How our brain interprets touch

Foreign contact is processed differently than self-contact

How does our brain process touch? © Thor Balkhed / Linköping University
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Do we touch ourselves or do we touch each other? For our brains this makes a big difference. As experiments show, our mind reacts to foreign contact with the activation of numerous areas of the brain. When we touch ourselves, the activity of many brain regions is downregulated. The insights into these neural processes explain the phenomenon of tickling, but could also advance the study of diseases such as schizophrenia.

A casual stripe on the arm, a firm handshake or an intimate embrace: touches are naturally part of our everyday life. However, touch is not the same as touching. How we perceive stimulation of our skin depends on the type of contact. On the other hand, it also matters who touches us.

So we respond to the touch of a familiar person other than a stranger's. Touching yourself feels completely different than touching another person's skin. This distinction between foreign and personal touch is very important to our body sense - and it explains why most people can not tickle themselves.

Test persons in the petting test

But what actually happens in our brain? This has now been investigated by Rebecca Böhme from Linköping University in Sweden and her colleagues. To find out how the distinction between foreign and self-contact on the neuronal level shows, they invited volunteers to the petting test.

For the experiment, the participants should either caress themselves slowly over the arm or they were touched in the same way by another person. The scientists used functional magnetic resonance imaging (fMRI) to observe what was happening in the subjects' brains. The result: "We saw clear differences between being touched and self-touching, " reports B hme. display

Brain areas that are deactivated when self-touching. Rebecca Böhme

Deactivation by self-contact

For example, another person's touch activates a number of brain regions, including the somatosensory cortex, the islet cortex, the amygdala, the cerebellum, and the prefrontal cortex. If the participants were themselves, many brain areas were deactivated.

Interestingly, the researchers found evidence that these striking differences do not show up in the brain - but already one step ahead. "The distinction already seems to take place in the spinal cord before the touch stimuli are transmitted to the brain and processed there, " explains Böhme.

New Findings on Schizophrenia and Co?

According to the scientists, these results fit with a theory that the brain can partly predict the sensory consequences of our actions. Thus, it does not pay much attention to stimuli caused by our own body, because it already expects the information that comes from it.

The de fi nition of the neural basis of this distinction could now also help in the study of diseases such as autism or schizophrenia, as B hme and her colleagues emphasize. For these diseases appear to be partly based on disorders of somatosensory processing.

Some schizophrenia patients, for example, may be tickling themselves, unlike most people. This suggests that her brain interprets sensory stimuli triggered by her own body differently. (Proceedings of the National Academy of Sciences, 2019; doi: 10.1073 / pnas.1816278116)

Source: Link ping University / PNAS

- Daniel Albat