Ever have trouble remembering where you just left your keys? Just laugh it off. New research suggests that humor can improve short-term memory in older adults. In a recent small study conducted at Loma Linda University in Southern California, 20 normal, healthy, older adults watched a funny video distraction-free for 20 minutes, while a control group sat calmly with no video. Afterwards, they performed memory tests and had saliva samples analyzed for stress hormones. You guessed it; those who got to laugh the 20 minutes away with the funny video scored better on short-term memory tests, researchers said. And salivary levels of the stress hormone cortisol -- a memory enemy of sorts -- were significantly decreased in the humor group. The less stress you have, researchers said, the better your memory. It works like this: humor reduces stress hormones, lowers your blood pressure, and increases your mood state, according to Dr. Lee Berk, a co-author of the study. The act of laughter -- or simply enjoying some humor -- increases endorphins, sending dopamine to the brain to provide a sense of pleasure and reward, Berk said. That, in turn, makes the immune system work better and changes brain wave activity towards what's called a gamma frequency," amping up memory and recall.