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Stanford Report, December 10, 2003

Laughter, like drugs, tickles brain’s reward center What happens in your brain when you find something funny?


Love might be a drug, but humor and laughter have much more scientifically plausible — and some might say pleasurable — rewarding qualities, say researchers at the School of Medicine and Lucile Packard Children’s Hospital.

Using comic strips with and without the punch lines, the investigators traced the pleasurable aftermath of "funniness" to a region of the brain involved in the response to methamphetamines and cocaine, as well as monetary gains and the site of attractive faces.

In their study, researchers monitored brain activity in a group of volunteers while showing them a series of cartoons. Some of the cartoons had key elements removed to diminish their funniness. Illustration:Courtesy of Allan Reiss

"This is the first time that the reward system of the brain has been linked to humor," said Allan Reiss, MD. "The finding is potentially significant in terms of understanding normal variation in personality and behavior as well as certain brain disorders such as depression." The research was published in the Dec. 4 issue of Neuron. Reiss is the director of the Stanford Psychiatry Neuroimaging Laboratory and co-director of the Center for Brain and Behavior at Packard Children’s Hospital.

Although previous research had identified the regions of the brain involved in understanding the language and meaning of a joke, and those required to move the muscles necessary to smile or chortle in appreciation, no one knew until now why humor feels so good to most people. This understanding could lead to new diagnostic tests and therapies for a variety of psychiatric disorders.

"You don’t need an imaging study to show that some people use humor as a very effective coping or stress-reduction mechanism while others do not," said Reiss, who is also professor of psychiatry at the School of Medicine and chief of child and adolescent psychiatry at Packard Children’s Hospital. "It’s possible that people who rely less on humor simply find it less rewarding. We’re trying to understand this personal variation and how it relates to basic behavior and brain function."

In the study, 16 young adults were plied with 84 black-and- white cartoons. As the participants viewed each cartoon, the researchers simultaneously monitored blood flow in several regions of their brains using a technique called functional magnetic resonance imaging. After the imaging session, the subjects rated the "funny factor" of the cartoons they had viewed in the machine.

The researchers polled family, friends and students to develop a portfolio of cartoons to minimize gender or cultural biases that may have affected the results. They then created an unfunny version of half of the cartoons to use as controls by removing essential visual or written cues.

"The pre-screening of the cartoons were some of the funniest lab meetings we’ve had," said Reiss. "What’s brilliant about some of these cartoonists is how perfectly they juxtapose the line drawing with the caption or a subtle visual perspective. If you change either one, the cartoon becomes completely unfunny."

The researchers found that the giggle-inducing cartoons activated a network of regions of the brain, including an area called the nucleus accumbens, or the NAcc, and another called the amygdala. In the NAcc, which is known to be involved in the rewarding feelings that follow monetary gain or the use of some addictive drugs, the degree of activity correlated with how funny the subject thought the cartoon was; extremely funny clips resulted in more blood flow to the area than less funny competitors, confirming the NAcc’s role in humor appreciation.

The amygdala’s involvement is also telling. Dysfunction in this region of the brain has been implicated in some pathological disorders, as well as in depression, and other diseases including Parkinson’s and fragile-X syndrome, a disorder often marked by symptoms similar to attention deficit disorder and autism.

The involvement of a reward center that responds to addictive drugs elicits an obvious question: Can humor itself be addictive? In other words, can inappropriate fits of irrepressible giggles be blamed on a brain-signaling blip rather than a heartless disregard of societal expectations? While the idea of biological absolution is tempting, Reiss isn’t convinced.

"Although it may be involved in addiction, the brain’s reward center has evolved to enhance learning and behavior through positive feedback," said Reiss. "It’s meant to allow people to learn from and perform in their environment in as optimal a way as possible."

More important than identifying the existence of hypothetical humor junkies, the scientists’ finding may one day allow better diagnostic testing for a variety of conditions.

"One of the key symptoms of depression is lack of a sense of reward from previously rewarding activities," said Reiss. "Assessing how the brain’s reward center responds to humor may turn out to be the simplest and most direct way to identify people suffering from mood disorders. I think the applications of this work range from a better understanding of basic behavior and social interactions all the way to important clinical issues."

Lucas Center celebrates first decade of imaging research (5/29/02)

Happy faces trigger different brain reactions in extroverts and introverts (6/21/02)