How the Brain Relies on Sight in the Absence of Touch

Article: ...The human brain may tap into visual cues when lacking a sense of touch
Source: University of Chicago Medicine
Published: February 26, 2021
Article: Human brain taps into visual cues when lacking a sense of touch
Source: University of Birmingham (U.K.)
Published: February 18, 2021
Article: ...The brain compensates through visual cues when lacking sense of touch
Source: Bournemouth University (U.K.)
Published: February 16, 2021

Somatosensation, the combined sense of touch and proprioception, is integral to how we navigate our body in space. We are aware of our embodiment even when we close our eyes. But what happens when we lack this sensory experience from our body, and how does our brain adapt? How do other senses, notably sight, compensate to generate a sense of the body? Researchers recently had that opportunity to study two unique individuals without somatosensation, one case acquired, the other congenital. Ian from the U.K. developed a complete loss of his sense of touch and proprioception (the awareness of our body's position and movement) below the neck at age 19 after what is believed to be an autoimmune response after illness; Ian required months of rehabilitation to learn to move his body and limbs again. Kim from the U.S., on the other hand, was born without sensory nerve fibers to feel her body, consequently possessing neither touch sensation nor proprioception.

Kim's hand maps (top) and Ian's hand maps (bottom)

For the study, Ian and Kim, along with age-matched controls, participated in experiments designed to assess their mental image of their bodies and their unconscious sense of their bodies in space. The researchers found that Kim's representation of her hand was closer to that of the controls in that both were distorted; for the controls, this is due to a distorted sensory map. Ian, by contrast, had a more accurate representation of his hand compared to Kim and the controls. The investigators hypothesize that the greater accuracy is because Ian's hands are always under his conscious control. In an experiment related to body schema, the researchers looked at how the participants reacted when a visual target appeared near their hand, i.e., within their peri-personal space. Those with intact proprioception would react rapidly. They found that Kim's results closely matched the controls compared to Ian's, suggesting that Kim has an unconscious representation of her body despite never having been able to feel it. This is similar to the way a person will instinctively duck when a ball flies toward them, even before consciously processing what the object is. Ian, however, relies on much slower processes involving conscious visual perception. The differences between Ian's and Kim's conditions highlight how conscious compensatory mechanisms developed in adulthood after sensory loss differ from the neuronal reorganization that might occur in a person born without that sense. However, whether unconsciously or consciously, we all arrive at a sense of self. As one of the researchers concludes, "What we can learn from this is that you might not do it in the way that others do it, but you will find a way to make a body schema. You will find a way to make a sense of yourself."

My rating of this study: ⭐⭐🌸

Miall RC, Afanasyeva D, Cole JD, et al. "Perception of body shape and size without touch or proprioception: evidence from individuals with congenital and acquired neuropathy." Experimental Brain Research.  239:1203–1221. 12 February 2021. https://doi.org/10.1007/s00221-021-06037-4