Robotic hand augmentation drives changes in neural body representation

Abstract

Humans have long been fascinated by the opportunities afforded through augmentation. This vision not only depends on technological innovations but also critically relies on our brain’s ability to learn, adapt, and interface with augmentation devices. Here, we investigated whether successful motor augmentation with an extra robotic thumb can be achieved and what its implications are on the neural representation and function of the biological hand. Able-bodied participants were trained to use an extra robotic thumb (called the Third Thumb) over 5 days, including both lab-based and unstructured daily use. We challenged participants to complete normally bimanual tasks using only the augmented hand and examined their ability to develop hand-robot interactions. Participants were tested on a variety of behavioral and brain imaging tests, designed to interrogate the augmented hand’s representation before and after the training. Training improved Third Thumb motor control, dexterity, and hand-robot coordination, even when cognitive load was increased or when vision was occluded. It also resulted in increased sense of embodiment over the Third Thumb. Consequently, augmentation influenced key aspects of hand representation and motor control. Third Thumb usage weakened natural kinematic synergies of the biological hand. Furthermore, brain decoding revealed a mild collapse of the augmented hand’s motor representation after training, even while the Third Thumb was not worn. Together, our findings demonstrate that motor augmentation can be readily achieved, with potential for flexible use, reduced cognitive reliance, and increased sense of embodiment. Yet, augmentation may incur changes to the biological hand representation. Such neurocognitive consequences are crucial for successful implementation of future augmentation technologies.

Assessment and Brain Training of Patients Experiencing Head and Facial Pain with a Distortion of Orofacial Somatorepresentation: A Narrative Review

“…Changes in perception and activation of brain areas have been demonstrated, from the rubber hand illusion until the third thumb experiment, where a cortical integration of the extra thumb achieved activation of neural pathways due to the fake thumb, leading to a neuroplastic process of the SNC reaching a greater body representation [145]. In this way, the combination of sensory and visual stimuli seems an interesting option to generate neuroplastic changes, based in an attentional intervention where the tactile stimuli will be integrated together with the visual feedback [146,147].…”

Design, Construction and Tests of a Low-Cost Myoelectric Thumb

“…Another difference to Ref. [27] is that here not the big toe, but an arm muscle was used to control the third thumb, making a comparison of training effects complicated. The extra robotic thumb described in Ref.…”

“…The latter had a higher degree of freedom, making movements more reliable, but nevertheless has to be developed further to reduce undesired movements due to noise. It should be mentioned that this project mainly aimed at producing a customized low-cost myoelectric prosthesis, without applying brain related measured or investigating the effect of training, as the aforementioned studies on using a third thumb did [27,28]. Another difference to Ref.…”

“…Besides these and other low-cost prostheses, there are also attempts to train people with neurological injuries or to extend the physical properties of non-handicapped people by exoskeletons [23][24][25]. Regarding hands or fingers, there are a few studies and design approaches investigating the effect of a third thumb, e.g., controlled by the feet [26], allowing to give people extended motor skills and at the same time enabling neuro-scientific research on neuroplasticity [27,28].…”

Beyond body maps: information content of specific body parts is distributed across the somatosensory Homunculus

“…A node approximately 1cm below and above the hand knob was defined as an anatomical hand sub-region. Note that this criterion defined a more conservative hand region than was done in previous work (Wiestler and Diedrichsen, 2013; Wesselink et al ., 2019; Kieliba et al ., 2021). A gap of 1cm was then defined above and below this anatomical hand sub-region, and the remaining medial and lateral parts of S1 were used as the other two anatomical sub-regions.…”