Augmented manipulation ability in humans with six-fingered hands

C Mehring,M Akselrod,O Blanke,R Salomon,M Blüher,H Choi,A Cheah,A Serino,L Bashford,A.-S Buschhoff,T Pistohl,M Mace,E Burdet

doi:10.1038/s41467-019-10306-w

Abstract

Neurotechnology attempts to develop supernumerary limbs, but can the human brain deal with the complexity to control an extra limb and yield advantages from it? Here, we analyzed the neuromechanics and manipulation abilities of two polydactyly subjects who each possess six fingers on their hands. Anatomical MRI of the supernumerary finger (SF) revealed that it is actuated by extra muscles and nerves, and fMRI identified a distinct cortical representation of the SF. In both subjects, the SF was able to move independently from the other fingers. Polydactyly subjects were able to coordinate the SF with their other fingers for more complex movements than five fingered subjects, and so carry out with only one hand tasks normally requiring two hands. These results demonstrate that a body with significantly more degrees-of-freedom can be controlled by the human nervous system without causing motor deficits or impairments and can instead provide superior manipulation abilities.

Highlights

Neurotechnology attempts to develop supernumerary limbs, but can the human brain deal with the complexity to control an extra limb and yield advantages from it? Here, we analyzed the neuromechanics and manipulation abilities of two polydactyly subjects who each possess six fingers on their hands
Is the human brain able to control a body with additional degrees-of-freedom, as the range of possible movements increases exponentially with every dof, and could this enhance functional abilities? how can the nervous system represent an extra limb and its relation to other limbs? The challenging, massive reorganization of neural representation required for individuals with abnormal body structure is illustrated through phantom limbs experienced by amputees[7,8]
The neuromechanics and functionality of polydactyly hands raise many questions that have never been investigated: First, is the movement of the additional finger actuated by other fingers’. Muscles, or does it have its own dedicated muscles and nerves? Second, how independent is the extra finger from the other fingers? Does its movement accompany the movement of common fingers, like in the little and ring fingers[14], or does it move independently from other fingers like the thumb? Third, hand movements are already among the most complex movements humans can perform, requiring a large area of the sensory and motor cortices to control them[14,15,16]