Biology 202
2002 Second Paper
On Serendip

"Analyzing humor is like dissecting a frog. Few people are interested and the frog dies of it." --E. B. White

Why do people laugh? Laughter is contagious and therapeutic. It helps us cope with stress, and relax with friends. It is an indication of happiness, the sole reason we go on living. But what causes people to laugh? People laugh at jokes, semantic humor, which relies on cognitive ability to process the "humor" therein, or sometimes at slapstick type behavior requiring no intellectual understanding. People laugh at different things and for different reasons, and for the few that are interested at the expense of the frog, it can be interesting to investigate.

Every individual varies in their neurological pathways through their "boxes" in their brain to reach the output of laughter from a number of different inputs. Laughter is caused by certain visual or audio stimuli, often by perception of the unexpected or the incongruous. A surprise in expected input can result in an emotional change, however major or minor. As H. Spencer says in his Physiology of Laughter, "the nervous system in general discharges itself on the muscular system in general: either with or without the guidance of the will" (1). Incongruous input causes an emotional change, and in the case of humorous response, resulting in the contraction of facial muscles and certain muscles in the abdomen. The epiglottis half closes the larynx, resulting in giggling, guffawing, or gasping, and tear ducts are activated. These outputs of the nervous system we refer to as laughter can be arrived at through a number of pathways through the boxes of the brain, fabricated in each individual throughout their life to that point.

Although different parts of the brain are involved in understanding different types of input necessary for the laughter output, the median ventral prefrontal cortex is a key player in the physical response. Using functional magnetic resource imaging, scientists at the Institute of Neurology in London scanned the brains of people listening to jokes, and found that for example, semantic jokes, playing on the meaning of words, activate the posterior temporal lobe, and puns, which work with the sound of words, activate the left inferior prefrontal cortex. At any rate, however the input is initially processed to be found incongruous with normal expectations, the median ventral prefrontal cortex is signaled to handle the response. This area is incidentally also involved in the reward system in humans and primates, explaining why humor and laughter are enjoyable and continue to be sought as a form of entertainment (2).

Primates laugh too? As Robert R. Provine puts it, "chimpanzee laughter has the sound and cadence of a handsaw cutting wood," explaining why one might not recognize the laughter responses of animals (3). Furthermore, the laughter response of rats is merely an ultrasonic chirp (4). Animals lack the cognitive complexity that humans possess, restricting the less advanced, such as rats, to laughter induced only by tickling. However, the rats that chirped most were also the most eager to be tickled (4). This corroborates allegations that the reward system of the prefrontal cortex is responsible for the enjoyment of laughter. This reward system is involved in the compulsion to continue all enjoyable activities, invoking through desire those activities necessary for life, such as eating and sex, and entreating others that are unnecessary, such as drug addiction. In any case, the reward system relies on the release of dopamine in the prefrontal cortex, a pleasure-inducing neurotransmitter (5). This pathway is activated by a reward stimulus, and in the case of personal amusement, the reward stimulus is something that causes the subject to laugh.

Reward stimuli vary in humans, due to our increasingly complex intrinsic variability compared to those of primates and rats. An interesting example is the concept of contagious laughter, where the response activity in the brain is not the prefrontal cortex, but the anterior motor cortex and the nucleus accumbens, an area also associated with the reward system (6). Although no typically unexpected stimuli are present, the laughter continues. The anterior motor cortex and nucleus accumbens are not responsible for processing "funny" information anyway, they are merely acting as pawns of the reward system in this case, and this may explain the addictive nature of the laughter reward.

Laughing has various causes, but in general, stimuli incongruous with the expected input cause the majority of responses. This type of input doesn't always cause laughter, however. Unexpected events or stimuli can cause either 1) acute stress, if the implications are negative, or 2) humorous response, if the significance is negligible. Stress is dealt with in a number of ways, but the primary physical responses to relieve stress are laughing and crying. Both are completely natural responses and relieve the muscle tension caused by stress. Although it is understandable that one would prefer to laugh than cry for obvious reasons, there are also biological benefits to laughing for stress relief. Laughter boosts endorphins, and causes the reduction of certain neuroendocrine hormones: epinephrine, cortisol, dopac, and growth hormone, all of which are part of the body's stress response. For example, during stress, the adrenal gland releases corticosteroids, converted to cortisol in the bloodstream, which has an immunosuppressive effect. The experience of laughing lowers cortisol levels in the bloodstream and consequently boosts T-cell activity (7).

We know what parts of the brain are involved in laughter and what it can do biologically and neurologically. We know laughter requires external input or internal realizations, since is impossible to laugh on cue--making laughter one of the few physical actions humans cannot will themselves to sincerely perform. The origins of laughter are primitive and still largely not understood, but its benefits are many, and unmistakably clear.

References

1)H. Spencer: Physiology of Laughter,

2)Where in the brain is the funny bone?,

3)Robert Provine: Laughter,

4)The Biology of Humor: The Laughter Circuit,

5)The Reward Pathway,

6)Finding the Brain's Funny Bone,

7)Stress Management and Causes of Stress,


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