ArticlesHigh-performance neuroprosthetic control by an individual with tetraplegia
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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