1. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
2. Department of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
3. Department of Neurology and Rehabilitation Medicine, University of Cincinnati College of Medicine, Cincinnati, OH, USA.
4. Philips Research North America, Cambridge, MA, USA.
5. Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.