How Can Handless People Use the Hands-Feet?

Besides having "four hands", monkeys are also known for their imitation ability, which we, humans, the two-handed monkeys, too, have it, even if we display it a bit more discreetly. Besides executing the slightest muscular contraction when accomplishing a task, our brains fire up the same pathways needed to perform any action we see performed by another person.

Still, a new research points to the fact that the brain can employ alternate circuits when dealing with an action the body cannot physically copy. Thus, the brain's motor system rather attends to achieve a goal than just duplicate a movement neuronal pathway.

When you watch someone playing a game or using a tool, brain nuclei unconsciously respond, making a map of what you see translated into the motor pathways you would need to carry out that movements. This is named mirror neuron system, made of a type of motor neurons, and which is crucial for learning and developing new behaviors and skills like recognizing facial mimics.

In this new approach, the Dutch-Italian-French team could check how the brain reacts if the body lacks the ability to closely copy the action. The team presented videos of hands accomplishing simple actions, like grasping a cup, to 16 "normal" people and two aplastic people, born with missing hands or arms. During all this time, the researchers scanned the subjects' brains using fMRI. The normally developed people activated the common motor pathways required for holding a cup.

"The aplasic people activated motor pathways too, but not the same ones," said senior author Christian Keysers, neuroscientist at the University of Groningen in the Netherlands.

"Their brains lit up in regions needed for moving the feet. The results underscore that the mirror neuron system isn't mindlessly imitating, but working toward a goal. The two people without hands or arms recognized they could lift a cup with their feet--and their brain lit up accordingly." he said.

This research proves that "the role of mirror neurons is to let us mirror people, not just actions. However, there is a great deal of variability in the level and location of brain activity in both groups. Without a larger study, it's impossible to determine whether these phantom movements are universal." said Marco Iacoboni, a neuroscientist at the University of California, Los Angeles.