The Physiology of Tickling

The Science Behind Involuntary Laughter

Nov 2, 2009

The science of tickling is complex. The brain processes pleasant tickle stimuli along with sensations of pain from other neural pathways.

In a 1844 novel, Valentine Vox: The Ventriloquist, a wealthy man named Goodman is wrongly condemned to an insane asylum by greedy relatives. Goodman learns he will be interviewed by the asylum commissioners and is confident that he will be released after convincing them of his sanity. A few moments before the commissioners arrive, however, one of the keepers (who is in league with Goodman's relatives) orders the innocent man into a cell.

Once in the cell, Goodman is stripped of his clothes, forced into a straight jacket, and chained to a bed. As soon as he is secured, the keeper pulls out a feather and methodically begins to tickle Goodman's bare feet. Unable to move or escape, Goodman's veins “began to swell, and his face became black, and his eyes appeared to be in the act of starting from their sockets,” until he is reduced to madness just before the commissioners enter.

Unable to talk coherently, Goodman cannot plead his case. After the commissioners leave, the keeper chuckles and congratulates himself. He had used tickling before to make one inmate die “under the dreadful operation, while another had been struck with paralysis, and a third had been reduced to a state of idiocy.”

The physiology of tickling is complex. How can laughter be associated with feelings of pain?

Etymology and Types of Tickling

According to the Compact Oxford English Dictionary, 'tickle' is likely derived from kittle, which is a word used in a regional Scottish dialect. 'Tickle' also has roots in the Middle English word, tikelen. When used as a verb, 'tickle' means to touch lightly in such a way as to cause “itching or twitching and often laughter.”

This definition implies that there are two distinct types of tickling – one light touch that is designed to produce a tingling itchy sensation, and a heavier touch that invokes involuntary laughter. In 1897, two psychologists (G. Stanley Hall and Arthur Allin) classified both types of tickling as follows:

Hall and Allin (1897) conducted experiments on children and determined that the most ticklish areas were the soles of the feet, the underarms, around the neck, under the chin, the ribs/waist, and the cheeks.

The Dual Nature of Tickling

In Rhetoric, the Greek philosopher Aristotle discussed the duality of pleasure and pain. In its simplest sense, pleasure brings the soul into “into its normal state of being,” while pain is “the opposite.” Force is unnatural, so what is pleasant is “not forced on us.” Anything involving compulsion, “concentration, strong effort, and strain [is] necessarily painful.”

Tickling possesses this same strong duality. Many childhood memories of tickling are associated with being held down and tickled mercilessly against one's will. As Harris (1999) observed, each “succeeding generation of children independently rediscovers 'tickle torture' as an effective way to torment their playmates.” At the same time, however, children also learn to seek out tickling as a pleasurable form of “tactile contact.”

The Physiology of Tickling

The physiology of tickling also reflects this duality. Although the brain controls bodily functions, it also receives signals from the central nervous system along various neural pathways. In the diagram, skin sensations are shown as blue neural pathways, while pain sensations (both sharp and dull) are illustrated by red neural pathways.

Sensory receptors are present throughout the body. Each receptor is programmed to respond to a specific stimulus, such as smell, sound, or touch. When the skin is tickled, the sensation is transmitted along neural pathways through the central nervous system to the brain.

The somatosensory complex in the brain analyzes 'heavier' touch sensations (including pain), while 'lighter' skin sensations are funneled through the anterior cingulate cortex (Clark, 2009). Both areas work together to interpret the tickle sensation. Light tickling (knismesis) is perceived by the brain as pleasurable, while heavier tickling (gargalesis) is interpreted as painful – and possibly torturous.

Can Tickle Sensations Be Minimized or Intensified?

Research on patients with spinal cord injuries shows that tickle sensations can be minimized or intensified. For example, patients who have limb circulation cut off also lose all tickle sensitivity, even though pain sensations persist.

On the other hand, patients with spinal cord injuries often suffer unbearable pain. To give relief, surgeons may cut pain-transmitting nerve fibers. Although pain stimuli are eliminated, tickle sensations sometimes remain (Harris, 1999). Some believe that this suggests that the brain allows pleasurable stimuli to continue at critical recovery moments.

Panksepp and Burgdorf (2003) described a case involving a 16-year-old epileptic female. In order to minimize her seizures, she underwent experimental stimulation of the “frontal cortical area,” which is known to control movement. As the pre-surgical technique began, the young woman “exhibited bouts of vigorous laughter that intensified as brain stimulation intensity increased.” Thus, even without being touched, the girl experienced a powerful tickling sensation through experimental manipulation of brain areas known to process the tickle response.

The copyright of the article The Physiology of Tickling in Biology is owned by Jeffrey Willett. Permission to republish The Physiology of Tickling in print or online must be granted by the author in writing.