Biology 202
2004 Second Web Paper
On Serendip

A sign on a repair shop door in England says: We can repair anything. (Please knock hard on the door - the bell doesn't work) (1).

Did you laugh? If you did you just expended calories, lowered your blood pressure, and increased the number of immune response cells in your blood. You unconsciously triggered a neural circuit in the brain which resulted in the physical response of laughter. Laughter is an unconscious behavioral response that results from complex interactions in the brain as a result of a stimulus which we deem to be "funny." The implications of laughter, however, extend much further than expressions of enjoyment. Laughter is a cultural mechanism that has evolved from the need for members of the same species to get along. It is an example of how the unconscious workings of the brain have an effect on the conscious workings of our lives.

Ernst Haeckel, a German Evolutionist, referred to laughter as a kind of reflex or response to "psychological tickling" in which vasomotor nerves were stimulated by either a physical or mental stimulus (2). Modern scientists have made further discoveries regarding the workings of the human brain during laughter, but the general idea that laughter is an uncontrollable response to some kind of mental stimulus remains. Laughter has been found to result from a signal that travels through a loop of connected neurons located in various regions of the brain. Studies have been done that monitor these electrical signals in the brain (3). If enough voltage occurs to create an action potential, the wave of activity will travel through different regions of the brain and will result in a laugh.

Laughter is a combination of three ideas, the intellectual "getting" of something humorous, the emotional response, and the physical response of laughter (3). The main part of the brain responsible for the correct interpretation of a joke is the frontal lobe. People with damaged frontal lobes don't laugh or smile as much when shown humorous material and when given a test, often choose the wrong punch line to a written joke (4). Emotional interpretation of something humorous occurs mainly in the limbic system of the brain. This system is composed of several different parts which enable it to serve as the emotional center of the brain. The hypothalamus, in particular, deals with expressions of emotion such as laughter (5). The motor response of laughter occurs in the motor cortex, which sends signals to various muscles of the face and body. The link between the motor cortex and the brain was inadvertently discovered while testing an epilepsy patient. When the motor area was stimulated, the patient would smile or laugh uncontrollably (6).

These three portions of the brain that deal with the three aspects of intellectual comprehension, emotional response, and physical response work together to create what we know as laughter. The instigation of this event, however, is not under our conscious control. It is very difficult for one to laugh on cue without a stimulus, and there are several instances of pathological laughter in which the subject laughs without the intent (7). The most cited example of uncontrollable laughter was an epidemic which occurred in 1962 in Tanganyika and lasted for six months (2). Laughter can also be brought on by non-humorous stimuli such as laughing gas or alcohol (7). The fact that laughter can occur unconsciously through these neural circuits is significant. It implies that it is not necessarily a highly cognitive function and may have a more basic purpose.

Laughter is not only found in humans. Behavior similar to laughter can be observed in other mammals as well. Scientists have identified laugh-like behavior in rats at play. High-pitched vocalizations can be elicited by tickling and seem to indicate whether the rat is playing or fighting. Puppies are also known for a kind of laughing when they play. If a young dog lacks the ability to laugh, its actions will be interpreted as aggressive and it will get beaten up (2). Laughter, in this way, is a tool for survival. Chimpanzees and apes also exhibit laughter. It is not the definitive "ha ha ha" of the human, but more of a breathless panting noise. They produce this noise only in positive social situations such as physical play or tickling (7). Observing laughter in other species indicates that laughter seems evolved as a method of determining friend from foe.

Humans take laughter to another level of sophistication from our biological ancestors. Other animals maintain the limbic system and motor areas of the brain, but lack the highly developed cortex which enables humans to perform more analytical processes. Instead of primarily responding to physical stimuli, humans also respond to stimuli that are visual or aural. The primary purpose of laughter, however, remains the same in both humans and other mammals. It is a form of communication that encourages social bonding amongst the species.

Laughter begins to develop at a very young age, between three and four months. It is a way in which a baby can communicate without using words (8). As development occurs, laughter is used during everyday speech as punctuation. It sends an additional message to those around us that we are in a good mood and want to "play." Laughter is most often heard in groups of children as they learn how to get along and work with each other (8). Adults continue to use laughter in social situations, improving relationships with those around them. People are 30 times more likely to laugh in groups than when alone and less than 20% of what we laugh at is pre-determined jokes. Most of the things we find funny are simple everyday phrases (7). Using laughter evokes trust and works to inhibit the fight-or-flight response (1).

Have you ever found yourself laughing for no apparent reason just because someone near you is also laughing? This is because laughter can be quite contagious. Some scientists believe that humans possess some kind of laugh detector which is triggered by particular species-specific vocalizations. This detector acts as a sensory receptor and sets off the serious of neurons which results in laughter (7). The contagiousness of laughter lends itself to social bonding. When we laugh with someone, we feel instantly at ease. People often laugh in nervous situations in order to make others feel more comfortable.

Laughter has a great impact on social dynamics. Scientific observations have concluded that women laugh more than men and they laugh the most when in the presence of men (7). Also, in the office the boss tends to laugh more than the employees and when employees laugh, it is generally in response to a joke told by the boss (2). Laughter, in this way can be used to manipulate and control a relationship. Although most of its effect is positive, laughter can also be used to exclude or alienate. If a person is socially ridiculed or laughed at they might feel the need to either conform to or leave a particular group (1).

It is clear that laughter has a great impact on our lives. It enables us to build or maintain relationships by releasing social tension. What is significant about laughter is the fact that it is an unconscious response to our social situations. It is an example of one of the many little rules which work together to allow the complicated emergent system of culture to operate. It demonstrates just how little conscious control we have over our lives, and stresses the close ties between brain and behavior.

References

1)LOL website, website dedicated to the health benefits of laughter
2)Our Ancient Laughing Brain by Sylvia H. Cardoso , about the evolution of laughter
3)How Laughter Works , general overview of how laughter works
4)Brain Briefing "Humor, Laughter, and the Brain, 2001 Society for Neuroscience newsletter
5)"Limbic System: Center for Emotions", by Júlio Rocha do Amaral, MD and Jorge Martins de Oliveira, MD, PhD. Overview of the limbic system and how it effects emotions
6)"Scientists Find Sense of Humor" , from BBC News Feb. 1998
7)"Laughter" , American Scientist article by Robert Provine from 1996
8)"A Big Mystery: Why Do We Laugh?", MSNBC article by Robert Provine from 1999


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