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Laughter can be heard during the most inappropriate times; during a funeral, without any noticeable reason, or after a very bad joke. Others may wonder why a person would laugh without what people would consider as normal stimuli for laughter. Most would consider tickling, a funny joke, or a release in tension as normal stimuli for laughter. Is a person rebelling against social boundaries and expectations or being insensitive when he or she laughs as he or she administers shocks to someone next door? Parts of the limbic system are involved in laughter. The limbic system is a primitive part of the brain that is involved in emotions and helps us with basic functions necessary for survival. The two structures in the limbic system that have been shown to play a role in laughter are the amygdala and the hippocampus. (1) The amygdala is responsible for perceiving in others and oneself, emotional or affective behaviors and feelings such as fear and anger. (2) the amygdala is connected to the hypothalamus, the trigeminal nerve, the facial nerve, the tegmental area, locus coreruleus, and laterodorsal tegmental nucleus. The sympathetic nervous system regulates bodily functions related to homeostasis and stimulation of the fight or flight response. The reticular nucleus is responsible for increased reflexes. The trigeminal nerve and the facial nerve are responsible for facial expressions of fear. The tegmental area, locus coreruleus, and laterodorsal tegmental nucleus are responsible for the activation of dopamine norepinephrine and epinephrine. (3) The hippocampus has an essential role in the formation of new memories about experienced events. (4) According to Stanford University’s newspaper researchers found giggling activated an area called the nucleus accumbens, or the NAcc. The NAcc also known as the pleasure center is involved in the rewarding feelings that follow monetary gain or the use of some addictive drugs. (5) Those with pseudobulbar palsy, gelastic epilepsy, multiple sclerosis, ALS, and some brain tumors have abnormal laughter. Pseudobulbar palsy affects the motor fibers that travel from the cerebral cortex to the lower brain stem. The signals that are sent to the hippocampus and the amygdala will be affected. This is logical since multiple sclerosis and epilepsy are caused by brain damage or motor neuron damage. (6) Brain damage can affect the mechanism of laughing as well as how much pleasure or happiness the laughter can bring. Pathological laughter and crying (PLC) leads to uncontrollable episodes of laughter, crying or both. The episodes occur without an apparent triggering stimulus or following a stimulus that should not have led the subject to laugh or cry. (7) Patients with PLC do not suffer from an emotional disorder but a mechanical disorder. The brain damage alters the way the brain wires itself for the act of laughing. When patients with PLC laugh or cry, they do not do so with the feelings that are usually associated with laughing or crying. (8) On the other hand there are those who cannot control their euphoria or sadness. “The case of a French woman who suffered from Parkinson's disease sheds more light on the association between laughter, crying and emotions. Trying to ease the symptoms of her disease, the doctors implanted electrodes in the woman's brain. This type of Apparatus sends electric pulses to the brain region that is in charge of motor activity, causing, in most patients, a significant improvement in the motor condition… after the first pulse, the patient started crying. The alarmed doctors thought they might have hurt her. But upon inquiring, the woman responded with a different explanation. "I no longer wish to live, to see anything, hear anything, feel anything. I'm fed up with life", she wept, "I'm hopeless". The doctors stopped the current right away. Then, suddenly, the woman became happy, even manic. Laughing and joking, she playfully pulled the tie of one of the doctors. A few minutes later, her normal mood was restored, as if nothing had happened. When the doctors resumed the electric current a few days later, the same scenario repeated itself.The region that was stimulated in the woman's brain was far away from the region that caused mechanical laughter in PLC cases. This time the crying and laughing were associated with emotions; the patient believed she was laughing or crying in response to something funny or sad.” (9) This demonstrates that there is a difference to just laughing and laughing because of the normal emotions that are correlated with laughter. Is there a more general explanation for inappropriate laughter? Laughter is correlated with the pleasure center of the brain, the nucleus accumbens; the more you laugh, the more pleasure you get. Is it possible for laughter to be addictive? Like any drug that gives a high, laughter can also give you a high. Does the brain realize that laughter increases the release of serotonin and forces the body to laugh? Does it somehow fool the brain into thinking things are funny when it is not, to force the body to laugh? These are questions that researchers are pondering as well. 1)The Science of Laughter. Ellen Kuwana. Neuroscience for Kids. October 15, 2001 2)University of Idaho: Amygdala 3)Wikipedia: Amygdala 4)Wikipedia: Hippocampus 5)Stanford Report 6) Pseudobulbar palsy 7) Pathological laughter and crying 8)PBS: The Secret Life of the Brain 9) PBS: The Secret Life of the Brain