Why after 2000 years we still don't know how tickling works

Socrates wondered 2,000 years ago, and Charles Darwin also racked his brains: what is a tickle, and why are we so sensitive to tickling? 'Tickling is relatively under-researched,' says neuroscientist Konstantina Kilteni. She argues that tickling is a very interesting subject for research. 'It is a complex interplay of motor, social, neurological, developmental and evolutionary aspects. If we know how tickling works at the brain level, it could provide a lot of insight into other topics in neuroscience. Tickling can strengthen the bond between parents and children, for instance, and we usually tickle our babies and children. But how does the brain process ticklish stimuli and what is the relationship with the development of the nervous system? By investigating this, you can learn more about brain development in children.'

Research also shows that people with autism spectrum disorder, for example, perceive touches as more ticklish than people without autism spectrum disorder. Investigating this difference could provide insight into differences in the brains of people with autism spectrum disorder and people without and could help with getting knowledge about autism.

'But we also know that apes such as bonobos and gorillas respond to ticklish touches, and even rats have been observed being so. From an evolutionary perspective, what is the purpose of tickling? What do we get out of it?'

The fact that you cannot tickle yourself is also interesting from a scientific point of view: 'Apparently, our brain distinguishes ourselves from others, and because we know when and where we are going to tickle ourselves, the brain can switch off the tickling reflex in advance. But we don't know what exactly happens in our brain when we are tickled.'

Tickling or tickling

Kilteni argues that these questions have not yet been answered because it has not been clearly defined what tickling actually is within the scientific community -- there is a difference between when you tickle someone hard someone on the armpits, for instance, with your hands and tickling someone's back lightly with a feather. The first sensation is understudied while we know much more for the second feather-like stimulation. It is also difficult to compare between existing studies: when someone is tickled by another person, it is difficult to replicate that form of tickling exactly with another test subject.

Tickling lab

Kilteni has a tickling lab for this very purpose: it contains a chair with a plate with two holes in it. You put your feet through the holes and then a mechanical stick tickles your footsoles. That way, every tickle experiment is the same. The neuroscientist records exactly what happens in your brain and also immediately checks all other physical reactions, such as heart rate, sweating, breathing, or laughter and screaming reactions. 'By incorporating this method of tickling into a proper experiment, we can take tickling research seriously. Not only will we be able to truly understand tickling, but also our brains.'