Broadband Prosthetic Interfaces: Combining Nerve Transfers and Implantable Multichannel EMG Technology to Decode Spinal Motor Neuron Activity

Abstract

Modern robotic hands/upper limbs may replace multiple degrees of freedom of extremity function. However, their intuitive use requires a high number of control signals, which current man-machine interfaces do not provide. Here, we discuss a broadband control interface that combines targeted muscle reinnervation, implantable multichannel electromyographic sensors, and advanced decoding to address the increasing capabilities of modern robotic limbs. With targeted muscle reinnervation, nerves that have lost their targets due to an amputation are surgically transferred to residual stump muscles to increase the number of intuitive prosthetic control signals. This surgery re-establishes a nerve-muscle connection that is used for sensing nerve activity with myoelectric interfaces. Moreover, the nerve transfer determines neurophysiological effects, such as muscular hyper-reinnervation and cortical reafferentation that can be exploited by the myoelectric interface. Modern implantable multichannel EMG sensors provide signals from which it is possible to disentangle the behavior of single motor neurons. Recent studies have shown that the neural drive to muscles can be decoded from these signals and thereby the user's intention can be reliably estimated. By combining these concepts in chronic implants and embedded electronics, we believe that it is in principle possible to establish a broadband man-machine interface, with specific applications in prosthesis control. This perspective illustrates this concept, based on combining advanced surgical techniques with recording hardware and processing algorithms. Here we describe the scientific evidence for this concept, current state of investigations, challenges, and alternative approaches to improve current prosthetic interfaces.

Bionic Upper Limb Reconstruction: A Valuable Alternative in Global Brachial Plexus Avulsion Injuries—A Case Series

“…These few motor axons may then be used to re-innervate a free muscle transplant transferred to the patient s arm, which will not have the functional capacity or power of a biological muscle but instead serve as an additional EMG signal for future prosthetic control (given that a sufficient number of axons regenerate into the transferred muscle target). Since the dexterity of prosthetic control increases with the number of available EMG signals [18,19], free functional muscle transfers have previously been used to increase the number of these muscle signals [16].…”

Bionic hand as artificial organ: Current status and future perspectives

“…Although previous studies indicate substantial changes within the motor unit, so far, the effects of such a “high capacity” donor nerve transfer remain mainly unknown . Kuiken et al found a hyperreinnervation of the muscle after TMR procedure, leading to enhanced axonal input of motoneurons.…”

“…Muceli et al showed promising results with an implantable multichannel electrode, which is also capable of recording down to single motor units in combination with all the benefits of implantable devices. Further research will reveal possible implementation, although demand is granted …”

“…But not only the surplus of signals created by TMR is important, also the surplus of motor unit information can be used, combined with capable interface technology for a sophisticated control . Multichannel technology for high resolution of motor unit behavior will play an important role in future sophisticated interfacing devices …”

Experimental Testing of Bionic Peripheral Nerve and Muscle Interfaces: Animal Model Considerations

“…Since its introduction in the 1940s, the standard approach to interfacing is the use of few muscle-control signals recorded by surface EMG electrodes (Bergmeister et al, 2017). With this classic approach, two signals are used to control multiple degrees of freedom, often resulting in non-intuitive control (Farina and Aszmann, 2014).…”