Introducing the brain: how fine-touch areas work (Introduction)

by David Turell , Monday, October 11, 2021, 19:03 (1137 days ago) @ David Turell

Very sensitive skin regions have many extra brain connections:

https://medicalxpress.com/news/2021-10-unraveling-mystery-mechanism-uncovered-body.html

"Some parts of the body—hands and lips, for example—are more sensitive than others, making them essential tools in our ability to discern the most intricate details of the world around us.

"This ability is key to our survival, enabling us to safely navigate our surroundings and quickly understand and respond to new situations. It is perhaps unsurprising that the brain devotes considerable space to these sensitive skin surfaces that are specialized for fine, discriminative touch and continually gather detailed information via the sensory neurons that innervate them.

"But how does the connection between sensory neurons and the brain result in such exquisitely sensitive skin?

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"The research, conducted in mice and published Oct. 11 in Cell, shows that the overrepresentation of sensitive skin surfaces in the brain develops in early adolescence and can be pinpointed to the brain stem. Moreover, the sensory neurons that populate the more sensitive parts of the skin and relay information to the brain stem form more connections and stronger ones than neurons in less sensitive parts of the body.

"'This study provides a mechanistic understanding of why more brain real estate is devoted to surfaces of the skin with high touch acuity,"

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"While the study was done in mice, the overrepresentation of sensitive skin regions in the brain is seen across mammals—suggesting that the mechanism may be generalizable to other species. From an evolutionary perspective, mammals have dramatically varied body forms, which translates into sensitivity in different skin surfaces. For example, humans have highly sensitive hands and lips, while pigs explore the world using highly sensitive snouts. Thus, Ginty thinks this mechanism could provide the developmental flexibility for different species to develop sensitivity in different areas.

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"Scientists have long known that certain body parts are overrepresented in the brain—as depicted by the brain's sensory map, called the somatosensory homunculus, a schematic of human body parts and the corresponding areas in the brain where signals from these body parts are processed. The striking illustration includes cartoonishly oversized hands and lips. Previously, it was thought that the overrepresentation of sensitive skin regions in the brain could be attributed to a higher density of neurons innervating those skin areas. However, earlier work by the Ginty lab revealed that while sensitive skin does contain more neurons, these extra neurons are not sufficient to account for the additional brain space.

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"To probe even further, the scientists compared the connections between sensory neurons and brain stem neurons for different types of paw skin. They found that these connections between neurons were stronger and more numerous for sensitive, hairless skin than for less sensitive, hairy skin. Thus, the team concluded, the strength and number of connections between neurons play a key role in driving overrepresentation of sensitive skin in the brain. Finally, even when sensory neurons in sensitive skin weren't stimulated, mice still developed expanded representation in the brain—suggesting that skin type, rather than stimulation by touch over time, causes these brain changes.

"'We think we've uncovered a component of this magnification that accounts for the disproportionate central representation of sensory space." Ginty said. "This is a new way of thinking about how this magnification comes about.'"

Comment: this pattern requirews design to fit the touch needs. Not by chance.