Cognitive neuroscientists at Dartmouth College have shown that the part of your brain that "gets" a joke is not the same as the region that deems it funny or not. To test their hypothesis, the researchers conducted functional magnetic resonance imaging (fMRI) on subjects while they watched Seinfeld and The Simpsons. From a Scientific American report on the study:
"The investigators found that instances of humor detection lit up the left inferior frontal and posterior temporal cortices–the left side of the brain. Humor appreciation, in contrast, led to spikes in activity in the emotional areas deeper inside–specifically, in the bilateral regions of the insular cortex and the amygdala… Past research has shown the left inferior frontal cortex to be involved in reconciling ambiguous meanings with prior knowledge. And ambiguity, incongruity and surprise are key elements in many jokes."
Still, the results are preliminary. When SciAm asked an outside psychologist for his expert opinion on the research, he commented: "If some people don't find The Simpsons funny, it's premature to say that they have a defective frontal lobe."
Of course, he's wrong. Link
