In one of his numerous studies on laughter, Richard Davidson, professor of psychology and psychiatry at the University of Wisconsin in Madison, hooked subjects up to EEG (electroencephalograph) machines, which measure brain wave activity, and showed them funny movies. Smiling made their happy zones click wildly. He proved that intentionally producing smiles and laughter moves brain activity towards spontaneous happiness.
Arnie Cann, professor of psychology at the University of North Carolina, discovered that humor has a positive impact in counteracting stress. Cann led an experiment with people who were showing early signs of depression. Two groups watched videos over a three-week period. The group that watched comedy videos showed more improvement in their symptoms than did a control group that watched non-humorous videos. He also found that people with ulcers frown more than people without ulcers.
If you catch yourself frowning’ practice putting your hand on your forehead when you talk, to train yourself out of it.
Source: “Why You Should Take Laughter Seriously,” from The Definite Book of Body Language, by Allan & Barbara Pease