I’m on the road (attending a symposium at MIT: New Insights on Early Life Stress and Mental Health) so this one’s going to be brief. Neural prosthetics are an exciting interface between basic research and technology, an area where the path from fundamental discoveries in the organization and function of the brain to translational advances has been remarkably clear. Cochlear implants have already demonstrated their utility for replacing/enhancing auditory function, and more and more promising advances are coming out all the time in retinal implants. Motor prostheses are another exciting area with the promise to restore motor control to paralyzed individuals and today’s paper by Lee Miller and colleagues represents another step towards a potential prosthetic for spinal injury patients.
The paper describes an advance in functional electrical stimulation (FES), a procedure by which signals from motor cortex are decoded and used to directly stimulate the arm muscles, bypassing the spinal cord. The subjects in this case are monkeys whose arms are temporarily paralyzed by injecting lidocaine into the peripheral nerves. This work follows on from previous work from both this group and others demonstrating the efficacy of FES for simple movements, and extends it to grasping tasks requiring the coordination of multiple muscles. If a picture says a thousand words, I don’t know how many a movie says, but the video clips associated with the paper explain what the animals could and couldn’t do with the FES better than I ever can:
The demonstration is indeed compelling with translational promise, but from an editorial standpoint, these are always interesting papers. As one reviewer once said about neural prosthetic papers (I’m paraphrasing here), you neither have a novel conceptual advance, nor an engineering benchmark to judge them on. Like other translational papers, they fall under a slightly different rulebook, and tend to involve more subjective evaluation than usual. In this case, there was a lot of discussion by the reviewers of how big an achievement the current work represented over the previous FES demonstrations. There was much discussion of whether they had done enough to demonstrate replicability and generality. Bit of trivia: this paper spent the longest time on my desk of any in recent years. The original version was received back in 2009 and was ultimately deemed promising, but too preliminary as the system had only been demonstrated on only one monkey and on one task. We received the next version at the end of last year, and all editors and reviewers were convinced that the extension to two subjects and two tasks made it a technically sound advance. The question of how many subjects we generally require for a study is a discussion for another day (very brief version: we defer to the field for the standards, but in cases where it is appropriate, we consider whether a result merits publication as a proof of principle).
In any case, this study adds to the list of impressive achievements made in recent years in motor prostheses. It’s a prime example of how apparently academic inquiry – basic understanding of the coding and organization of animal motor cortex – is leading to translational advances that are very likely to improve the lives of human patients in the near future. A good example to use when explaining the importance of basic science to the general public.