1. San Francisco Veteran's Affairs Medical Center, San Francisco, California.
2. Department of Neurological Surgery, University of California–San Francisco, San Francisco, California.
3. Department of Neurological Surgery, Beijing Tiantan Hospital, Capital Medical University, Beijing, P.R. China.
4. Universitätsklinikum Hamburg-Eppendorf, Hamburg, Germany.
5. Department of Physical Therapy Rehabilitation Science, University of California–San Francisco, San Francisco, California.