[1] Johns Hopkins Univ, Appl Phys Lab, Res & Exploratory Dev Dept, Laurel, MD 20707 USA
[2] Univ Louisville, Dept Neurol Surg, Kentucky Spinal Cord Res Ctr, Louisville, KY 40292 USA
[3] Kessler Med Rehabil Res & Educ Corp, West Orange, NJ USA
[4] Medtronic Inc, Minneapolis, MN USA