Touch cue. Tickle is a tingling, tactile sensation, considered both pleasant and unpleasant, which results in laughter, smiling, and involuntary twitching movements of the head, limbs, and torso.
Usage I: Tickling, a playful cue, is often seen in child-child, parent-child, and male-female (i.e., courting) pairs. Its harmless-seeming, "unserious" nature has made tickling an ideal form of communication in courtship's fourth (or touch) phase. The two tickle types are a. knismesis (a light tickle which may or may not produce laughter), and b.gargalesis (a heavy tickle which usually produces the laugh response). Examples of light tickle include touching the sole of the foot with a feather, and feeling a fly walk about on one's knee. An example of heavy tickling is indenting the skin of another's ribs or waist with one's poking fingertips. (N.B.: In the Middle Ages prolonged tickling was used as a form of torture.)
Usage II: Tickling produces laughter, which releases euphoria-promoting brain chemicals, such as endorphin, enkephalin, dopamine, noradrenaline, and adrenaline. Mutual laughter stimulated by tickling can promote bonding and strengthen emotional ties. Tickling reinforces psychological closeness through the physical medium of touch. Tickling the neck, armpits, and sides of the abdomen may also arouse sexual feelings, as it stimulates nonspecific erogenous areas of the skin.
Word origin. "Tickle" comes from Middle English tikelen, "to touch lightly."
Consumer product. Tickle Me ElmoÃ‚Â® ". . . laughs and shakes when tickled. Tickle Elmo once to make him giggle. Tickle him a second time to make him laugh longer. Tickle Elmo a third time to make him shake and laugh uncontrollably. There is an auto shut-off for longer battery life (batteries included)" (Plush Elmo ad by Fisher Price).
RESEARCH REPORTS. While the philosophers Plato and Aristotle speculated about tickling, the first scientific study was published in1872 by Charles Darwin.1."Everyone knows how immoderately children laugh, and how their whole bodies are convulsed, when they are tickled" (Darwin 1872:197). 2. "The anthropoid apes . . . likewise utter a reiterated sound, corresponding with our own laughter, when they are tickled, especially under the armpits" (Darwin 1872:197-98). 3. "Such movements [i.e., jerking away], as well as laughter from being tickled, are manifestly reflex actions . . . ." (Darwin 1872:198). 4. A study in Nature Neuroscience (Nov. 1998) by University College London researchers determined a. that during self-tickling, areas of the cerebellum are active (causing the anticipation of tickle cues), but b. that cerebellar areas are not active when subjects are tickled by experimenters (thus causing an emotional, surprise response).
Innateness. Recent studies suggest that, like laughter, which first appears in infants between 23 days and four months, the tickle response is innate. Studies of deaf-and-blind-born children, for example, show normal bodily responses to being tickled. Because tickle sensations travel through the same nerves as tactile impulses for pain and itch, they stimulate similar movements of tactile-withdrawal and scratching, both of which are innate as well.
Anatomy. The most ticklish areas of the body for light-tickle sensations (based on the duration of laughing and smiling) are, in order, a. underarms, b. waist, c. ribs, d. feet,e. knees, f. throat, g. neck, and h. palms. Though heavy tickling usually produces laughter, most people say they dislike being tickled.
Evolution. Tickling and breathy, laugh-like panting exhalations appear in the human being's closest primate relatives, the great apes. The primate tickle response may have evolved, in part, from the mammalian scratch reflex, which utilizes ancient vertebrate pathways for pain. The scratch reflex produces rhythmic movements of the limbs, designed to remove the irritating sources of itch stimulated, for instance, by mosquitoes and flies. Tickling a dog's abdomen produces repeated movements of the hind limb to rid the body of imagined fleas. The withdrawal response, an innate escape motion designed to remove a body part from danger, produces an involuntary movement away from a tickler's annoying fingertips.
Erogenous tickle. Like other forms of touching, tickling may stimulate sexuality as an erotic stimulus to the skin (see feet). Touching nonspecific erogenous areas of the neck, armpits, and sides of the abdomen, e.g., may produce pleasurable tickling sensations. Touching specific erogenous zones (i.e., the mucocutaneous skin of the genital regions; see LOVE SIGNALS V) may stimulate acute sexual sensations. (N.B.: Specialized mucocutaneous end-organs appear to be involved in experiencing tactile pleasure from erogenous zones.)
Neuro-notes. Tickle (and itch) sensations are produced through mild stimulation of the nerve endings (group C unmyelinated fibers) for pain (i.e., group C unmyelinated fibers). As noted above, heavy tickling by oneself of one's own body does not lead to laughter. Imaging studies suggest that the brain's cerebellum anticipates the tickling movements, and thus unconsciously nullifies the required element of surprise. The reason human beings laugh while being tickled is still unknown. Tickle's laughter may be prompted by a neural link between vocalizing and grooming in the cingulate gyrus of the mammalian brain.
Drawing of "Showing My Nonverbal Side" by my son Aaron Huffman (copyright 2012 by Aaron M. Huffman)