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.
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.
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.
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 BŲhme, who is a postdoctoral fellow in the Department of Clinical and Experimental Medicine and the Center for Social and Affective Neuroscience (CSAN), LinkŲping University, Sweden.
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 BŲhme.
The research was funded by ALF grants from Region ÷stergŲtland. 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)