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Why can't we tickle ourselves?


Researchers decipher the phenomenon of ticklishness

Most people are ticklish, but we cannot tickle ourselves. There is also a certain ambivalence in tickling, which is expressed, for example, in the fact that children fight back violently, whom they are tickled, but ask for more as soon as tickling stops. Researchers at the Humboldt University in Berlin have now got to the bottom of the phenomenon and have found an explanation for why you cannot tickle yourself.

As early as 350 BC Chr. Aristotle raised the question why we can not tickle ourselves, reports the research team led by Professor Dr. Michael Brecht from the Humboldt University. In a current study, the researchers used rats to investigate the underlying mechanisms of tickling and they came across surprising connections. They have published their results in the journal "Current Biology".

Tickleness is a mysterious phenomenon

The ticklishness is a mysterious phenomenon on many levels, which has been insufficiently clarified until today. It remained unclear why we cannot tickle ourselves and why “the mere approximation of a tickling hand without touch causes laughter,” explains the research team. The ambivalence between joy and rejection when tickling could not yet be explained. In experiments on rats, the researchers have now tried to find explanations.

Rats can laugh too

Earlier studies had already shown that rats react with a kind of "laugh" in the ultrasound range when tickled by humans, the researchers report. This “laughing” is mediated by the somatosensory cortex, the largest tactile representation in the brain. Tickling by others leads to activation in this region of the brain, which does not occur when you touch yourself. So far, the attempts at explanation here have assumed that this is based on the fact that the brain can distinguish between self-touch and touch by others.

Simple mechanism prevents self-tickling

However, in their current investigations, the researchers concluded that a simpler mechanism is responsible for the fact that we cannot tickle ourselves. Vocalizations, i.e. laughter, as well as the activity of the somatosensory cortex in the rats were suppressed during self-contact (e.g. cleaning). Vocalization and cortex activity, on the other hand, were enhanced when the researchers touched and tickled them.

Oppression in the brain

If the self-touch and the touch of others took place at the same time, the vocalizations and the activity of the somatosensory cortex were also suppressed, the researchers report. This suggests that the rat brain does not differentiate here between self-touch and touch by others. As soon as they pharmacologically blocked the responsible neurons, the sensation of tickling remained even with simultaneous self and external contact.

Ambivalence of tickling

In further experiments, the researchers taught the rats how to request a tickle interaction, and although the rats did so voluntarily, they sometimes "prematurely discontinued this tickling initiation and showed escape behavior, rigidity, and vocalizations usually associated with negative emotions. “A puzzling ambivalence comparable to the behavior of children described above. The researchers were also able to decipher why tickling can work before it has been touched. A deep-lying layer of the somatosensory cortex was activated during self-initiation even before the tickle interaction began.

"Inhibitory brake" when touching yourself

According to the researchers, the study results suggest that when you touch yourself, an "inhibitory brake" is activated in the somatosensory cortex so that we cannot tickle ourselves. The ambivalence regarding tickling is apparently also a behavioral reaction that is shared by rats and humans. And last but not least, the study showed that activation occurs in the somatosensory cortex not only when touched, but also when you expect to be tickled. (fp)

Author and source information

This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Dipl. Geogr. Fabian Peters

Swell:

  • Shimpei Ishiyama, Lena V. Kaufmann, Michael Brecht: Behavioral and Cortical Correlates of Self-Suppression, Anticipation, and Ambivalence in Rat Tickling; in: Current Biology (published 09/26/2019), cell.com/
  • Humoldt University of Berlin: Why can't we tickle ourselves? (published September 26, 2019), hu-berlin.de


Video: Why We Cant Tickle Ourselves (January 2022).