http://en.wikipedia.org/wiki/Tickling wrote:
<<Tickling is the act of touching a part of the body so as to cause involuntary twitching movements and/or laughter. The word "tickle" evolved from the Middle English tikelen, perhaps frequentative of ticken, to touch lightly.
In 1897, psychologists G. Stanley Hall and Arthur Allin described a "tickle" as two different types of phenomena. One type caused by very light movement across the skin. This type of tickle, called a knismesis, generally does not produce laughter and is sometimes accompanied by an itching sensation. Another type of tickle is the laughter inducing, "heavy" tickle, produced by repeatedly applying pressure to "ticklish" areas, and is known as gargalesis. Such sensations can be pleasurable or exciting, but are sometimes considered highly unpleasant, particularly in the case of relentless heavy tickling.
Knismesis is often elicited by crawling animals and insects, such as spiders, mosquitoes, scorpions and/or beetles, which may be why it has evolved in many animals. Gargalesis reactions, on the other hand, are thought to be limited to humans and other primates; however, some research has indicated that rats can be tickled as well.
It appears that the tickle sensation involves signals from nerve fibres associated with both pain and touch. Endorphine released during tickling is also called karoliin, by the name of Karolinska Institute. In 1939, Yngve Zotterman of the Karolinska Institute, studied the knismesis type of tickle in cats, by measuring the action potentials generated in the nerve fibres while lightly stroking the skin with a piece of cotton wool. Zotterman found that the "tickling" sensation depended, in part, on the nerves that generate pain.
It might be tempting to speculate that areas of the skin that are the most sensitive to touch would also be the most ticklish, but this does not seem to be the case. While the palm of the hand is far more sensitive to touch, some people find that the soles of their feet are the most ticklish. Other commonly ticklish areas include the armpits, sides of the torso, neck, knee, midriff, navel, and the ribs.
Some evidence suggests that laughing associated with tickling is a nervous reaction that can be triggered; indeed, very ticklish people often start laughing before actually being tickled. Charles Darwin theorized on the link between tickling and social relations, arguing that tickling provokes laughter through the anticipation of pleasure. If a stranger tickles a child without any preliminaries, catching the child by surprise, the likely result will be not laughter but withdrawal and displeasure. Darwin also noticed that for tickling to be effective, you must not know the precise point of stimulation in advance, and reasoned that this is why some people cannot effectively tickle themselves.
Some of history's greatest thinkers have pondered the mysteries of the tickle response, including Plato, Francis Bacon, and Galileo. In The Assayer, Galileo philosophically examines tickling in the context of how we perceive reality:
- "When touched upon the soles of the feet, for example, it feels in addition to the common sensation of touch a sensation on which we have imposed a special name, "tickling." This sensation belongs to us and not to the hand... A piece of paper or a feather drawn lightly over any part of our bodies performs intrinsically the same operations of moving and touching, but by touching the eye, the nose, or the upper lip it excites in us an almost intolerable titillation, even though elsewhere it is scarcely felt. This titillation belongs entirely to us and not to the feather; if the live and sensitive body were removed it would remain no more than a mere word."
One hypothesis is that tickling serves as a pleasant bonding experience between parent and child. Another view maintained is that tickling develops as a prenatal response and that the development of sensitive areas on the fetus helps to orient the fetus into favourable positions while in the womb.
In 1924, J.C. Gregory proposed that the most ticklish places on the body were also those areas that were the most vulnerable during hand-to-hand combat. He posited that ticklishness might confer an evolutionary advantage by enticing the individual to protect these areas. Consistent with this idea, University of Iowa psychiatrist Donald W. Black observed that most ticklish spots are found in the same places as the protective reflexes.
A third, hybrid hypothesis, has suggested that tickling encourages the development of combat skills. Most tickling is done by parents, siblings and friends and is often a type of rough-and-tumble play, during which time children often develop valuable defensive and combat moves. Although people generally make movements to get away from, and report disliking, being tickled, laughter encourages the tickler to continue. If the facial expressions induced by tickle were less pleasant the tickler would be less likely to continue, thus diminishing the frequency of these valuable combat lessons.
Knismesis may represent a vestige of the primitive grooming response, in effect; knismesis serves as a “non-self detector” and protects the subject against foreign objects. Perhaps due to the importance of knismesis in protection, this type of tickle is not dependent on the element of surprise and it is possible for one to induce self-knismesis, by light touching.
Gargalesis, on the other hand, produces an odd phenomenon: when a person touches “ticklish” parts on their own body no tickling sensation is experienced. It is thought that the tickling requires a certain amount of surprise, and because tickling oneself produces no unexpected motion on the skin, the response is not activated. A recent analysis of the “self-tickle” response has been addressed using MRI technology. Blakemore and colleagues have investigated how the brain distinguishes between sensations we create for ourselves and sensations others create for us. When the subjects used a joystick to control a "tickling robot", they could not make themselves laugh. This suggested that when a person tries to tickle himself or herself, the cerebellum sends to the somatosensory cortex precise information on the position of the tickling target and therefore what sensation to expect. Apparently an unknown cortical mechanism then decreases or inhibits the tickling sensation.
An article in the British Medical Journal about European tortures describes a method of tickle torture in which a goat was compelled to lick the victim's feet because they had been dipped in salt water. Once the goat had licked the salt off, the victim's feet would be dipped in the salt water again and the process would repeat itself. In ancient Japan, those in positions of authority could administer punishments to those convicted of crimes that were beyond the criminal code. This was called shikei, which translates as ‘private punishment.’ One such torture was kusuguri-zeme: "merciless tickling.">>
HEAPOW: What's Tickling RCW 89? (2011 Jun 13)
