Stop everything you’re doing, and try to tickle yourself. Impossible, right? That's actually pretty weird when you think about it, because sometimes a touch, say, on the back of your arm, by someone else is enough to cause a laughing fit and full body shudders.
So why can’t we elicit the same response ourselves? (Not that you’d really want to, because it’d get old real fast every time you tried to scratch your own back.) Well, it’s all thanks to your cerebellum.
Before we dive into the reason why we can’t 'self-tickle', let’s first discuss what the heck tickling actually is, and why it causes our bodies to freak out sometimes.
According to neuroscientist Sarah-Jayne Blakemore from University College London in the UK, two parts of the brain are responsible for how you process tickling: the somatosensory cortex, which is responsible for perceiving touch, and the anterior cingulate cortex, which processes pleasure.
Both of these regions work together to trigger the nervous system when someone or something is tickling you. In fact, there are actually two types of tickles: gargalesis and knismesis.
Gargalesis is the type of tickling that's heavy, causing laughter and uncontrollable body movement, while knismesis is when something - like a thread from your shirt - tickles you slightly, causing you to flinch.
The weird thing is that tickling isn’t really a pleasurable feeling (for most of us) but we still laugh like we just heard the best joke in the world. Why?
According to a 2013 study by researchers from Eberhard Karls University of Tübingen in Germany, this is because both a joke and a tickle trigger a part of your brain called the Rolandic Operculum - an area responsible for vocal and emotional reactions, reports Erin McCarthy for Mental Floss.
Laughing, it turns out, is a way that our ancestors might have submitted to aggression, allowing them to survive because it helps them signal to someone stronger that they don't want to fight. Nowadays, that need is pretty much gone, but the tickle laughter still remains. Thanks, evolution!
So now that we know a little more about the physiological side of tickling, why can’t we do it ourselves? Well, it basically comes down to your cerebellum having the ability to predict the tickle, therefore cancelling it out before the sensation takes over.
"Our studies at University College London have shown that the cerebellum can predict sensations when your own movement causes them but not when someone else does," Blakemore explained to Scientific American. "When you try to tickle yourself, the cerebellum predicts the sensation and this prediction is used to cancel the response of other brain areas to the tickle."
In other words, your cerebellum - the part of your brain that monitors motor control - knows where your hand (or feather duster) is going to try to tickle. Because of this, the sensation is lost, because it’s no longer a surprise or something you can’t control, meaning it isn’t a threat.
While this sounds like a bummer (sort of?), there's a way you can totally pull it off if you can create a delay between the time you move to tickle and the time you actually feel it. To do this, you’ll need some outside help from a robot, for example, which can delay your movements.
"Further studies using robots showed that the presence of a small delay between your own movement and the resulting tickle can make the sensation feel tickly," Blakemore told Scientific American. "Indeed, the longer the delay, the more tickly it feels. So it might be possible to tickle yourself if you are willing to invest in a couple of robots!"
In case you were wondering, there are more than a few tickle bots out there, though none seem to work like Blakemore described. For that, you’d need some sort of robotic arm that took in your movement then waited a bit to mimic it.
And there you have it. The reason you can’t tickle yourself is because your brain is actually too active for that happen.
Since tickling is essentially an alert telling you that something is touching sensitive areas of your body - mostly your back, feet, or armpits - your brain doesn’t bother to signal when it knows where the source is coming from.