. Hot brain. Cool air. Big yawn. Cooler brain.

There are two forms of yawning, spontaneous and contagious. It appears we spontaneously yawn to cool our brains and we contagiously yawn because we imitate our social environment. So, if you have a warm brain and yawn, your friends and office mates will likely join in on this peculiar social custom. Even the mere suggestion of a yawn, like when I was reading the research paper, can elicit a yawn.

Brain thermoregulation appears to be the single most important reason for yawning. Higher brain temperature corresponds to decreased arousal, so a spontaneous yawn will perk you up. In a group, contagious yawning serves to collectively arouse. Having a group with the same level of alertness may help complete tasks or, in a more dangerous, primitive time, ward off invaders.

Yawning is most common in summer when temperatures are higher, causing increased body and brain temperature. The air, which is cooler than the body and brain, enters the mouth and nose and, through neural and direct mechanisms, lowers brain temperature. As ambient air temperature nears or exceeds body temperature, yawning is less frequent because the air is not likely to cool. Your body certainly would not want to take a big gulp of warm air and heat up your brain even more. Likewise, in cooler weather, when body and brain temperature is normal or slightly cooler than normal, there is less need for yawning.

All humans do it. Even unborn humans do it. Finally, we may be getting to a point where research is providing good evidence to explain just why. Centuries ago Hippocrates thought that yawning served to release fever. Now in 2014 we are coming back to the thoughts of arguably the greatest physician scientist in history. With only his supreme powers of observation and without the benefit of technology such as electronic air temperature gauges, hygrometers and continuous internal body thermometers, Hippocrates got it right. The body yawns to decrease temperature. He may have had the fever part wrong but his basic idea was spot on. Centuries ago.

I am yawning now. Would you like to join in?

Answers: 1. T; 2. F ; 3. T.

Dr. Lori Boyajian-O’Neill can be contacted at lori.boyajian-oneill@hcahealthcare.com.