Direct neural sensory feedback and control of a prosthetic arm

Control strategies for smart prosthetic hand technology: an overview

A chronological overview of the applications of control theory to prosthetic hand is presented. The overview focuses on hard computing or control techniques such as multivariable feedback, optimal, nonlinear, adaptive and robust and soft computing or control techniques such as artificial intelligence, neural networks, fuzzy logic, genetic algorithms and on the fusion of hard and soft control techniques. This overview is not intended to be an exhaustive survey on this topic and any omissions of other works is purely unintentional.

Sensory capacity of reinnervated skin after redirection of amputated upper limb nerves to the chest

Targeted reinnervation is a new neural-machine interface that has been developed to help improve the function of new-generation prosthetic limbs. Targeted reinnervation is a surgical procedure that takes the nerves that once innervated a severed limb and redirects them to proximal muscle and skin sites. The sensory afferents of the redirected nerves reinnervate the skin overlying the transfer site. This creates a sensory expression of the missing limb in the amputee's reinnervated skin. When these individuals are touched on this reinnervated skin they feel as though they are being touched on their missing limb. Targeted reinnervation takes nerves that once served the hand, a skin region of high functional importance, and redirects them to less functionally relevant skin areas adjacent to the amputation site. In an effort to better understand the sensory capacity of the reinnervated target skin following this procedure, we examined grating orientation thresholds and point localization thresholds on two amputees who had undergone the targeted reinnervation surgery. Grating orientation thresholds and point localization thresholds were also measured on the contralateral normal skin of the targeted reinnervation amputees and on analogous sites in able-bodied controls. Grating orientation thresholds for the reinnervated skin of the targeted reinnervation amputees were found to be similar to normal ranges for both the amputees' contralateral skin and also for the control population. Point localization thresholds for these amputees were found to be lower for their reinnervated skin than for their contralateral skin. Reinnervated point localization thresholds values were also lower in comparison to homologous chest sites on the control population. Mechanisms appear to be in place to maximize re-established touch input in targeted reinnervation amputees. It seems that sound sensory function is provided to the denervated skin of the residual limb when connected to afferent pathways once serving highly functionally relevant regions of the brain. This suggests that tactile interface devices could be used to give a physiologically appropriate sense of touch to a prosthetic limb, which would likely help with better functional utilization of the prosthetic device and possibly help to more effectively integrate the device with the user's self-image.

Consumer design priorities for upper limb prosthetics

PURPOSE

To measure consumer satisfaction with upper limb prosthetics and provide an enumerated list of design priorities for future developments.

METHODS

A self-administered, anonymous survey collected information on participant demographics, history of and goals for prosthesis use, satisfaction, and design priorities. The questionnaire was available online and in paper format and was distributed through healthcare providers, community support groups, and one prosthesis manufacturer; 242 participants of all ages and levels of upper limb absence completed the survey.

RESULTS

Rates of rejection for myoelectric hands, passive hands, and body-powered hooks were 39%, 53%, and 50%, respectively. Prosthesis wearers were generally satisfied with their devices while prosthesis rejecters were dissatisfied. Reduced prosthesis weight emerged as the highest priority design concern of consumers. Lower cost ranked within the top five design priorities for adult wearers of all device types. Life-like appearance is a priority for passive/cosmetic prostheses, while improved harness comfort, wrist movement, grip control and strength are required for body-powered devices. Glove durability, lack of sensory feedback, and poor dexterity were also identified as design priorities for electric devices.

CONCLUSIONS

Design priorities reflect consumer goals for prosthesis use and vary depending on the type of prosthesis used and age. Future design efforts should focus on the development of more light-weight, comfortable prostheses.

On the use of longitudinal intrafascicular peripheral interfaces for the control of cybernetic hand prostheses in amputees

Significant strides have been recently made to develop highly sensorized cybernetic prostheses aimed at restoring sensorimotor limb functions to those who have lost them because of a traumatic event (amputation). In these cases, one of the main goals is to create a bidirectional link between the artificial devices (e.g., robotic hands, arms, or legs) and the nervous system. Several human-machine interfaces (HMIs) are currently used to this aim. Among them, interfaces with the peripheral nervous system and in particular longitudinal intrafascicular electrodes can be a promising solution able to improve the current situation. In this paper, the potentials and limits of the use of this interface to control robotic devices are presented. Specific information is provided on: 1) the neurophysiological bases for the use peripheral nerve interfaces; 2) a comparison of the potentials of the different peripheral neural interfaces; 3) the possibility of extracting and appropriately interpreting the neural code for motor commands and of delivering sensory feedback by stimulating afferent fibers by using longitudinal intrafascicular electrodes; 4) a preliminary comparative analysis of the performance of this approach with the ones of others HMIs; 5) the open issues which have to be addressed for a chronic usability of this approach.

On the control of a robot hand by extracting neural signals from the PNS: preliminary results from a human implantation

The development of hybrid neuroprosthetic systems (HBSs) linking the human nervous system with artificial devices is an important area of research that is currently addressed by several groups to restore sensorimotor function in people affected by different disabilities. It is particularly important to establish a fast, intuitive, bidirectional flow of information between the nervous system of the user and the smart robotic device. Among the possible solutions to achieve this goal, interfaces with the peripheral nervous system and in particular intraneural electrodes can represent an interesting choice. In the present study, thin-film longitudinal intra-fascicular electrodes were implanted in the median and ulnar nerves of an amputee. The possibility of restoring the bidirectional link between the subject and the external world was investigated during a 4 week trial. The result showed that both the extraction of motor information and the restoration of sensory function are possible.

Improved long-term recording of nerve signal by modified intrafascicular electrodes in rabbits

Methods for long-term recording of peripheral nerve activity via intrafascicular electrodes have not been optimized. We compared the long-term functionality of custom-made 95%Pt/5%Ir intrafascicular electrodes containing a proximal spring-like structure to that of conventional straight electrodes. The modified electrode was implanted into the sciatic nerve fascicle of a random hind limb in 14 rabbits for 9 months. A conventional electrode was implanted in the opposite hind limb as a control. Orthodromic and antidromic nerve potentials were sampled and analyzed monthly. Latency, amplitude, and nerve conduction velocity of electrical signals were generally similar within the modified group and straight control group at different time intervals (P > 0.05). However, at the conclusion of the study period, the modified electrode group had a greater number of functioning electrodes (P < 0.05) and a greater total functioning electrode time (P = 0.006). Intrafascicular electrodes with a spring-like structure demonstrated superior potential for long-term electrophysiological monitoring over straight electrodes.

A charge-balanced pulse generator for nerve stimulation applications

Nerve stimulation typically employs charge-balanced current injection with a delay between the cathodal and anodal phases. Typically these waveforms are produced using a microprocessor. However, once appropriate stimulus parameters are chosen, they tend to remain fixed within an application, making computational power unnecessary. In such cases, it would be advantageous to replace the microprocessor with integrated circuitry and hardware controls for maintaining fixed pulse parameters. We describe here an architecture that generates controllable charge-balanced pulses but requires no computer processing components. The circuitry has been engineered such that minimum size and power consumption can be achieved when fabricated into an IC chip, making it ideal for many long term, portable nerve stimulation devices and applications.

Upper limb prosthesis use and abandonment: a survey of the last 25 years

This review presents an analytical and comparative survey of upper limb prosthesis acceptance and abandonment as documented over the past 25 years, detailing areas of consumer dissatisfaction and ongoing technological advancements. English-language articles were identified in a search of Ovid, PubMed, and ISI Web of Science (1980 until February 2006) for key words upper limb and prosthesis. Articles focused on upper limb prostheses and addressing: (i) Factors associated with abandonment; (ii) Rejection rates; (iii) Functional analyses and patterns of wear; and (iv) Consumer satisfaction, were extracted with the exclusion of those detailing tools for outcome measurement, case studies, and medical procedures. Approximately 200 articles were included in the review process with 40 providing rates of prosthesis rejection. Quantitative measures of population characteristics, study methodology, and prostheses in use were extracted from each article. Mean rejection rates of 45% and 35% were observed in the literature for body-powered and electric prostheses respectively in pediatric populations. Significantly lower rates of rejection for both body-powered (26%) and electric (23%) devices were observed in adult populations while the average incidence of non-wear was similar for pediatric (16%) and adult (20%) populations. Documented rates of rejection exhibit a wide range of variance, possibly due to the heterogeneous samples involved and methodological differences between studies. Future research should comprise of controlled, multifactor studies adopting standardized outcome measures in order to promote comprehensive understanding of the factors affecting prosthesis use and abandonment. An enhanced understanding of these factors is needed to optimize prescription practices, guide design efforts, and satiate demand for evidence-based measures of intervention.

Technology Insight: future neuroprosthetic therapies for disorders of the nervous system

Most disorders of the nervous system result from localized sensory or motor pathologies attributable to disease or trauma. The emerging field of neuroprosthetics is focused on the development of therapeutic interventions that will be able to restore some of this lost neural function by selective electrical stimulation of sensory or motor pathways, or by harnessing activity recorded from remnant neural pathways. A key element in this restoration of function has been the development of a new generation of penetrating microelectrode arrays that provide unprecedented selective access to the neurons of the CNS and PNS. The active tips of these microelectrode arrays penetrate the nervous tissues and abut against small populations of neurons or nerve fibers, thereby providing selective access to these cells. These electrode arrays are not only beginning to provide researchers with the ability to better study the spatiotemporal information processing performed by the nervous system, they can also form the basis for new therapies for disorders of the nervous system. In this Review, three examples of this new generation of microelectrode arrays are described, as are potential therapeutic applications in blindness and spinal cord injury, and for the control of prosthetic limbs.

Residual motor signal in long-term human severed peripheral nerves and feasibility of neural signal-controlled artificial limb

PURPOSE

The residual motor pathways after amputation have not been fully elucidated. We sampled potentials from peripheral nerve stumps with intrafascicular electrodes to study residual motor transmission and explore the feasibility of nerve signal-controlled artificial limbs.

METHODS

Six intrafascicular electrodes were inserted into the ulnar, radial, and median nerves in the stump of an amputee. An electrode was placed outside the fascicle as a reference. Potentials from 4 of the 6 electrodes per trial were monitored using a 4-channel electromyogram machine, and 32 groups of electrophysiologic tests were conducted under volitional control. Actions included finger extension and flexion, forearm pronation and supination, and wrist extension and flexion. Each action was carried out with light, intermediate, and full efforts. Then, 2 of 6 electrodes randomly chosen per trial were interfaced to a nerve signal-controlled artificial limb. Finger extension and flexion of the prosthesis were tested under volitional control.

RESULTS

The volitional motor nerve potentials uniquely associated with the missing limb were recorded successfully with intrafascicular electrodes. The signal amplitude from the radial nerve was 5.5 microV +/- 0.8 (mean +/- SD), which was greater than the amplitudes from the ulnar (2.5 microV +/- 0.4) and median (2.2 microV +/- 0.3) nerves. Under volitional control of the subject, finger extension of the artificial limb was triggered by the radial nerve signal, but the remaining actions were unsuccessful.

CONCLUSIONS

The long-term amputee was able to generate motor neuron activity related to phantom limb movement. Intrafascicular electrodes can be used to monitor residual motor nerve activity in the stump, and the amplitude may predict successful control of artificial limbs.

Digital emulation of pulse frequency modulation for neuroprosthetic sensory feedback

Pulse frequency modulation (PFM) is a method of encoding information where the instantaneous frequency of a pulse train carries the signal's information. PFM is of particular interest to those working towards interfacing prosthetic devices directly with the human nervous system. In this paper, we consider the effects of directly implementing PFM with a digital microprocessor. We consider three digital PFM algorithms: two are deterministic, and the third has a probabilistic nature that has desirable time-averaged and ensemble behavior. For each algorithm, we analytically bound the error between the desired pulse frequency and the actual frequency output by the microprocessor. We aim to provide tools for the design and analysis of closed-loop neuroprosthetic systems containing PFM.

Neural machine interfaces for controlling multifunctional powered upper-limb prostheses

This article investigates various neural machine interfaces for voluntary control of externally powered upper-limb prostheses. Epidemiology of upper limb amputation, as well as prescription and follow-up studies of externally powered upper-limb prostheses are discussed. The use of electromyographic interfaces and peripheral nerve interfaces for prosthetic control, as well as brain machine interfaces suitable for prosthetic control, are examined in detail along with available clinical results. In addition, studies on interfaces using muscle acoustic and mechanical properties and the problem of interfacing sensory information to the nervous system are discussed.

Implantation mechanics of tungsten microneedles into peripheral nerve trunks

50 microm tungsten microneedles have been used as a means to introduce longitudinal intra-fascicular electrodes (LIFE) into small peripheral nerve fascicles. However, recent attempts to implant LIFEs into larger, human sized nerves with the same needles resulted in buckling failure of the introducer needle. In the present study, the implantation mechanics (penetration forces and penetration dimple depth) of electrosharpened tungsten microneedles ranging in diameters from 50 to 200 microm into freshly excised porcine peripheral nerve trunks between 3 and 5 mm in thickness was characterized to understand the implantation mechanics and to find the minimum needle diameter that would result in successful penetration. The implant success rate was found to be highest with needles having diameters between 80 and 120 microm. The force of successful penetration ranged from 7.2 +/- 0.6 to 71.8 +/- 19.5 mN, and increased monotonically with needle diameter. It also had a tendency to increase with increasing tip angles. The dimple depth for successful penetrations varied between 1 and 1.5 mm, and also tended to increase with increasing tip angles, although it was generally not affected by increased needle diameter. Only the smallest penetration dimple depth was found to be different from the others and was associated with the smallest diameter needle (50 microm). Analysis based on the critical buckling force and the measured implantation forces indicated a 15 mm long needle of 80 microm diameter would be necessary and sufficient to penetrate medium to large sized nerves.

Targeted reinnervation for enhanced prosthetic arm function in a woman with a proximal amputation: a case study

BACKGROUND

The function of current artificial arms is limited by inadequate control methods. We developed a technique that used nerve transfers to muscle to develop new electromyogram control signals and nerve transfers to skin, to provide a pathway for cutaneous sensory feedback to the missing hand.

METHODS

We did targeted reinnervation surgery on a woman with a left arm amputation at the humeral neck. The ulnar, median, musculocutaneous, and distal radial nerves were transferred to separate segments of her pectoral and serratus muscles. Two sensory nerves were cut and the distal ends were anastomosed to the ulnar and median nerves. After full recovery the patient was fit with a new prosthesis using the additional targeted muscle reinnervation sites. Functional testing was done and sensation in the reinnervated skin was quantified.

FINDINGS

The patient described the control as intuitive; she thought about using her hand or elbow and the prosthesis responded appropriately. Functional testing showed substantial improvement: mean scores in the blocks and box test increased from 4.0 (SD 1.0) with the conventional prosthesis to 15.6 (1.5) with the new prosthesis. Assessment of Motor and Process Skills test scores increased from 0.30 to 1.98 for motor skills and from 0.90 to 1.98 for process skills. The denervated anterior chest skin was reinnervated by both the ulnar and median nerves; the patient felt that her hand was being touched when this chest skin was touched, with near-normal thresholds in all sensory modalities.

INTERPRETATION

Targeted reinnervation improved prosthetic function and ease of use in this patient. Targeted sensory reinnervation provides a potential pathway for meaningful sensory feedback.

„Bionische“ Armprothesen

BACKGROUND

A new generation of arm prostheses is being developed worldwide. These so-called bionic prostheses are intended to offer additional functions, such as sensory feedback, extended range of possible movement, intuitive movement control as far as possible, and a more natural cosmetic appearance.

STATE OF THE ART IN RESEARCH AND DEVELOPMENT

In recent years, prosthetic components with much enhanced performance have been developed for use at various levels of the upper limb. Artificial hands that allow for additional grips are are being tested in clinical settings. Innovative methods of signal acquisition and communication with the patient are being intensively researched.

CONCLUSION

Several patients have been provided with prototypes of new arm prostheses. At the moment, the results are limited by the restricted communication between patient and prosthesis. However, we can expect the options for prosthesis control to be extended in the near future.

Brain-Controlled Interfaces: Movement Restoration with Neural Prosthetics

Brain-controlled interfaces are devices that capture brain transmissions involved in a subject's intention to act, with the potential to restore communication and movement to those who are immobilized. Current devices record electrical activity from the scalp, on the surface of the brain, and within the cerebral cortex. These signals are being translated to command signals driving prosthetic limbs and computer displays. Somatosensory feedback is being added to this control as generated behaviors become more complex. New technology to engineer the tissue-electrode interface, electrode design, and extraction algorithms to transform the recorded signal to movement will help translate exciting laboratory demonstrations to patient practice in the near future.