1. Newman Laboratory, Mechanical Engineering Department, Massachusetts Institute of Technology, 77 Massachusetts Ave, office 3-137, Cambridge, MA 02139, USA. E-mail: hikrebs@mit.edu
2. Massachusetts Institute of Technology, Brain and Cognitive Sciences Department
3. Cornell University Medical College, Department Neurology and Neuroscience, Burke Institute of Medical Research
4. Veterans Health Administration, Department of Rehabilitation and Development
5. Burke Rehabilitation Hospital, White Plains, NY, USA