Laughter is an audible expression of happiness, or an inward feeling of joy. It may ensue from hearing a joke, being tickled, or other stimuli. It is in most cases a very pleasant sensation.
Laughter is found among various animals, as well as in humans. Among the human species, it is a part of human behavior regulated by the brain, helping humans clarify their intentions in social interaction and providing an emotional context to conversations. Laughter is used as a signal for being part of a group—it signals acceptance and positive interactions with others. Laughter is sometimes seen as contagious, and the laughter of one person can itself provoke laughter from others as a positive feedback. This may account in part for the popularity of laugh tracks in situation comedy television shows.
Laughter is anatomically caused by the epiglottis constricting the larynx. The study of humor and laughter, and its psychological and physiological effects on the human body, is called gelotology.
Laughter is an audible expression or appearance of excitement, an inward feeling of joy or humor. It may ensue from jokes, tickling, and other stimuli. Researchers have shown infants as early as 17 days old have vocal laughing sounds or laughter. It conflicts with earlier studies indicating that infants usually start to laugh at about four months of age. Laughter researcher Robert R. Provine said: “Laughter is a mechanism everyone has; laughter is part of universal human vocabulary. There are thousands of languages, hundreds of thousands of dialects, but everyone speaks laughter in pretty much the same way.” Everyone can laugh. Babies have the ability to laugh before they ever speak. Children who are born blind and deaf still retain the ability to laugh.
Provine argues that “Laughter is primitive, an unconscious vocalization.” Provine argues that it probably is genetic. In a study of the “Giggle Twins”, two happy twins who were separated at birth and only reunited 43 years later, Provine reports that “until they met each other, neither of these exceptionally happy ladies had known anyone who laughed as much as she did.” They reported this even though they both had been brought together by their adoptive parents, who they indicated were “undemonstrative and dour.” He indicates that the twins “inherited some aspects of their laugh sound and pattern, readiness to laugh, and maybe even taste in humor.” 
Norman Cousins suffered from arthritis and developed a recovery program incorporating megadoses of Vitamin C, along with hope, a positive attitude, and laughter induced by Marx Brothers films. “I made the joyous discovery that ten minutes of genuine belly laughter had an anesthetic effect and would give me at least two hours of pain-free sleep. When the pain-killing effect of the laughter wore off, we would switch on the motion picture projector again and not infrequently, it would lead to another pain-free interval.” 
Scientists have noted the similarity in forms of laughter among various primates, which suggests that laughter derives from a common origin among primate species.
A very rare neurological condition has been observed whereby the sufferer is unable to laugh out loud, a condition known as aphonogelia.
Neurophysiology indicates that laughter is linked with the activation of the ventromedial prefrontal cortex, that produces endorphins
Scientists have shown that parts of the limbic system are involved in laughter. This system is involved in emotions and helps us with functions necessary for human’s survival. The structures in the limbic system that are involved in laughter: the hippocampus and the amygdala.
The December 7, 1984 Journal of the American Medical Association describes the neurological causes of laughter as follows:
“Although there is no known ‘laugh center’ in the brain, its neural mechanism has been the subject of much, albeit inconclusive, speculation. It is evident that its expression depends on neural paths arising in close association with the telencephalic and diencephalic centers concerned with respiration. Wilson considered the mechanism to be in the region of the mesial thalamus, hypothalamus, and subthalamus. Kelly and co-workers, in turn, postulated that the tegmentum near the periaqueductal grey contains the integrating mechanism for emotional expression. Thus, supranuclear pathways, including those from the limbic system that Papez hypothesised to mediate emotional expressions such as laughter, probably come into synaptic relation in the reticular core of the brain stem. So while purely emotional responses such as laughter are mediated by subcortical structures, especially the hypothalamus, and are stereotyped, the cerebral cortex can modulate or suppress them.”
Laughter and health
A link between laughter and healthy function of blood vessels was first reported in 2005 by researchers at the University of Maryland Medical Center with the fact that laughter causes the dilatation of the inner lining of blood vessels, the endothelium, and increases blood flow. Drs. Michael Miller (University of Maryland) and William Fry (Stanford), theorize that beta-endorphin like compounds released by the hypothalamus activate receptors on the endothelial surface to release nitric oxide, thereby resulting in dilation of vessels. Other cardioprotective properties of nitric oxide include reduction of inflammation and decreased platelet aggregation.
Common causes for laughter are sensations of joy and humor; however, other situations may cause laughter as well.
A general theory that explains laughter is called the relief theory. Sigmund Freud summarized it in his theory that laughter releases tension and “psychic energy”. This theory is one of the justifications of the beliefs that laughter is beneficial for one’s health. This theory explains why laughter can be as a coping mechanism for when one is upset, angry or sad.
Philosopher John Morreall theorizes that human laughter may have its biological origins as a kind of shared expression of relief at the passing of danger. Friedrich Nietzsche, by contrast, suggested laughter to be a reaction to the sense of existential loneliness and mortality that only humans feel.
For example, this is how this theory works in the case of humor: a joke creates an inconsistency, the sentence appears to be not relevant, and we automatically try to understand what the sentence says, supposes, doesn’t say, and implies; if we are successful in solving this ‘cognitive riddle’, and we find out what is hidden within the sentence, and what is the underlying thought, and we bring foreground what was in the background, and we realize that the surprise wasn’t dangerous, we eventually laugh with relief. Otherwise, if the inconsistency is not resolved, there is no laugh, as Mack Sennett pointed out: “when the audience is confused, it doesn’t laugh” (this is the one of the basic laws of a comedian, called “exactness”). It is important to note that the inconsistency may be resolved, and there may still be no laugh. Because laughter is a social mechanism, we may not feel like we are in danger, however, the physical act of laughing may not take place. In addition, the extent of the inconsistency (timing, rhythm, etc.) has to do with the amount of danger we feel, and thus how hard or long we laugh. This explanation is also confirmed by modern neurophysiology (see section Laughter and the brain).
Laughter can also be brought on by tickling. Although it is found unpleasant by most people, being tickled often causes heavy laughter which is thought to be a reflex of the body, and is often uncontrollable.
Connor MacLeod, also known as The Highlander, is a fictional character in the Highlander film series, as well as the television programs Highlander: The Series, and Highlander: The Animated Series. In the films, he is portrayed by Christopher Lambert.
The character of Connor MacLeod is divided between many separate continuities; the original movie, each sequel, the television series, and the multiple animated series. Although varying from leading man to supporting character in each different continuity, Connor’s importance to each continuity’s story is not to be overlooked.
WHEN I THINK ABOUT LAUGHTER I ALWAYS GET THE McLeod sense that the laugh is a hounding type of magic that looks into the face of the truth and with the eyes of no character and then denies it
afterall Mcleod is immortal
AND THEN THE SMILE
“there can be only one”
quote: Conner McLeod
IMAGE COURTESY OF Wikipedia