1. Department of Neurosurgery, School of Medicine, Keio University, Tokyo, Japan
2. Department of Neurosurgery, Eiju General Hospital, Tokyo, Japan
3. Department of Neurosurgery, College of Medicine, University of South Florida, Tampa, Florida
4. Department of Neurosurgery, Tokyo-Kita Social Insurance Hospital, Tokyo, Japan
5. Department of Physiology, School of Medicine, Keio University, Tokyo, Japan