David L. Clark is Associate Professor Emeritus, Division of Anatomy, The Ohio State University, Ohio, USA. Nashaat N. Boutros is Professor of Psychiatry and Neurology and Associate-Chair for Research, Wayne State University, Detroit, USA. Mario F. Mendez is Director, Neurobehaviour Unit, Greater Los Angeles Healthcare System and Professor of Neurology and Psychiatry, David Geffen School of Medicine, University of California, Los Angeles, USA.