Artists who paint with their feet have 'toe maps' in their brains that can be used to develop advanced prosthetic limbs
Researchers studied two foot artists, born without arms, to examine if a lifetime of highly-changed experiences can cause new body maps in the brain
Artists who paint with their feet have finely tuned "toe maps" in their brains where each toe can be linked to an area of brain activity. Humans have well-defined hand maps, but this is the first time that similarly robust toe maps have been identified in people, shows a new study.
The findings can help in making advancements in the field of prosthetics or artificial limbs, says a research team from the brain plasticity laboratory led by Dr. Tamar Makin at the Institute of Cognitive Neuroscience, University College London.
The researchers used a technique called functional magnetic resonance imaging or functional MRI (fMRI) that measures brain activity by detecting changes in the blood flow.
According to them, mapping out finger and toe activity in the brain can help advance brain-machine interface technology where the brain learns how to control "each digit (toe)" of a prosthetic. The team adds that the findings also raise questions about how the limbs we use every day are represented in the brain.
"We investigated two foot artists, born without arms, asking if a lifetime of radically altered bodily experience can cause new body maps in the brain. We provided evidence that complex toe behavior supports organized 'hand-like' activity in the artists' foot and (missing) hand areas, significantly more so than in controls," say researchers in their findings, published in the journal Cell Reports.
The research team regularly worked with a network of amputee or congenital limbless support groups, limbless musicians, and participants in the Cybathlon (the world's Olympics for robotic prosthetics) to study how the brain adapts to limblessness or changes in limb function.
While the group usually focuses on the hand, the current work focused on two foot artists who paint with their feet as they were born without arms, to learn more about the mysteries of human toe maps.
The artists — Tom Yendell and Peter Longstaff — are two of only three foot artists in the UK. They were born without upper limbs and have developed "extreme dexterity" with their feet because they use them to perform most daily activities, says the team.
"Displaying exquisite compensatory adaptation, these individuals perform typically manual daily living tasks (for example, dressing, feeding, and typing) with their feet. Both use one foot for dextrous object manipulation and the other for stabilizing. Both are sufficiently skilled with their dextrous foot to allow writing, drawing, and painting to a level that supports their profession as artists," state the findings.
Within the brain area (somatosensory cortex), each part of the body is laid out in an organization that roughly approximates what it looks like in the actual human body to form a body map. The researchers knew that people with hands do not have toe maps, but non-human primates do.
To better understand why humans appear to lack this brain organization, the research team conducted a series of fMRI studies on Yendell and Longstaff as well as on nine male volunteers who had upper limbs.
While the "limbed" volunteers were in an fMRI machine, the researchers touched one finger or toe at a time to see what area of the brain was activated. As expected, researchers found that the fingers of the hand show individual spots of activity right next to each other.
However, when researchers examined the toes of handed individuals via fMRI using the same methods, they did not show identifiable toe maps. According to researchers, it turns out that even though humans have individual digits (toes) on their feet, when "we touch each toe in order, we do not see a nice organized pattern".
"The artists, in contrast, both have individualized areas for each of the toes next to each other as they are in the body, that is, they have toe maps. The maps in the artists are in the same area of the brain and oriented in the same direction as those in non-human primates," says the study.
The findings throw open many unanswered questions about brain plasticity and why these individuals with extreme toe agility have toe maps, while others do not. The team points to two different possibilities.
They say it could be possible that all primates are born with organized toe maps, but they are lost in humans because we do not use our toes or because feet are usually enclosed in shoes.
The other possibility, says the team, could be that humans are born without toe maps but develop them if they use their bodies in "particularly dexterous" ways, as in the case of the artists.
According to study co-author Daan Wesselink, there is a critical period of plasticity early in life when the brain seems particularly capable of change. "It could be that our artists were learning to use their toes when they were children during this time of maximal brain plasticity, points out Wesselink.
The co-author adds: "We know the adult brain is more fixed once the critical period of plasticity closes. It may be that once that happens, you cannot really change the brain in a major way, such as this."
Researchers further say that since the artists were born without hands, they probably have a very different brain plasticity history when they were growing up. "There could be some aspects related to brain changes that dramatically shift because they are born without upper limbs and hands," says Wesselink.
They will now use their findings to see if they can incorporate "different non-body-like technology", such as a robotic prosthesis, into an adult individual's body map.
"Whether it is the hand or toe, or any body part, we want to understand more about how the brain copes with these different types of changes," says the first author of the study Dempsey-Jones.