The stroke of a feather brushing up against our feet, stomach, or even our neck can elicit a boisterous laugh even from the most serious of people. The unexpected sensation makes us sensitive to this touch, but do we have the ability to shiver and giggle and tickle ourselves? According to a recent study, people with schizophrenic-like traits may be able to tickle themselves.

A team of researchers in France, led by Anne-Laure Lemaitre, analyzed a total of 397 healthy students including 27 students who scored highly on the Schizotypal Personality questionnaire, and 27 students who scored very low. The questionnaire included questions on unusual beliefs and strange perceptual experiences. Students also completed a questionnaire about whether they ever felt passive, or “a robot or zombie without a will of your own."

The two groups took part in different tickle tasks involving a brush. The students either tried to self-tickle their forearm with the brush, or had the researcher tickle them with it. Afterward, they rated how ticklish the brush movements felt on their arm.

The findings published in the journal Consciousness and Cognition revealed those who scored high in schizotypal traits were no more ticklish in general than the low schizotypal students. However, the highly schizotypal students found the self-tickling experiment more ticklish than their counterparts. Moreover, they also found the self-tickling experiment was just as ticklish as when the researcher did the tickling, unlike the low schizotypal students.

Most of us are unable to tickle ourselves because the brain categorizes self-produced movements as less significant than those initiated by others. However, previous research shows people with schizophrenia have the ability to tickle themselves, and suspect it's due to the neurological changes in the brain that disable their ability to differentiate self-initiated actions. In other words, they are able to process the intent to move, and are aware the movement has occurred. However, they cannot link the sensation — the tickle — to the fact they’re responsible for making the movement.

Although we can't tickle ourselves, this puts us at an advantage; fMRI scans show we're not able to tickle ourselves because the primary somatosensory cortex and secondary somatosensory cortex — areas that receive sensory information from thalamic nerve projections — indicate that the brain appears to be able to predict what the sensation will be. The ability to visualize possible outcomes may boost our response time to potentially dangerous stimuli and help us distinguish between real external threats, such as a poisonous snake near us, and those we create ourselves, like resting our head in our hands.

The current study gives psychologists insight on the possible brain mechanisms that contribute to schizophrenics' hallucinations. If they’re unable to discern between external and internal sensations during tickling, they may also convince themselves that they’re actually hearing someone else’s voice when they’re actually mumbling to themselves.

As for the rest of us, if we can tickle ourselves, this doesn’t mean we’re more likely to be schizophrenic. Rather, it supports the idea that the same brain processes (involved in movement control and monitoring) that possibly contribute to symptoms experienced by schizophrenics, could also contribute to schizophrenia-like traits.

So, go ahead and tickle yourself and have a good laugh.

Source: Lemaitre AL, Luyat M, Lafargue G. Individuals with pronounced schizotypal traits are particularly successful in tickling themselves. Consciousness and Cognition. 2016.