Areas in the right temporal lobe (right neocortex) interpret metaphor and "get" jokes. It understands what Freud called the "primary process," the language of the unconscious, the language of poems, art, and myth. (Goleman, Daniel. The Brain and Emotional Intelligence: New Insights. p 24-28. MA: More Than Sound, 2011)
MRI studies have shown that electrical stimulation can elicit laughter. Mirthful laughter was triggered in the left superior frontal gyrus (part of the left frontal lobe of the brain, Broca’s area, involved in the initiation of human speech). The laughter was not only produced consistently with electrical stimulation of this region of the brain, but was accompanied by a sensation of merriment or mirth. One conclusion is that laughter is simply a sound that is a form of speech. Is there a time to avoid laughter? Avoid laughter if you have broken ribs and right after abdominal surgery unless you are holding a pillow against your stitches.(Fried, Itzhak, et al. Electric current stimulates laughter. Nature 391, 650. 12 February, 1998 | doi:10.1038/35536 (Source)
Human beings have the potential to develop a sense of humor and each is born with the capacity to laugh. (Padus, Emrika, et al. The Complete Guide to Your Emotions & Your Health. p 546-547. PA: Rodale Press, 1992.)
Humor processing (getting the joke and laughing) appears to involve parts of the frontal lobes and a component of the pleasure pathway, the anterior cortex of the hypothalamus. (Restak, Richard, MD. The New Brain. p 92-94. PA: Rodale, 2003.)
Subconscious contractions of skeletal muscles involved in laughing in response to a joke are controlled by the basal ganglia, three chunks of gray matter located deep within each cerebral hemisphere. (Tortora, Gerard J. and Sandra Reynolds Grabowski. Principles of Anatomy and Physiology. p 469-471. NY: John Wiley & Sons, Inc., 2003.)
Study 2003, Reiss and colleagues: the brain's mesolimbic reward center, which is responsible for the rewarding feelings that follow such events as monetary gain or cocaine use, is also activated by humor.
MRI study of brains of 16 healthy adults: used to detect areas of the brain that were activated when the subject found a cartoon funny. In addition to activating areas of the brain involved in language processing, humor also stimulated regions of the brain known as reward centers, such as the amygdala, which releases dopamine. (WebMD Medical News. Humor Activates Reward Center of the Brain.)