More evidence of the human brain's incredible plasticity has come to the fore through a new study of foot painters — professional painters who paint with their feet. Using the feet as hands, the study shows, has led the brain to "see" toes as fingers — almost.
The somatosensory cortex is the region of the brain that receives and processes sensory stimuli from the body, including those of touch.
In this brain region, each finger is mapped separately as an independent entity. In humans, the same is not typically true of toes.
Yet nonhuman primates, which use hands and feet equally for dextrous activities, such as climbing, do have distinct brain areas for each finger and toe.
In a new study, led by researchers from University College London (UCL), in the United Kingdom, the investigators were interested in finding out whether human brains are able to adapt and learn to "view" each toe separately, much like their fingers.
The researchers worked with two foot artists — both males in their 50s — since painting requires dexterity and precision, meaning that individuals who use their feet for such dextrous activities have learned to use them much in the same way that they would use hands. The two professional artists also use their feet to accomplish daily tasks, such as getting dressed and typing.
"For almost all people, each of our fingers is represented by its own little section of the brain, while there's no distinction between brain areas for each of our toes," says lead author Daan Wesselink.
"But in other nonhuman primate species, who regularly use their toes for dextrous tasks like climbing, both the toes and fingers are specifically represented in their brains," he adds.
"Here, we've found that in people who use their toes similarly to how other people use their fingers, their toes were represented in their brains in a way never seen before in people."
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In the study — the findings of which appear in the journal Cell Reports — the researchers worked not just with the two foot painters, but also with 21 individuals who had full use of their hands and who acted as the control group.
First, the team asked all the participants to complete tasks that allowed them to assess toe motor control and sensory perception in the toes.
The researchers noted that, typically, the foot painters would use one foot for highly dextrous activities — such as wielding a paintbrush — and the other to steady themselves. The two also did not wear enclosed footwear most of the time.
This, the investigators inferred, has likely allowed the two artists to develop much more distinctive sensory perception in their toes, rendering the toes more sensitive to stimuli.
At the next stage of the study, the researchers used high resolution functional MRI to scan all the participants' somatosensory cortex areas as they tapped the participants' toes.
The researchers found that in the somatosensory cortex of each foot painter, distinct areas "lit up" for each toe of the dextrous foot as it was being tapped. This looked much like what happens in the brain when different fingers touch something.
Wesselink and colleagues noticed a similar reaction in the brain when they touched the toes of the other foot of each painter, though these areas were less distinctly separated.
As expected, the researchers found no distinct mapping in the somatosensory cortex of any control participant after tapping their toes.
What did surprise the scientists was that the foot artists were no more skillful at wiggling each toe separately than the participants in the control group, despite the fact that they had learned to use their feet for tasks that typically require the use of hands.
However, the artists did have better sensory perception in their toes, compared with the participants in the control group.
One of the painters who agreed to take part in this study, Peter Longstaff, appreciated that the research shed fresh light on just how adaptable the human brain is.
"I've enjoyed helping science by demonstrating how most people's feet are not used to their full potential, and I hope the results will encourage other people to consider unconventional ways to get by without the use of hands," says the artist.
"The body maps we have in our brains are not necessarily fixed — it appears as such because they are very consistent across almost all people, but that's just because most people behave very similarly," co-lead author Harriet Dempsey-Jones, Ph.D., explains.
"Our study demonstrates an extreme example of the brain's natural plasticity, as it can organize itself differently in people with starkly different experiences from the very beginning of their lives," adds the senior author, Tamar Makin, an associate professor of cognitive neuroscience at UCL.