Scientific American has a "Ask the Expert" series, and someone asked why it was impossible to tickle yourself.
The answer lies at the back of the brain in an area called the cerebellum, which is involved in monitoring movements. 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. 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.Two brain regions are involved in processing how tickling feels. The somatosensory cortex processes touch and the anterior cingulate cortex processes pleasant information. We found that both these regions are less active during self-tickling than they are during tickling performed by someone else, which helps to explains why it doesn't feel tickly and pleasant when you tickle yourself. 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. 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!
Hmm, so the key here seems to be the inability to predict *what* movement someone is going to do to try to tickle you. Only novel sensations tickle, and they aren't novel if you made them. I want to know what study used robots to tickle people. Cause thats just crazy.
Comments
While reading it, I found myself trying to do that and I didn't succeed.
Posted by: BenP | January 31, 2007 12:52 PM
Interesting. I only have to tickle my wife once. Then I can just wiggle my fingers and if she sees it it has the same effect as if I had really tickled her. Makes me think at least part of it is psychsomatic...
Posted by: afarensis | January 31, 2007 1:39 PM
Sarah-Jayne Blakemore (PhD in Coochi Coochi Coo) @ university college london
The paper in Nature Neuroscience, 1998
Awesome :)
Posted by: Cameron | January 31, 2007 7:11 PM
Hmm... I must have some rare neurological condition. I can tickle myself on the feet,without robotic assistance. Should I go see a doctor now?
Posted by: Kim Boone | January 31, 2007 8:49 PM
i can tickle the roof of my mouth and with a little more effort, the bottoms of my feet.
Posted by: knobody | February 1, 2007 1:12 AM
I must be really strange then 'cause I am VERY capable of tickling myself at will. Especially on the knees and ribs. It's never like someone else doing it though...
Posted by: Daniel | February 1, 2007 5:14 AM
w00t! My field!
I see someone already posted the Nature paper, but here are a couple more links to Blakemore's work in which robots are used to tickle people.
Journal of Neuroscience - Predicting the consequences of our own actions: the role of sensorimotor estimation
Neuroreport - Why can't you tickle yourself? (requires subscription)
Posted by: Despard | February 1, 2007 6:25 AM
I can tickle myself also. Why is it such a persistent myth that no-one can ?
Posted by: zzz | February 1, 2007 6:49 AM
Hmmm, maybe the majority of us can't tickle ourselves but a few people can. Does that mean you can't predict your own actions? Quite sneaky! :)
Posted by: Shelley Batts | February 1, 2007 9:23 AM
One biological component of Extraversion is cortical arousal -- it's not that strong of an effect, but it seems to be real. Introverts have higher arousal, and so can't tolerate lots of stimulation (thus preferring to be by themselves), while extraverts are under-aroused and so seek out stimulation by socializing.
I've wondered on my blog before whether introverts are more ticklish -- they react more when you give them electric shocks, squirt lemon juice in their mouths, and so on, so why not be more ticklish? Of those who actually can tickle themselves, I'm guessing being quite introverted plays a role. (I'm incredibly ticklish, can tickle myself somewhat on the ribs and waist, and am definitely a big ol' introvert.)
Posted by: Agnostic | February 1, 2007 11:45 AM
Whether you can tickle yourself or not, the point is that we are less sensitive to self-generated movements then we are to externally imposed sensations.
To those who can tickle themselves: is it as strong a feeling as when other people do it?
Posted by: Despard | February 1, 2007 12:22 PM
The introvert theory sounds reasonable. There are also conditions where the person is particularly sensitive to sensory inputs and overload. Forgotten the name of it now.
Posted by: zzz | February 3, 2007 8:22 AM