Cell uncovers the mystery of touch: why certain body parts are so sensitive

Researchers have discovered a mechanism that can explain why certain body parts are so sensitive
.

Certain parts of the body—such as our hands and lips—are more sensitive than others, making them an important tool in our ability to discern the most intricate details of the world around us
.

This ability is the key to our survival, allowing us to safely navigate the surrounding environment and quickly understand and respond to new situations
.

The brain provides a considerable amount of space for these sensitive skin surfaces.

But how does the connection between sensory neurons and the brain produce such sensitive skin?

A new study led by researchers at Harvard Medical School has revealed a mechanism that may be the reason why certain skin areas are more sensitive
.

The study was conducted on mice and was published in the journal Cell on October 11
.

Studies have shown that the over-representation of the sensitive skin surface in the brain is formed in early puberty and can be determined to be the brainstem

David Ginty, professor of neurobiology at Harvard Medical School and senior author, said: "This study provides a mechanistic understanding of why there are more brain areas on the surface of the skin with high tactile sensitivity
.

" "Basically, this is one thing .

Although this study was carried out in mice, the overdistribution of sensitive skin areas in the brain can be seen in all mammals-suggesting that this mechanism may also be applicable to other species
.

From an evolutionary perspective, mammals have very different body shapes, which means different skin surface sensitivities

In addition, although these findings are fundamental, they may one day help clarify touch abnormalities that occur in certain neurodevelopmental disorders in humans
.

Scientists have known for a long time that certain body parts occupy too many positions in the brain.
As described by the sensory map of the brain, this picture is the famous "body-sensory homunculus" (body-sensory homunculus), which depicts A schematic diagram of various parts of the human body and the corresponding areas in the brain that process signals from these body parts
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This eye-catching illustration includes cartoon-like oversized hands and lips

"We noticed that the number of neurons innervating sensitive skin is quite small compared to what we expected," said neurobiology researcher and co-first author Brendan Lehnert
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He co-led the research with Celine Santiago, also a researcher in Ginty's lab

"This is unreasonable," Ginty added
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To study this contradiction, the researchers conducted a series of experiments on mice, imaging the brain and neurons when they were stimulated in different ways
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First, they studied how different skin areas in the brain appear throughout the development process

Ginty said: "This immediately tells us that in addition to the innervation density of skin nerve cells, there are other reasons that lead to the overexpression of the brain
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"

Lehnert added: "It's really unexpected to see changes at these developmental time points after birth
.

" "This may be just one of many important changes in postpartum development.
These changes allow us to represent the sense of touch around us.
The world helps us gain the ability to manipulate objects in the world through sensorimotor circuits, and touch is a special part of it
.
"

Next, the research team determined that the brainstem (the area at the bottom of the brain responsible for transmitting information from sensory neurons to the more complex, higher-order brain areas) is where the magnified representation of the sensitive skin surface appears
.
This discovery made the researchers realize that the overrepresentation of sensitive skin must come from the connection between sensory neurons and brainstem neurons
.

For further research, the scientists compared the connections between sensory neurons and brainstem neurons in different types of paw skin
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They found that the connections between sensitive, hairless skin neurons were stronger and more numerous than that of less sensitive, hairy skin
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Therefore, the research team concluded that the strength and number of connections between neurons play a key role in the overexpression of sensitive skin in the brain
.
Finally, even if the sensory neurons on the sensitive skin were not stimulated, the performance in the mouse brain was still expanding-this suggests that the skin type, rather than the long-term touch stimulation, caused these brain changes
.

Ginty said: "We think we have discovered a component of this magnification that explains the disproportionate central representation of sensory space
.
This is a new way of thinking about how this magnification occurs
.
"

Next, the researchers want to study how different skin areas make the neurons that stimulate them have different characteristics.
For example, when they stimulate sensitive skin, they form more and stronger connections
.
"What signal?" Ginty asked
.
"This is a very important mechanical issue
.
"

Although Lehnert described the pure curiosity of the study, he pointed out that there is a link between the effects of human neurodevelopmental disorders called developmental coordination disorder and contact receptors and the brain, so it may help to further clarify the relationship between the two.
Interaction
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Lehnert said: "This is one of the many studies I hope that these studies will explore the changes in the body's performance during development on a mechanical level.

Both Celine and I believe that at some point in the future, this may allow us Better understand certain neurodevelopmental disorders
.
"

Article retrieval:

Mechanoreceptor synapses in the brainstem shape the central representation of touch

Reference: 11 October 2021, Cell .

DOI: 10.
1016/j.
cell.
2021.
09.
023