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Tickling is the act of touching a part of the body, so as to cause involuntary twitching movements or laughter. Such sensations can be pleasurable or exciting, but are sometimes considered highly unpleasant, particularly in the case of relentless heavy tickling.
In 1897 psychologists G. Stanley Hall and Arthur Allin described a "tickle" as two different types of phenomena. The first is a sensation caused by very light movement across the skin. This type of tickle, called knismesis, generally does not produce laughter and is sometimes accompanied by an itching sensation. The second type of tickle is the laughter inducing, "heavy" tickle, produced by repeatedly applying pressure to "ticklish" areas, and is known as gargalesis.
The feather-type of tickle is often elicited by crawling animals and insects, such as spiders, mosquitoes, scorpions 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 fibers 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 fibers 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. Further studies have discovered that when the pain nerves are severed by surgeons, in an effort to reduce intractable pain, the tickle response is also diminished. However, in some patients that have lost pain sensation due to spinal cord injury, some aspects of the tickle response do remain. Tickle may also depend on nerve fibers associated with the sense of touch. When circulation is severed in a limb, the response to touch and tickle are lost prior to the loss of pain sensation.
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, and midriff, especially 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.
 Social aspects
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 you cannot effectively tickle yourself.
Tickling is defined by many child psychologists as an integral bonding activity between parents and children. In the parent-child concept, tickling establishes at an early age the pleasure associated with being touched by a parent with a trust-bond developed so that parents may touch a child, in an unpleasant way, should circumstances develop such as the need to treat a painful injury or prevent harm from danger. This tickling relationship continues throughout childhood and often into the early to mid teenage years.
Another tickling social relationship is that which forms between siblings of relatively the same age. Many case studies have indicated that siblings often use tickling as an alternative to outright violence when attempting to either punish or intimidate one another. The sibling tickling relationship can occasionally develop into an anti-social situation, or “tickle-torture”, where one sibling will tickle the other, without mercy. The motivation behind tickle-torture is often to portray the sense of domination the tickler has over the "ticklee".
As with parents and siblings, tickling serves as a bonding mechanism between friends, and is classified by psychologists as part of the fifth and highest grade of social play which involves special intimacy or “cognitive interaction”. This suggests that tickling works best when all the parties involved feel comfortable with the situation and one another. During adolescence, tickling often serves as an outlet for sexual energy between individuals, with erotic games, foreplay and sex becoming the motivation of the tickler. The body openings and erogenous zones are extremely ticklish; however, the tickling of these areas is generally not associated with laughter or withdrawal.
While many people assume that other people enjoy tickling, a recent survey of 84 college students indicated that only 32% of respondents enjoyed being tickled (32% and 36% of respondents, respectively, either gave neutral responses, or stated that they did not enjoy being tickled.). In the same study the authors found that those people who indicated that they did not enjoy being tickled actually smiled more often during tickling than those who did enjoy being tickled, which confirms that the usual association between smiling and pleasure is broken in the context of unpleasant tickling.
Excessive tickling has been described as a primary sexual obsession and, under these circumstances, is sometimes considered a form of paraphilia. Tickling can also be a form of, or simply be mistaken for, sexual harassment.
 Purpose of tickling
Many of history's greatest thinkers have pondered the mysteries of the tickle response, including Plato, Francis Bacon, Galileo and Charles Darwin. Many scientists have followed in their footsteps and have ventured opinions and hypotheses that attempt to explain the nearly ubiquitous nature of the tickle response.
One hypothesis, as mentioned above, is that tickling serves as a pleasant bonding experience between parent and child. However, this hypothesis does not adequately explain why many children and adults find tickling to be an unpleasant experience. 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.
It is unknown why certain people find areas of the body to be more ticklish than others; additionally, studies have shown that there is no significant difference in ticklishness between the genders. 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.
To understand how much of the tickle response is dependent on the interpersonal relationship of the parties involved, Christenfeld and Harris presented subjects with a "mechanical tickle machine". They found that the subjects laughed just as much when they believed they were being tickled by a machine as when they thought they were being tickled by a person. Harris goes on to suggest that the tickle response is reflex, similar to the startle reflex, that is contingent upon the element of surprise.
Knismesis may in fact 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. One known way is by gently touching the roof of your mouth with a fingertip.
Gargalesis, on the other hand, produces an odd phenomenon, when a person touches “ticklish” body parts on their own bodies, most people measure no tickling sensation. It is thought that the tickling requires a certain amount of surprise, and because tickling one’s self 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 him- 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. A small percentage of people however, have found it possible to tickle themselves.
 In popular culture
|Lists of miscellaneous information should be avoided. Please relocate any relevant information into appropriate sections or articles. (May 2008)|
- Trout tickling is mentioned in Shakespeare's Twelfth Night, the servant Maria refers to the approach of the hated Malvolio, head of Olivia's household, with the words "for here comes the trout that must be caught with tickling". Trout tickling is also mentioned as a poaching method in Roald Dahl's classic novel Danny the Champion of the World.
- In some science fiction literature, devices known as tickling boots are depicted as punishment-torture devices employed by some technological societies. The British science fiction show The Tomorrow People featured tickling boots in the episode A Man for Emily. Tickling boots also appeared in several short story-plays on the Nickelodeon program Kids Writes.
- In the 1960s era comic book Magnus: Robot Fighter there is one instance of a weather control tower producing "Tickle Rain". People hid under transparent plastic domes that had handles on the inside, so that the first people who managed to get under the domes could hold the domes down from the inside and then watch the "unfortunate" others being tickled to helpless hysterics by the rain drops.
- In H. P. Lovecraft's short novel The Dream Quest of Unknown Kadath the author describes nightgaunts—ebony-skinned, faceless, flying creatures that guard forbidden places from trespassers. When disturbed, the nightgaunts carry their victims away to unpleasant fates, tickling the poor captives into submission on the way. The more the captive struggles, the more he is tickled.
- In the VeggieTales episode Esther... The Girl Who Became Queen, which is based on the stories of the Biblical Book of Esther, instead of being executed by hanging—as described in the biblical book—offenders were instead exiled to 'The Island of Perpetual Tickling'.
- In the popular 1987 cartoon Teenage Mutant Ninja Turtles, a minor villain named Don Turtelli, would frequently use tickling as a form of interrogation. When capturing a hostage, his normal procedure would be to tie the victim to a chair, bare feet propped up, and tickle the soles of their feet with a feather until the hostage told him what he wanted to know.
- A Star Trek audio story for children, entitled "To Starve a Fleaver", released in the 1970s and written by Alan Dean Foster, told the tale of the Starship Enterprise becoming infested with tiny parasites called meegees, which instead of drinking blood, feed on mirth expressed by their hosts. When a host isn't happy, the meegees move around and tickle their hosts to get them to laugh.
- In the SpongeBob SquarePants episode Mermaid Man and Barnacle Boy III, the villain Man Ray is kept from performing evil acts by a tickle belt.
- In an episode of Nickelodeon's My life as a Teenage Robot The main character xJ9 or Jenny, the crime fighting teenage robot, becomes aware of tickling and that she is unaffected. When she sees the joy of her friends' tickle fights, she acquires tickle nerve endings to apply to her robotic form. She soon finds that the nerve endings ultimately disrupt her crime fighting and she soon finds the need to abandon them. All though at the end of the episode it reveals that she kept one tickle nerve ending on her underarm so she can enjoy the sensation of a tickle when she so pleases.
 See also
- ^ Etymology of "tickle"
- ^ Hall, G. S., and A. Allin. 1897. The psychology of tickling, laughing and the comic. The American Journal of Psychology 9:1-42.
- ^ Panksepp J, Burgdorf J (2003). ""Laughing" rats and the evolutionary antecedents of human joy?". Physiol. Behav. 79 (3): 533–47. doi:10.1016/S0031-9384(03)00159-8. PMID 12954448.
- ^ Zotterman, Y. 1939. Touch, pain and tickling: An electrophysiological investigation on cutaneous sensory nerves. Journal of Physiology 95:1-28.
- ^ Lahuerta J, et. al (1990). "Clinical and instrumental evaluation of sensory function before and after percutaneous anterolateral cordotomy at cervical level in man". Pain 42 (1): 23–30. doi:10.1016/0304-3959(90)91087-Y. PMID 1700355.
- ^ Nathan PW (1990). "Touch and surgical division of the anterior quadrant of the spinal cord". J. Neurol. Neurosurg. Psychiatr. 53 (11): 935–9. PMID 2283523.
- ^ a b c d e f Harris, Christine R. The mystery of ticklish laughter. American Scientist. July-August 1999 v87 i4 p344(8).
- ^ Newman B, O'Grady MA, Ryan CS, Hemmes NS (1993). "Pavlovian conditioning of the tickle response of human subjects: Temporal and delay conditioning". Perceptual and Motor Skills 77 (3 Pt 1): 779–85. PMID 8284153.
- ^ Darwin, C. 1872/1965. The Expressions of the Emotions in Man and Animals. London: John Murray.
- ^ a b c d e Fagen R. The future of play theory. A multidisciplinary inquiry into the contributions of Brian Sutton-Smith. Albany NY: SUNY Press; 1995. p22-24.
- ^ a b Michael Moran, Erotic Tickling, Greenery Press, 2003. ISBN 1-890159-46-8.
- ^ Freud S. Three contributions to the theory of sex. In: The basic writings of Freud. New York: Modern Library; 1938.
- ^ a b c Selden ST (2004). "Tickle". J. Am. Acad. Dermatol. 50 (1): 93–7. doi:10.1016/S0190 (inactive 2008-06-28). PMID 14699372.
- ^ a b Harris C.R. and Nancy Alvarado. 2005. Facial expressions, smile types and self-reporting during humour, tickle and pain (pdf). Cognition and Emotion. 9(5),655-669.
- ^ Ellis H. Studies in the psychology of sex. Vol iii. Philadelphia: FA Davis Co.; 1926
- ^ Simpson JY. On the attitude of the fetus in utero. Obstetric Memoirs, vol ii. Philadelphia: Lippincott; 1855-1856.
- ^ Weinstein, S. 1968. Intensive and extensive aspects of tactile sensitivity as a function of body part, sex, and laterality. In The Skin Senses, ed. D. R. Kenshalo. Springfield, Ill.: Thomas. pp. 195-222.
- ^ Black DW (1984). "Laughter". JAMA 252 (21): 2995–8. doi:10.1001/jama.252.21.2995. PMID 6502861.
- ^ Harris, C. R., and N. Christenfeld. In press. Can a machine tickle? Psychonomic Bulletin and Review.
- ^ Blakemore SJ, Wolpert DM, Frith CD (1998). "Central cancellation of self-produced tickle sensation". Nat. Neurosci. 1 (7): 635–40. doi:10.1038/2870. PMID 10196573.
 Further reading
- Carlsson K, Petrovic P, Skare S, Petersson KM, Ingvar M (2000). "Tickling expectations: neural processing in anticipation of a sensory stimulus". Journal of Cognitive Neuroscience 12 (4): 691–703. doi:10.1162/089892900562318. PMID 10936920.
- Fried I, Wilson CL, MacDonald KA, Behnke EJ (1998). "Electric current stimulates laughter". Nature 391 (6668): 650. doi:10.1038/35536. PMID 9490408.
- Fry WF (1992). "The physiologic effects of humor, mirth, and laughter". JAMA 267 (13): 1857–8. doi:10.1001/jama.267.13.1857. PMID 1545471.
 External links
- Telegraph (UK) Article on "robot tickling experiment"
- Boston Globe Online - Why are some people not ticklish?
- Article 'Is it possible for someone to be tickled to death?' from The Straight Dope