Tom Yendell creates stunningly colorful landscapes of purple, yellow and white flowers that jump out of the canvas. But unlike most artists, Yendell was born without arms, so he paints with his feet. For Yendell, painting with toes is the norm, but for neuroscientists, the artistic hobby presents an opportunity to understand how the brain can adapt to different physical experiences.
“It was through meeting and observing [Yendell] doing his amazing painting that we were really inspired to think about what that would do to the brain,” says Harriet Dempsey-Jones, a postdoctoral researcher at the University College London (UCL) Plasticity Lab. The lab, run by UCL neurologist Tamar Makin, is devoted to studying the sensory maps of the brain.
Sensory maps assign brain space to process motion and register sensations from different parts of the body. These maps can be thought of as a projection of the body onto the brain. For example, the area dedicated to the arms is next to the area dedicated to the shoulders and so on throughout the body.
Specifically, Makin’s team at the Plasticity Lab studies the sensory maps that represent the hands and the feet. In handed people, the brain region dedicated to the hands has discrete areas for each of the fingers, but unlike these defined finger areas, individual toes lack corresponding distinctive areas in the brain, and the sensory map for feet looks a bit like a blob. Dempsey-Jones and colleagues wondered whether the sensory maps of ‘foot artists’ like Yendell would differ from those of handed people.
Dempsey-Jones invited Yendell and another foot artist named Peter Longstaff, both part of the Mouth and Foot Painting Artists (MFPA) partnership, into the lab. The scientists interviewed the two artists to assess their ability to use tools designed for hands with their feet. To Dempsey-Jones’ surprise, Yendell and Longstaff reported using most of the tools they were asked about, including nail polish and syringes. “We were just continuously being surprised at the level of ability they had,” Dempsey-Jones says.
Then the researchers used an imaging technique called functional magnetic resonance imaging, or fMRI, to develop a picture of the sensory maps in Yendell and Longstaff’s brains. The researchers stimulated the artists’ toes by touching them one at a time to see which specific parts of the brain responded to the stimuli. As they stimulated each toe, distinct areas lit up. They found highly defined areas in the brain dedicated to each of the five toes, one next to the other. In the control group of handed people, these toe maps did not exist.
For Yendell, who had been part of brain imaging studies before, the defined toe maps didn’t come as a surprise. “I'm sure if you take a table tennis player who has a very different way of using their hand, the brain map will be slightly different to the average person. I think there's lots of instances where it wouldn't be out of the ordinary to be different in any way.”
Scientists have known for a long time that the brain is malleable. With training and experience, the fine details of sensory maps can change. Maps can be fine-tuned and even reshaped. However, scientists had never observed new maps appearing in the brain. Dan Feldman, a professor of neurobiology at the University of California, Berkeley, who was not part of the study, believes the findings are a striking demonstration of the brain’s capacity to adapt. “It builds on a long history of what we know about experience-dependent changes in sensory maps in the cortex,” he says. “[The research] shows that these changes are very powerful in people and can optimize the representation of the sensory world in the cortex quite powerfully to match the experience of the individual person.”
The research has important implications for the newly emerging technology of brain-computer interfaces (BCIs). BCIs are devices that can translate brain activity into electrical commands that control computers. The technology is intended to improve the lives of people without limbs and people recovering from a stroke. Understanding the fine details of how the body is represented in the brain is critical for more accurate development of brain-computer technologies.
“If you want to have a robotic limb that moves individual digits, it's very useful to be able to know that you have individual digits represented, specifically in the brain,” Dempsey-Jones says. “I think the fact that we can see such robust plasticity in the human brain argues that we can maybe gain access to these changeable representations in a way that might be useful for restoring sensation or for a brain-machine interface,” Feldman adds.
But a fundamental question remains: How do these toe maps arise? Are they present at birth and maintained only if you use your toes frequently? Or are they new maps that arise in response to extreme sensory experiences? Dempsey-Jones believes, as with most processes in biology, the answer is a little bit of both. She says there is probably a genetic predisposition for an organized map, but that you also need sensory input at a particular time of life to support and fine-tune it.
Yendell recalls scribbling and even winning a handwriting competition when he was two or three years old. The Plasticity Lab wants to understand how these early events drive the establishment of toe maps. By looking at early childhood experiences, Dempsey-Jones and her team might be able to identify which timepoints are necessary for the development of new sensory maps in the brain. “We've found that if limb loss occurs early enough, you have brain organization similar to someone born without a limb,” she says.
Once scientists determine the periods of development that generate this unique organization of toe maps, the improved understanding of the brain could lead to better technologies for people who are disabled or missing limbs. Yendell, who is on the board of the MFPA, is more than happy to contribute to these types of studies. “Anything that helps other people understand and overcome things, then you've got to do it.”
This piece was produced in partnership with the NPR Scicommers network.