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Laughter on the Brain

­The physiological study of laughter has its own name -- gelotology. And we know that ce­rtain parts of the brain are responsible for certain human functions. For example, emotional responses are the function of the brain's largest region, the frontal lobe. But researchers have learned that the production of laughter is involved with various regions of the brain. While the relationship between laughter and the brain is not fully understood, researchers are making some progress.
For example, Derks traced the pattern of brainwave activity in subjects responding to humorous material. Subjects were hooked up to an electroencephalograph (EEG) and their brain activity was measured when they laughed. In each case, the brain produced a regular electrical pattern. Within four-tenths of a second of exposure to something potentially funny, an electrical wave moved through the cerebral cortex, the largest part of the brain. If the wave took a negative charge, laughter resulted. If it maintained a positive charge, no response was given, researchers said.
During the experiment, researchers observed the following specific activities:
  • The left side of the cortex (the layer of cells that covers the entire surface of the forebrain) analyzed the words and structure of the joke.
  • The brain's large frontal lobe, which is involved in social emotional responses, became very active.
  • The right hemisphere of the cortex carried out the intellectual analysis required to "get" the joke.
  • Brainwave activity then spread to the sensory processing area of the occipital lobe (the area on the back of the head that contains the cells that process visual signals).
  • Stimulation of the motor sections evoked physical responses to the joke.
This is different from what happens with emotional responses. Emotional responses appear to be confined to specific areas of the brain, while laughter seems to be produced via a circuit that runs through many regions of the brain. (This means that damage to any of these regions can impair one's sense of humor and response to humor, experts say.)
Read on to learn more about how the brain and laughter are connected.

The Limbic System

­When we look more closely at the areas of the brain involved with laughter, the limbic system seems to be central. The limbic system is a network of structures lo­cated beneath the cerebral cortex. This system is important because it controls some behaviors that are essential to the life of all mammals (finding food, self-preservation).
Interestingly, the same structures found in the human limbic system can also be found in the brains of evolutionary ancient animals such as the alligator. In the alligator, the limbic system is heavily involved in smell and plays an important role in defending territory, hunting and eating prey. In humans, the limbic system is more involved in motivation and emotional behaviors.

Structures in the brain's limbic system, which controls many essential human behaviors, also contribute to the production of laughter.

While the structures in this highly developed part of the brain interconnect, research has shown that the amygdala, a small almond-shaped structure deep inside the brain, and the hippocampus, a tiny, seahorse-shaped structure, seem to be the main areas involved with emotions. The amygdala connects with the hippocampus as well as the medial dorsal nucleus of the thalamus. These connections enable it to play an important role in the mediation and control of major activities like friendship, love and affection and on the expression of mood. The hypothalamus, particularly its median part, has been identified as a major contributor to the production of loud, uncontrollable laughter.
In the next section, we'll discuss what makes us laugh. 
Discovery Health

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