1. Department of Rehabilitation Medicine, University of Wisconsin Medical School, Madison, WI 53706 (USA)
2. Department of Physiology, University of New Mexico, Albuquerque, NM 87131 (USA)
3. Department of Orthopedic Surgery, Mayo Graduate School of Medicine, Rochester, MI 55905 (USA)
4. Department of Psychiatry, Arizona Health Sciences Center, Tucson, AZ 85724 (USA)