Why are people ticklish?
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Tickling is perplexing to say the least. So let's tickle your fancy and dive right in. To start, there are two distinct types of tickling.
Knismesis refers to a light tickling sensation, such as when a stray hair brushes against your skin, and it does not typically induce giggling. Many other non-human species have this mechanism, and the evolutionary value is pretty straightforward: knismesis can alert you to insects crawling on your skin so you can brush them off.
Gargalesis is the type of tickling more commonly associated with humans. This is the hands-on tickling that makes you laugh and squirm, and the type of tickling we'll explore going forward. So what's happening physiologically when we're getting tickled?
Your skin contains millions of nerve endings that sense physical stimuli, such as touch and pressure. When someone tickles you, mechanoreceptors – specialized nerve endings that detect touch and pressure – send signals to your brain. Tickling is especially sensitive on areas like your sides, underarms, and feet, where mechanoreceptors are highly concentrated.
From there, signals are sent to two important areas of your brain. The somatosensory cortex interprets the physical aspects of tickling, such as pressure and location, while the anterior cingulate cortex evaluates the emotional context, like deciding if the tickling feels playful because it's coming from a friend or invasive if it's coming from a stranger.
The brain's processing of the tickling sensation also triggers certain autonomic responses including squirming and giggling. Tickling triggers reflexive movements to withdraw from the tickler, likely as a protective mechanism for sensitive areas. Interestingly, the reflexes we have when we're getting tickled are similar to someone in severe pain.
Tickling also elicits reflexive laughter, an involuntary autonomic response. Research suggests that this laughter isn't necessarily a reflection of how much fun you're having; it's likely an emotional reflex to ease the tension you're feeling. These brain-activated reflexes show that tickling seems to straddle the line between pain and pleasure.
Some people seem to be immune from the effects of tickling. The reasons why aren't fully understood, but here are the factors that have an impact on how ticklish someone is:
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