Scientists have long known that humans have unique neural “hand maps,” or regions of the brain tasked with processing sensations experienced by each of the five fingers. These patterns vary depending on individuals’ everyday activities. A pianist’s hand map, for example, might differ from that of a surgeon, a rock climber or a writer, as each of these occupations involves a unique set of regular movements.
But new research suggests the brain’s mapping abilities are even more extensive than previously believed. As researchers led by Harriet Dempsey-Jones and Daan B. Wesselink of University College London report in the journal Cell Reports, two professional foot painters assessed using high-resolution brain imaging possess “toe maps” that appear to be just as effective as more typical hand maps.
According to Francie Diep of the New York Times, most humans’ neural foot maps do not differentiate between individual toes. Compared with hand maps, which constitute distinct clusters associated with separate fingers, an average foot map manifests in the brain as a solid region.
This isn’t the case for Tom Yendell and Peter Longstaff, both of whom were born without arms after their mothers took a pregnancy drug later proven to cause birth defects. Instead of exhibiting solid foot maps, both men boast complex neural networks in which specific regions of the brain correspond with each individual digit. Previously, Laura Sanders explains for Science News, this kind of toe mapping has only been observed in the brains of nonhuman primates, which regularly use their feet for tasks such as climbing.
“We’re talking here about a whole map that doesn’t usually exist in adults,” Ella Striem-Amit, a neuroscientist at Georgetown University who was not involved in the study, tells the Times.
Writing for the Conversation, Dempsey-Jones notes that Yendell and Longstaff—British painters who “make art with their feet better than most people do with their hands”—perform most everyday tasks, including placing phone calls, buttoning up clothing and feeding themselves, with their toes.
To assess how this specialization affects the brain, Dempsey-Jones and her colleagues performed functional MRI scans on both artists. When the researchers stimulated each individual toe, they triggered activity in a corresponding area of the painters’ brains, revealing a foot pattern on par with two-handed individuals’ hand maps. When the team conducted similar tests on volunteers with typical arm and toe dexterity, however, they found that participants’ neural footprints showed up as solid regions with no distinction between toes.
If experts can find a way to replicate the painters’ neural flexibility, they may be able to apply their findings to such groups as stroke victims and individuals with cerebral palsy. By training the brain to better interact with individual body parts, scientists could help restore control to those without full use of their limbs; still, study co-author Wesselink says in a press release, it’s important to note that such brain mapping changes may only be possible during a small window of time—namely, when subjects are young and have “maximal brain plasticity.”
Wesselink concludes, “We know the adult brain is more fixed once the critical period of plasticity closes. It may be that once that happens you can't really change the brain in a major way, such as this.”