Anatomy of a Laugh

In the video above, we look at why laughing at unfunny things could be a red flag for a condition called frontotemporal dementia.

In the meantime, let's acknowledge the full-body weirdness that is laughter, starting with the contortions of facial muscles to create the mask of mirth.

The brain hears or sees something funny and cues muscle function and emotion. Fifteen muscles get in on the act, crinkling the eyes and contorting the cheeks. But it's the zygomatic major muscle – responsible for turning that frown upside-down – that gets all the attention.

Meanwhile the body's brain stem gets the message that hilarity is ensuing and that lung function is going to need to deal with the dual tasks of laughing and breathing, especially with the epiglottis half closing, causing a sputtering of air and vowels to issue forth.

In the form of ha, ha; hee, hee; or ho, ho. Every 210 milliseconds. Seriously, there's a study on that. You may even suffer emotional incontinence, aka tears.

All that guffawing puts extra demand on your body, like your heart. Which is now pumping faster to replace the oxygen that your fire hose of a mouth hole is expelling. While the face and stomach muscles contort, the rest of your muscles weaken, taking a break while the energy hog of laughter siphons off the body's resources.

And then there's the sweet, sweet flow of hormones in the form of endorphins, which, in concert with muscle weakening, can cause euphoria. At the same time, the stress hormone, cortisol, takes a brief holiday.

All within a duration of 75 milliseconds.

Now, what instigates that 75-millisecond laughter is an entirely different matter. And in this video, we explore the connection between laughter, personality and disease.