Harold E. Doweiko, Concepts of Chemical Dependency (Belmont, Calif.: Brooks Cole, 2008), 362–82.

K. C. Berridge & M. L. Kringelbach, “Affective Neuroscience of Pleasure: Reward in Humans and Animals”, Psychopharmacology 199 (2008): 457–80; Wolfram Schultz, “Behavioral Theories and the Neurophysiology of Reward”, Annual Review of Psychology 57 (2006): 87–115.