Popular Science

A physiologi­cal dive into how a laugh spreads through your body

- SARA CHODOSH / JOHN DEVOLLE BY ILLUSTRATI­ON BY 5/ Extra endorphins spark joy—and dull physical pain— while relaxed blood vessels [I] help us loosen up.

THE OLDEST KNOWN JOKE DATES BACK NEARLY 4,000 years, and it’s a fart gag. The fact that we’ve been crackin’ wise for so long suggests there’s something innate about the need to laugh. Heck—chimps, rats, and perhaps even dolphins do it. Neuroscien­tists and psychologi­sts aren’t sure about the exact evolutiona­ry reason for a chuckle, though its ability to pep us up and promote bonding provide pretty solid clues. Whatever its underlying purpose, here’s how a good ol’ guffaw manifests in your body.

1/ When the frontal cortex [A]—an area responsibl­e for decisionma­king—realizes something is funny, it starts a cascade of neurologic­al responses.

2/ One signal hits the motor cortex [B]— which spurs the physical components of a giggle, including diaphragm contractio­ns and head bobs—and then the periaquedu­ctal gray [C], a chunk of nuclei in the brain stem that controls vocalizati­on.

3/ Another command hits the amygdala [D], thalamus [E], and hypothalam­us [F] (parts of the emotion-regulating limbic system) to trigger the endorphin rush that makes laughing feel so very good.

4/ Pings from the hypothalam­us prompt the pituitary [G] and adrenal glands [H] to start a wave of calm, in which stress hormones like cortisol and epinephrin­e dip.

6/ Humor also tickles our immune response through revved-up antibody production and activity in cells called killer Ts and Bs [J]. Docs aren’t sure as to the root of this superpower.

7/ Shared tee-hees help develop a sense of belonging. The Duchenne display—a smile controlled by the zygomatic major muscle [K] in your cheeks in which lips curl and eyes narrow—subconscio­usly signals glee to others.

8/ Good-natured chuckles cascade more slowly and at lower frequencie­s than malicious ones. That distinct sound tips off others that it’s okay if they laugh along.

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