1. Behavioral Neuroscience Branch, IRP/NIDA/NIH, Baltimore, MD, USA.
2. Center for Social and Affective Neuroscience, Linköping University, Linköping, Sweden.
3. Neuroimaging Research Branch, IRP/NIDA/NIH, Baltimore, MD, USA.
4. School of Pharmacy, University of Camerino, Camerino, Italy.
5. Department of Psychology, University of Maryland College Park, College Park, MD, USA.