[1] Keio Univ, Sch Med, Dept Neuropsychiat, Tokyo, Japan
[2] Ctr Addict & Mental Hlth, Geriatr Mental Hlth Program, Toronto, ON, Canada
[3] Keio Univ, Dept Psychol, Tokyo, Japan
[4] Keio Univ, CARLS, Tokyo, Japan
[5] Natl Ctr Neurol & Psychiat, Dept Psychophysiol, Tokyo, Japan
[6] Ctr Addict & Mental Hlth, Res Imaging Ctr, Multimodal Imaging Grp, Toronto, ON, Canada
[7] Univ Toronto, Dept Psychiat, Toronto, ON, Canada
[8] Yokohama City Univ, Sch Med, Dept Physiol, Yokohama, Kanagawa 236, Japan
[9] Albert Einstein Coll Med, Dominick P Purpura Dept Neurosci, New York, NY USA