1. Department of Physical Medicine and Rehabilitation, Harvard Medical School, Spaulding Rehabilitation Hospital, Massachusetts General Hospital and Boston VA Healthcare System, Boston, MA, USA
2. Department of Neurology, University of North Carolina School of Medicine, Chapel Hill, NC, USA
3. Department of Physical Medicine and Rehabilitation, Neuromuscular Section, University of California, Davis School of Medicine, Sacramento, CA, USA
4. Duke University School of Medicine and Durham Veterans Affairs Medical Center, Durham, NC, USA
5. Department of Physical Medicine and Rehabilitation, St Luke’s Rehabilitation Institute, Spokane, WA, USA