Daily Mail

Why CAN’T you tickle yourself?

It’s one of Nature’s quirks. And the science behind it has fascinated everyone from Aristotle to Freud

- By Antonia Hoyle

TICKLING can give babies their first giggle, lull a trout into a trance and prove erotic enough a distractio­n to lure a lady away from her good intentions. Yet it remains a bizarre and baffling phenomenon — loathed or loved — which continues to intrigue the best minds in science.

earlier this month, research published in the science journal consciousn­ess And cognition revealed that — contrary to experts’ previous understand­ing, that has stood since Greek philosophe­r Aristotle laid claim to the subject — it is possible for some people to tickle themselves.

here we investigat­e the science behind the sensation.

WHY ARE WE TICKLISH?

TICKLING happens when the skin’s nerve endings are stimulated, sending a message through the nervous system to two separate regions of the brain: the somatosens­ory cortex, the area primarily responsibl­e for analysing touch, and the anterior cingulated cortex, an area towards the front of the brain that controls emotion. combined, this creates the tickle sensation.

TWO TYPES OF TICKLE

There are actually two types of tickles: knismesis and gargalesis. The former is associated with low levels of stimulatio­n to sensitive parts of the body, and can be triggered by a light touch or by a light electric current.

Knismesis can also be triggered by crawling insects or parasites, prompting scratching or rubbing at the ticklish spot, thereby removing the pest.

‘Fortunatel­y, our brains have evolved to block our response to the sensation when we are able to predict what it will feel like — otherwise something as simple as putting on our socks would turn us into a nervous wreck,’ says Dr emily Grossman, an expert in molecular biology

Gargalesis refers to harder, laughter-inducing tickling, and involves the repeated applicatio­n of high pressure to sensitive areas.

SENSITIVE SPOTS

The soles of the feet are most people’s peak tickle spots because they are filled with highly sensitive nerve receptors. The armpits — another ticklish area — have numerous veins and arteries that make them extra sensitive.

Our most ticklish zones are coincident­ally our weakest spots, such as the neck and stomach, and evolutiona­ry biologists believe we laugh when these areas are touched as a defence mechanism to signal submissive­ness.

‘research suggests that laughter is an instinctiv­e response to protect us,’ says Dr Grossman. ‘We’re showing we’re not a threat. It is a way of diffusing the situation.’

BABY BANTER

NEUROSCIEN­TISTS believe tickling to be an important form of pre-verbal communicat­ion. It allows babies to create a distinctio­n between themselves and others and can be a bonding activity between parent and child that also helps establish a relationsh­ip of trust. ‘Tickling can provide a social function to connect us to loved ones,’ says Dr Grossman. ‘It makes us feel good because physical touch releases happy hormones such as oxytocin and dopamine, as does the laughter that tickling triggers.’

Tickling often continues throughout childhood between siblings, as a way for younger teenagers to assert their dominance over one another and resolve arguments without resorting to violence.

DEGREES OF TICKLY

EVERYONE with functionin­g nerve- endings is susceptibl­e to the sensation of being tickled, but, as irritating as it is for anyone who recalls losing out to a sibling in a tickle- off during childhood, some of us are better at sensing when we are about to be tickled than others, prompting the cerebellum — the part of the brain that predicts the sensory consequenc­es of movements — to block the rest of the brain’s response to the tickle.

WHY CAN’T I TICKLE MYSELF?

BECAUSE tickling only works when you aren’t expecting it, most people cannot tickle themselves.

‘As our hand moves towards our skin the cerebellum can make its own accurate prediction of what it will feel like which blocks the brain’s response,’ says Dr Grossman.

‘simply watching someone else’s hand coming towards us isn’t enough to predict how it’s going to feel. but if you touch someone’s hand as they’re about to tickle you it will allow you to block the sensation as if it were your own hand and stop it tickling.’

... OR CAN I?

HOWEVER, the scientists whose findings were published in consciousn­ess And cognition discovered that those displaying schizophre­nic tendencies — such as erratic behaviour and the inability to derive pleasure from social experience­s — are more likely to be able to tickle themselves.

researcher­s at the university of Lille in France selected people with schizophre­nic traits to both tickle and tickle themselves.

It emerged they didn’t find self-tickling to be any less ticklish than being tickled by a third party.

This is believed to be because the process that tells the brain that the act of self-tickling is voluntary is impaired in such people, so they are more likely to react as if the tickle was from an external cause or person.

NO LAUGHING MATTER

WHILE some undoubtedl­y enjoy the sensation of tickling, the action activates a part of the brain that controls facial movement called the rolandic operculum, making you laugh even if you’re not really having good time at all.

One recent survey found 36 per cent of people actively disliked the sensation of being tickled — and for those who aren’t fans it can be frightenin­g and painful — so much so that it was used as a form of torture by Nazi prison guards during World War II.

TICKLED TO DEATH

‘A PHOBIA of tickling is quite rare — but understand­able,’ says Dr sandi mann, senior psychology lecturer at the university of central Lancashire. ‘sufferers fear the lack of control that comes from being tickled and the inability to articulate their fear because they are struggling to breathe. For them the saying “tickled to death” is a truly scary concept.’

Tickle phobias are likely to be triggered by an event in childhood, from a tickling incident to some sort of boisterous horseplay. Dr mann says: ‘Treatment would involve gradual exposure to tickling to desensitis­e the sufferer.’

TICKLE THROUGH TIME

The phenomenon has long troubled philosophe­rs, and until the 19th century it was widely believed tickling and humour were linked.

charles Darwin and psychiatri­st ewald hecker consolidat­ed this theory with the Darwin-hecker hypothesis that stated humans would only laugh when tickled if in a good mood .

SLAP AND TICKLE

SIGMUND Freud was fascinated by tickling and sex as part of his pleasure-pain principle. he wrote a lot about the ‘rhythm ’ and the ‘rises and falls in the quantity of stimulus’ in types of tickling.

sex expert Lucy Jones says the neck, shoulder and back are among the most popular erogenous zones for lovers to tickle one another.

‘Not only does tickling release feelgood hormones that help us bond with our partner, it serves as an introducti­on to a physical relationsh­ip; a comforting way of exploring our bodies without being overtly sexual,’ she says.

ANIMAL KINGDOM

ARISTOTLE’s theory that only humans are intelligen­t enough to respond to tickling is not strictly true: some animals rely on knismesis to help them shake off other animals or insects that are a threat.

horses shudder to get flies off their backs. Trout, meanwhile, go into a trance when rubbed on their underbelly, as do rabbits when turned on their backs and tickled on their chest.

‘It is a stress response among prey species,’ explains animal behaviouri­st Dr huw stacey. ‘The rabbit is keeping still because it is scared, not because tickling is enjoyable.’

Gargalesis is experience­d by chimps, gorillas and orangutans, our closest primate relatives. The only other animal proven to respond to this type of tickling is, bizarrely, the rat. Neuroscien­tist Jaak Panksepp found the rodents emit highpitche­d noises — a laugh — in response to being tickled.

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