Something rather unfortunate has happened to me recently. My boyfriend discovered I am extremely ticklish. He’s stronger than me (damn you sexual selection!!) and can hold me down so there’s nothing I can do. I can’t even express my irritation because I can’t stop laughing!
Now, don’t worry, I’m not super into sharing the details of my relationship online and calling it science– but I thought I’d tell you this story as it gave me the idea for this blog post. After he got bored of torturing me, we spent the next hour discussing how tickling works (don’t judge, it’s just what scientists do). What makes you laugh and jerk uncontrollably when you’re being tickled, and why? So as the ever-inquisitive scientist, I researched it, and here is what I found…
How does tickling work?
When the nerve endings just under your skin are lightly stimulated, this information gets sent back through your nervous system to your brain. Scientists have used MRIs to identify the two areas of the brain where this information gets processed. Firstly, the somatosensory cortex which is responsible for analysing touch, and secondly, the anterior cingulated cortex, which deals with pleasant feelings. Together, the stimulation two areas create the feeling we would identify as ‘tickling’.
Why do we laugh?
Originally it was thought that we laughed when being tickled because we found it funny. But in fact, laughing while being tickled and humour are not actually connected (see boyfriend, I don’t think it’s funny!). Instead, laughing is an involuntary response to the tickling sensation. Evolutionary biologists theorise that tickling may be the most reliable and ancient stimulus of laughter. Neuroscientist Robert R. Provine believes tickling is a mechanism for social bonding between close companions such as family members, friends and lovers. Tickling seems to be a form of play fighting in social groups, with the laughter keeping the ‘fight’ benign and reinforcing social relationships.
Can you tickle yourself?
Try it… it won’t work. This is because our brain is not very good at keeping secrets from itself. The cerebellum, which is responsible for governing movement, can predict a self-tickle and alerts the rest of the brain that it’s coming. As a result, the intensity of the sensation is muted, because the brain does not see the stimulation by its own hand to be of much notice. This is called sensory attenuation, and it supports the theory that tickling evolved as a social behaviour to strengthen social bonds.
Check out Provine’s paper “Laughing, Tickling, and the Evolution of Speech and Self” for a more detailed look into the evolution of laughter and tickling.
Plus, you should listen to the podcast of The Science Hour where guest presenter Liz Barber discussed the science of laughter (and yes, I may have also been a guest on that particular show, but lets pretend this is not shameless self cross-promotion).