The extra finger allows people to perform one-handed movements that people with five fingers would need two.
Polydactyly - having more than five fingers or toes. It occurs due to mutations in four different genes and is the most common inherited limb abnormality. A new study by scientists from the University of Freiburg, Imperial College London and University Hospital Lausanne shows for the first time the motor skills of people with polydactyly and changes in their sensorimotor areas.
Scientists conducted a study of two people with six fingers on their hands, whose extra finger was between the thumb and forefinger. In order to find out their abilities, the researchers forced them to pass several behavioral tests, while recording brain activity using functional magnetic resonance imaging (fMRI).
The results show that patients' extra fingers are controlled by their own muscles. This allows them to move their sixth finger independently of everyone else. It turned out that despite the fact that an extra finger increases the number of degrees of freedom that the brain must control, people with six fingers are in no way inferior to people with five. Scientists say it's amazing that the brain can do such things without sacrificing anything.
To understand how the brains of patients with polydactyly control extra fingers, the researchers used high-resolution functional magnetic resonance imaging. They found that there are dedicated extra neurons in the brain that control the sixth toe. It was also found that the somatosensory and motor cortex of these people is organized so that it is possible to control the sixth finger independently of the rest, expanding the manipulation abilities.
Studying the movements of people with polydactyly and their relationship with the activity of the cerebral cortex will help create new prostheses. For example, an extra arm will allow one person to work for two in a confined space, or help a surgeon perform operations without an assistant. However, as scientists note, the skills for controlling the sixth finger developed in the subjects from birth. It is not known how long it will take for an adult to train these skills.
Nikita Shevtsov