1. Department of Neurosurgery, Carver College of Medicine, The University of Iowa, Iowa City, Iowa;
2. Department of Physical Therapy and Rehabilitation Science, Carver College of Medicine, The University of Iowa, Iowa City, Iowa;
3. Department of Bioengineering, The University of Iowa, Iowa City, Iowa;
4. Department of Neurological Surgery, Feinberg School of Medicine, Northwestern University, Chicago, Illinois;
5. Department of Veterans Affairs, VA Medical Center, Iowa City, Iowa