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Most people cannot tickle themselves – their own touch does not cause any sensations. But in patients with schizophrenia, everything is different: the fact is that they do not distinguish between their own and other people’s touches.
It is believed that our brain (more precisely, the somatosensory cortex) predicts in advance the tactile sensations from our own actions (even if we touch ourselves not with our fingers, but with some object like a feather or brush) and therefore they do not provoke such a reaction, because they are not considered important. However, back in 2000, neuroscientist Sarah-Jayne Blakemore and her colleagues demonstrated that some patients with schizophrenia can tickle themselves (only those who had symptoms such as auditory hallucinations and the feeling that their thoughts and actions are controlled from the outside). The researchers hypothesized that these patients have little or no ability to distinguish between their own touches and those of others.
There are mental disorders similar to schizophrenia in causes and symptoms, but less severe (eg, schizotypal personality disorder). A group of French researchers from the University of Lille decided to find out if people with pronounced schizotypal traits can tickle themselves.
To begin with, the researchers tested 397 students with no psychiatric diagnoses using a questionnaire to identify schizotypal traits (in which, in particular, it turned out that the respondent had unusual beliefs, beliefs, experiences and sensations, as well as the feeling that his thoughts and actions externally controlled) and selected 27 students with the lowest and highest scores for participation in the experiment.
Pass the tests
- Can you laugh at yourself?
In the course of the experiment itself, blindfolded students first tickled their own hand with an ordinary brush, then with the same brush their hand was tickled by a special device. Participants were asked to rate how intense the tickling sensation was on each occasion.
In the case where the brush was moved by a robotic hand, students with and without schizotypal personality traits were approximately equally ticklish. However, participants with schizotypal traits were significantly more ticklish than others when they themselves held the brush (students without schizotypal traits in this case were not or almost not tickled).
As the researchers emphasize, these results do not mean that any person who is tickled by their own touch is at an increased risk of developing schizophrenia. However, they allow us to understand more about the mechanisms that are common to all disorders of the schizophrenia spectrum and lead to the fact that the brain does not distinguish well or does not distinguish between its own and other people’s actions.
Подробнее см. А. Lemaitre et al. «Individuals with pronounced schizotypal traits are particularly successful in tickling themselves», Consciousness and Cognition, vol. 41, April 2016.