 Schultz W 2001 Reward signaling by dopamine neurons. Neuroscientist 7:293-302 Thut G, Schultz W, Roelcke U, Nienhusmeier M, Missimer J, Maguire RP, Leenders KL 1997 Activation of the human brain by monetary reward. NeuroReport 8: 1225-8 