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The search for the elusive funny bone has ended; it's located in the brain...and it isn't a bone.

Humor sometimes relies on culture and social mores to generate a laugh, but the foundation for everything funny is the same for all people—it's grounded in an expanded network of brain areas, each working to process one aspect of this multifaceted cognitive experience we call a joke.

How does the brain get it? It all starts when visual signals from a cartoon or auditory signals from a pun hit the brain. But the heart of what's funny in a joke is the mismatch between what we expect to see and what we get, something researchers call incongruity. Once certain brain areas process and flag this mismatch, a flurry of happy emotions and boats of laughter ensue, according to research studies with decidedly un-funny language.

Tracing a joke in the brain

The field of studying humor in the brain is relatively new, says Dr. Anjan Chatterjee, a professor and neurologist at the University of Pennsylvania. But over the past two decades studies have used brain imaging technologies to peek into the brain at the moment of a joke.

To understand what parts of the brain areas are involved in processing humor, scientists have to break down the components of humor, mainly the cognitive elements and the emotional response.

The cognitive aspects of humor require the brain to recognize the incongruity employed to make the funny point. It's necessary to identify and comprehend two juxtaposed ideas to get a joke. The short storyline of a joke works to undo the simple assumptions we automatically make at the start.

For example: "I went to buy some camouflage trousers the other day but I couldn't find any."

The joke works if you first think of camouflage as just the color description, and only at the end think of the function of camouflage apparel, which is, to hide from view.

To process this juxtaposition, studies have found that people employ multiple brain regions from parts of the prefrontal cortex to areas in the temporal lobe, as well as the anterior cingulate cortex, which is known for its role in error detection. After reviewing the findings of these studies, neuroscientist Jessica Black of Boston College and her colleagues suggested these mechanisms point to a core processing area, which includes the temporo-parietal junction.

Once the incongruity of a joke is resolved, it leads to amusement, an emotional reaction that activates the reward centers of the brain. The release of dopamine to help the brain process emotions enhances the experience of pleasure and increases serotonin levels that elevate mood.

This amusement is tightly linked to resolving the incongruity of the joke. As the saying goes, if you explain a joke, it's no longer funny.

"Those surprise element, where you internally have to have an 'ah-hah' moment where it all comes together, is a critical feature to then having that pleasure response," Chatterjee says.

This vast network for humor processing is as susceptible to malfunction as the rest of the brain, and sometime brain problems can render a person immune to jokes. Damage to brain tissue can make it impossible to detect two incongruent ideas, taking all the fun out of a punch line. And mental health issues, such as depression, can dampen the amusement generated by resolving the joke.

Comedy-loving human societies

The subjectivity of humor - what's funny to one person or culture isn't funny and might even be offensive to another person or culture - is more difficult to address. "Things that are social that are consistently social have an effect on the brain," Chatterjee says. But without an historical record of data over time, identifying what has evolved into elements of humor isn't as easy as identifying more primitive traits such as "fight or flight."

But whatever the reasons are, humor has a prominent role in all societies. Among the theories trying to explain this is the "superiority theory," which suggests that humor is a non-threatening way to present dissenting views or negative feelings in an acceptable way as a means to preserve the social structure and reinforce the social bonds instead of threaten them.

Another theory, "Tension-relief," identifies humor as a stress reducer that provides psychological relief from tension for individuals, as well as the group. The feel-good benefits produced by the endocrine system coupled, with the relief of muscle tension, can shift focus away from stressful behaviors such as constant vigilance. And another theory holds that humor plays a role in sexual selection as an indicator of a qualified mate.

As theories go, these make sense to Chatterjee.

"People feel good laughing together," he says. "It might predispose these small groups of people to be a more cohesive unit and consequently be more likely to survive under harsh conditions. As a behavioral mechanism, it might have had consequences on just the probability of a group of people surviving. Over multiple generations, that becomes more engrained."