Brain activity in supernumerary people gives a new insight into the robotic limb

Worldwide, about one in every 500 babies is born with extra fingers or toes – a condition called polydactyly. Often referred to as a "conbad anomaly", extra digits are usually removed soon after birth.

Research on polydactyly has focused primarily on the genetic mutation that underpinned it, but so far no one has studied how the brain and body compensate for the workload extra when the extra digits are functional.

New research from the University of Freiburg, Imperial College London and the University of Lausanne has revealed that the brain badigns dedicated areas to additional digits, which makes them as useful as the standard figures.

The authors believe that studying the brain of polydactyls could teach us how our brain adapts to an extra workload.

Each of our fingers is connected to the hand by dedicated tendons, moved by dedicated muscles and connected to dedicated nerves – which are all specific to each finger. These are controlled by brain areas specific to each finger of the motor cortex, the brain region responsible for movement.

The researchers wanted to know how the additional figures fit into this arrangement.

Professor Etienne Burdet, lead author of the study, said, "Excessive fingers and toes are traditionally considered a conbad malformation; no one has thought of studying their real utility. "

Two people were studied: a 52-year-old woman and her 17-year-old son, both of whom have six fingers on each of their hands, with an extra finger well formed between the thumb and index fingers.

Researchers asked subjects to explore objects with their hands, tie laces, type on the phone, and play video games – all of which are referred to as "manipulations."

They badyzed and compared movements to control subjects' movements with five fingers on each hand. During manipulation, high resolution functional magnetic resonance imaging (fMRI) monitored their brain activity.

The researchers found that, like non-polydactyl fingers, the extra fingers had their own specific tendons, muscles, and nerves, as well as additional corresponding brain regions in the motor cortex.

Polydactyl participants also performed better than their non-polydactyl counterparts. For example, they were able to perform certain tasks, such as tie laces, with one hand, when two are usually needed.

Although additional finger control required additional work for the brain, both subjects had no obvious cognitive discomfort.

Professor Burdet said, "The brain of each polydactyl was well suited to controlling the extra workload and even had extra finger areas. It's amazing that the brain has the ability to do so apparently without borrowing resources from other sources. "

The authors say the findings could serve as a model for the development of artificial limbs and figures to increase our natural movement capabilities. For example, giving a surgeon control of an additional robotic arm could allow him to function without an badistant.

Professor Carsten Mehring of the University of Freiburg, lead author, said: "We could perhaps exploit the brain resources demonstrated in this study to make this possible."

However, he also warned that people with additional robotic limbs might not get as effective control as observed in both polydactyl subjects.

The fingers or the robotic members would not have a bone structure, muscles, tendons or dedicated nerves. In addition, subjects should learn to use extra fingers or limbs, much like an amputee learning to use a prosthetic arm.

Prof. Mehring added: "In our study, additional figures were formed on subjects since birth. This does not necessarily mean that similar functionality can be achieved when artificial limbs are added later in life.

"Yet, people with polydactyly provide a unique opportunity to badyze the neural control of additional limbs and the possibilities of enhancing sensorimotor control."