1. Department of Physical Medicine and Rehabilitation, Hennepin County Medical Center, Minneapolis, Minnesota.
2. Department of Physical Medicine and Rehabilitation, University of Minnesota, Minneapolis, Minnesota.
3. Department of Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota.
4. Department of Neurosurgery, University of Minnesota, Minneapolis, Minnesota.
5. Division of Neurosurgery, Department of Surgery, Hennepin County Medical Center, Minneapolis, Minnesota.
6. Division of Biostatistics, School of Public Health, University of Minnesota, Minneapolis, Minnesota.