Surgically Implanted Electrodes Enable Real-Time Finger and Grasp Pattern Recognition for Prosthetic Hands

Currently available prosthetic hands are capable of actuating anywhere from five to 30 degrees of freedom (DOF). However, grasp control of these devices remains unintuitive and cumbersome. To address this issue, we propose directly extracting finger commands from the neuromuscular system via electrodes implanted in residual innervated muscles and regenerative peripheral nerve interfaces (RPNIs). Two persons with transradial amputations had RPNIs created by suturing autologous free muscle grafts to their transected median, ulnar, and dorsal radial sensory nerves. Bipolar electrodes were surgically implanted into their ulnar and median RPNIs and into their residual innervated muscles. The implanted electrodes recorded local electromyography (EMG) with Signal-to-Noise Ratios ranging from 23 to 350 measured across various movements. In a series of single-day experiments, participants used a high speed pattern recognition system to control a virtual prosthetic hand in real-time. Both participants were able to transition between 10 pseudo-randomly cued individual finger and wrist postures in the virtual environment with an average online accuracy of 86.5% and latency of 255 ms. When the set was reduced to five grasp postures, average metrics improved to 97.9% online accuracy and 135 ms latency. Virtual task performance remained stable across untrained static arm positions while supporting the weight of the prosthesis. Participants also used the high speed classifier to switch between robotic prosthetic grips and complete a functional performance assessment. These results demonstrate that pattern recognition systems can use the high-quality EMG afforded by intramuscular electrodes and RPNIs to provide users with fast and accurate grasp control.

SUMMARY

Surgically implanted electrodes recorded finger-specific electromyography enabling reliable finger and grasp control of an upper limb prosthesis.

Neural control of finger movement via intracortical brain-machine interface

OBJECTIVE

Intracortical brain-machine interfaces (BMIs) are a promising source of prosthesis control signals for individuals with severe motor disabilities. Previous BMI studies have primarily focused on predicting and controlling whole-arm movements; precise control of hand kinematics, however, has not been fully demonstrated. Here, we investigate the continuous decoding of precise finger movements in rhesus macaques.

APPROACH

In order to elicit precise and repeatable finger movements, we have developed a novel behavioral task paradigm which requires the subject to acquire virtual fingertip position targets. In the physical control condition, four rhesus macaques performed this task by moving all four fingers together in order to acquire a single target. This movement was equivalent to controlling the aperture of a power grasp. During this task performance, we recorded neural spikes from intracortical electrode arrays in primary motor cortex.

MAIN RESULTS

Using a standard Kalman filter, we could reconstruct continuous finger movement offline with an average correlation of ρ  =  0.78 between actual and predicted position across four rhesus macaques. For two of the monkeys, this movement prediction was performed in real-time to enable direct brain control of the virtual hand. Compared to physical control, neural control performance was slightly degraded; however, the monkeys were still able to successfully perform the task with an average target acquisition rate of 83.1%. The monkeys' ability to arbitrarily specify fingertip position was also quantified using an information throughput metric. During brain control task performance, the monkeys achieved an average 1.01 bits s-1 throughput, similar to that achieved in previous studies which decoded upper-arm movements to control computer cursors using a standard Kalman filter.

SIGNIFICANCE

This is, to our knowledge, the first demonstration of brain control of finger-level fine motor skills. We believe that these results represent an important step towards full and dexterous control of neural prosthetic devices.

Chronic recording of hand prosthesis control signals via a regenerative peripheral nerve interface in a rhesus macaque

OBJECTIVE

Loss of even part of the upper limb is a devastating injury. In order to fully restore natural function when lacking sufficient residual musculature, it is necessary to record directly from peripheral nerves. However, current approaches must make trade-offs between signal quality and longevity which limit their clinical potential. To address this issue, we have developed the regenerative peripheral nerve interface (RPNI) and tested its use in non-human primates.

APPROACH

The RPNI consists of a small, autologous partial muscle graft reinnervated by a transected peripheral nerve branch. After reinnervation, the graft acts as a bioamplifier for descending motor commands in the nerve, enabling long-term recording of high signal-to-noise ratio (SNR), functionally-specific electromyographic (EMG) signals. We implanted nine RPNIs on separate branches of the median and radial nerves in two rhesus macaques who were trained to perform cued finger movements.

MAIN RESULTS

No adverse events were noted in either monkey, and we recorded normal EMG with high SNR (>8) from the RPNIs for up to 20 months post-implantation. Using RPNI signals recorded during the behavioral task, we were able to classify each monkey's finger movements as flexion, extension, or rest with >96% accuracy. RPNI signals also enabled functional prosthetic control, allowing the monkeys to perform the same behavioral task equally well with either physical finger movements or RPNI-based movement classifications.

SIGNIFICANCE

The RPNI signal strength, stability, and longevity demonstrated here represents a promising method for controlling advanced prosthetic limbs and fully restoring natural movement.

Recent avian influenza virus A/H5N1 evolution in vaccinated and unvaccinated poultry from farms in Southern Vietnam, January-March 2010

We report 15 new avian influenza virus A/H5N1 haemagglutinin (HA) sequences sampled from visibly sick domestic poultry in southern Vietnam, between 1 January 2010 and 6 March 2010. These HA sequences form a new sub-clade of the clade 1 H5N1 viruses that have been circulating in Vietnam since 2003/2004. The viruses are characterized by a change from isoleucine to valine at position 514 (I514V) and are 1.8% divergent at the nucleotide level from HA sequences sampled in Vietnam in 2007. Five new amino acid changes were observed at previously identified antigenic sites, and three were located within structural elements of the receptor-binding domain. One new mutation removed a potential N-linked glycosylation site, and a methionine insertion was observed in one virus at the polybasic cleavage site. Five of these viruses were sampled from farms where poultry were vaccinated against H5N1, but there was no association between observed amino acid changes and flock vaccination status. Despite the current lack of evidence for antigenic drift or immune escape in Vietnamese H5N1 viruses, continued surveillance remains a high priority.

Yemen and Vietnam capripoxviruses demonstrate a distinct host preference for goats compared with sheep

Sheeppox and goatpox are caused by viruses that are members of the genus Capripoxvirus, and globally result in significant production losses. To improve the understanding of disease pathogenesis and evaluate host species preferences, sheep and goats were inoculated either with a capripoxvirus isolate from Yemen or from a recent outbreak in Vietnam. Blood, swabs and tissues were collected at various time points following experimental challenge and assessed for viral DNA content using real-time PCR and infectivity using virus isolation. The Yemen isolate was considerably more pathogenic in goats with 100 % mortality and morbidity compared with sheep with 0 % mortality and 100 % morbidity. The Vietnam isolate was also more pathogenic in goats with 100 % morbidity and an estimated 33 % mortality rate compared with mild morbidity and a 0 % mortality rate in sheep. Higher viral titres were observed in nasal, oral and conjunctival swabs from goats inoculated with either the Yemen or Vietnam isolate compared with those collected from sheep. Although the highest viral titres were detected in primary and secondary skin lesions in sheep and goats, the severity of clinical disease observed in each species varied according to the inoculum used. Whereas both the Yemen and Vietnam isolates clearly caused more severe disease in goats, the Yemen isolate was also moderately pathogenic in sheep. The Vietnam isolate, in contrast, caused only very mild disease in sheep. Limited DNA sequencing revealed ORF 074 of the Vietnam isolate to be identical to that of several goatpox virus isolates from China, suggesting a possible Chinese origin.

Eccrine poroma of the eyelid

A clinicopathological case report of a 71-year-old Caucasoid man with an unusual right lower eyelid lesion, which proved to be an eccrine poroma, is presented. Benign eccrine poromas have not previously been reported to occur on the eyelid. Compete surgical excision of this lesion proved to be curative, with no recurrence after 3 years follow up. Eccrine poromas are common benign tumours of the intraepidermal sweat duct unit. Sweat glands occur commonly on the eyelids and eccrine poroma should be considered in the differential diagnosis of eyelid tumours.