How Does the Brain Differentiates Between Self and Other's Touch?

Brain is capable of distinguishing between self-touch and touch by another person. This occurs due to the brain’s ability to reduce the sensory perception in the case of self-touch, compared to non-self touch.

Highlights:

Brain can distinguish between touch by one’s self and touch by another person
This occurs due to the brain’s ability to downregulate the sensory stimuli arising from self-touching, as opposed to touching by another person
This helps to understand how the brain differentiates touch sensations arising from self-touch and non-self touch

Our brain reduces the sensory perception of touch from an area of skin touched by ourselves, reveals a new study carried out by researchers at Linköping University, Sweden. The study findings increase our understanding of how the brain differentiates between self-touch and touch by another person.

The ability to distinguish between ‘self’ and ‘non-self’ is very important. This distinction first manifests in newborn babies in the early years of life, when they are touched by their caregivers.

Problems associated with self-concept become evident in various types of psychiatric disorders. For example, although normal persons usually can’t tickle themselves, schizophrenia patients can. This is because their brains interpret sensory information originating from self-touch differently to normal people.

The study has been published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS), which is the official scientific journal of the US National Academy of Sciences, published since 1915.

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‘The brain is capable of distinguishing between touch by one’s self and touch by another person. This is possible due to the brain’s ability to reduce the sensory perception in case of self-touching, compared to touching by another person.’
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Sensory Receptors of the Skin

The epidermis and dermis have sensory receptors that can sense various types of stimuli, including the following:

Mechanoreceptors: Touch (pressure, vibration, and texture)
Nociceptors: Pain
Thermoreceptors: Temperature (hot and cold)

The information about touch is relayed from the mechanoreceptors in the skin to the brain via the spinal cord. The brain interprets this information to perceive the sensation of touch.

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Study Technique

The research team studied the sensation felt in different parts of the nervous system by touching the skin of the study participants by another person and compared this with self-touching at the same places on the body.

The study participants were made to lie down on a moveable platform that could enter into a magnetic resonance imaging (MRI) machine. The participants were asked to slowly stroke their arm with their own hand, which was followed by similar stroking by another person.

Simultaneously, brain imaging was carried out by functional MRI (fMRI) to generate images corresponding to the brain activity in real-time. This helped the researchers to understand how these types of touch affected the activity in various regions of the brain.

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Study Findings

The research team found that in the case of self-touch, the brain modulated the processing of the sensory perception in such a way that it was appreciably reduced, compared to touch by another person.

For example, in one experiment, the study participants were stroked on their arm with filaments of different thickness, while simultaneously being stroked by themselves or by another person. The research team found that when two sensory stimuli were simultaneously applied, the sensation of touch was significantly ‘dampened’ by the brain when the participants stroked their own arm.

“We saw a very clear difference between being touched by someone else and self-touch. In the latter case, activity in several parts of the brain was reduced. We can see evidence that this difference arises as early as in the spinal cord, before the perceptions are processed in the brain”, says first author Dr. Rebecca Böhme, who is a postdoctoral fellow in the Department of Clinical and Experimental Medicine and the Center for Social and Affective Neuroscience (CSAN), Linköping University, Sweden.

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Interpretation of the Findings

The study findings could be interpreted in the light of a theory on brain research that highlights the fact that the human brain does not attach as much importance to sensations generated by our own bodies, such as touching one’s self, as compared to touching by another person.

“Our results suggest that there is a difference as early as in the spinal cord in the processing of sensory perceptions from self-touch and those from touch by another person. This is extremely interesting. In the case of the visual system, research has shown that processing of visual impressions occurs as early as in the retina, and it would be interesting to look in more detail into how the brain modulates the processing of tactile perceptions at the level of the spinal cord”, says Rebecca Böhme.

Funding Source

The research was funded by ALF grants from Region Östergötland.

Reference:

Distinction of Self-produced Touch and Social Touch at Cortical and Spinal Cord Levels - (https://www.pnas.org/content/early/2019/01/14/1816278116)

Source-Medindia