Understanding a joke involves "three basic components," reports Florence Williams in a New York Times review of Ha! The Science of When We Laugh and Why by Scott Weems. (3/18/14). The three parts are "constructing (sorting through relevant knowledge, experience and expectations), reckoning (jettisoning our errors and mistaken expectations) and resolving (reaching a satisfying, often surprising conclusion). See how your brain quickly does all three when reading the Leno-worthy headline: ‘Doctor Testifies in Horse Suit’."
Your sense of humor, can "depend on your age, your gender, your IQ, your political inclinations, how extroverted you are and the health of your dopamine reward system." Extroverts tend to laugh and make more jokes,"yet in tests measuring the ability to write cartoon captions, people who were more neurotic, assertive, manipulative and dogmatic were actually funnier. As the old saw holds, many of the best comics really are miserable." Moreover, "the funniest people don’t live longer" and are more likely to smoke and be overweight.
Studies do show, however, that humor "improves our health" and even "makes us smarter." Laughing "literally loosens up our blood vessels, promoting healthy circulation." One study found that those "who watched funny movies after surgery requested 25 percent less pain medication." Another found that "watching an episode of ‘Friends’ reduced anxiety three times as effectively as just sitting and resting." Those watching videos of Robin Williams doing standup or "reading funny jokes" also did better on "word-association problems."