Elsevier

The Lancet

Volume 381, Issue 9866, 16–22 February 2013, Pages 557-564
The Lancet

Articles
High-performance neuroprosthetic control by an individual with tetraplegia

https://doi.org/10.1016/S0140-6736(12)61816-9Get rights and content

Summary

Background

Paralysis or amputation of an arm results in the loss of the ability to orient the hand and grasp, manipulate, and carry objects, functions that are essential for activities of daily living. Brain–machine interfaces could provide a solution to restoring many of these lost functions. We therefore tested whether an individual with tetraplegia could rapidly achieve neurological control of a high-performance prosthetic limb using this type of an interface.

Methods

We implanted two 96-channel intracortical microelectrodes in the motor cortex of a 52-year-old individual with tetraplegia. Brain–machine-interface training was done for 13 weeks with the goal of controlling an anthropomorphic prosthetic limb with seven degrees of freedom (three-dimensional translation, three-dimensional orientation, one-dimensional grasping). The participant's ability to control the prosthetic limb was assessed with clinical measures of upper limb function. This study is registered with ClinicalTrials.gov, NCT01364480.

Findings

The participant was able to move the prosthetic limb freely in the three-dimensional workspace on the second day of training. After 13 weeks, robust seven-dimensional movements were performed routinely. Mean success rate on target-based reaching tasks was 91·6% (SD 4·4) versus median chance level 6·2% (95% CI 2·0–15·3). Improvements were seen in completion time (decreased from a mean of 148 s [SD 60] to 112 s [6]) and path efficiency (increased from 0·30 [0·04] to 0·38 [0·02]). The participant was also able to use the prosthetic limb to do skilful and coordinated reach and grasp movements that resulted in clinically significant gains in tests of upper limb function. No adverse events were reported.

Interpretation

With continued development of neuroprosthetic limbs, individuals with long-term paralysis could recover the natural and intuitive command signals for hand placement, orientation, and reaching, allowing them to perform activities of daily living.

Funding

Defense Advanced Research Projects Agency, National Institutes of Health, Department of Veterans Affairs, and UPMC Rehabilitation Institute.

Introduction

Brain–machine interfaces transform neural activity into control signals for an external device. Functional electrical stimulators, exoskeletons, and sophisticated prosthetic limbs are being developed with the goal of restoring natural function. For many activities of daily living, an individual needs to be able to position the hand in space, orient the palm, and grasp an object. These hand movements are normally smoothly coordinated and follow the general principles of natural movement.1, 2, 3 Ideally a brain–machine interface will translate neural activity into control of an external device with the capability of producing natural movements in accordance with the general principles.

The natural features of movement have been captured in recordings of motor cortical neural activity using intracortical microelectrodes in a study in non-human primates.4 In other animal studies, a robot arm was controlled in four dimensions for self-feeding tasks5 and in seven dimensions for orientation and grasping.6 Motor cortical activity has also been used to electrically activate paralysed muscles of the upper limb.7, 8 Results of studies in people have shown three-dimensional translational control,9, 10, 11 and control over a single grasping dimension.12 We therefore tested whether an individual with tetraplegia could rapidly achieve control of a state-of-the-art anthropomorphic prosthetic limb (modular prosthetic limb [MPL], Johns Hopkins University, Applied Physics Laboratory, Baltimore, MD, USA).

Section snippets

Participant

The participant was a 52-year-old woman who was diagnosed with spinocerebellar degeneration 13 years before she took part in this study. Thorough chart review and discussions with her neurologist showed no indication of cerebellar involvement. The participant's injury was motor complete with manual muscle test scores 0 of 5 for the upper limb.13 Physical examination showed that she had generally intact sensation with some hypersensitivity.

This study was approved by the institutional review

Results

The arrays were implanted on Feb 10, 2012, and the first day of testing was on Feb 20, 2012. The last day of testing was May 18, 2012. The range of recorded single-unit and multi-unit neural activity was from 209 units per day to 271 units per day (figure 2). There seemed to be an initial settling period during which the number of units started off high until day 21 after the implant and then fell in week 4 (day 24). Starting at day 24, the neural activity began to increase linearly at a rate

Discussion

In this study, an individual with tetraplegia rapidly learned to routinely reach and grasp using coordinated and robust seven-dimensional control (three-dimensional translation, three-dimensional orientation, one-dimensional grasping) of a high-performance anthropomorphic prosthetic limb. The participant did the manoeuvres with coordination, skill, and speed almost similar to that of an able-bodied person. Performance on reaching and grasping tasks consistently improved during the 34 training

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