Reward mechanisms in the brain and their role in dependence: evidence from neurophysiological and neuroimaging studies.
This article reviews neuronal activity related to reward processing in primate and human brains. In the primate brain, neurophysiological methods provide a differentiated view of reward processing in a limited number of brain structures. Dopamine neurons respond to unpredictable rewards and produce a global reinforcement signal. Some neurons in the striatum also react to the expectation and detection of reward. Other striatal neurons show reward-related activities related to the preparation, initiation and execution of movement. Orbitofrontal neurons discriminate among different rewards and code reward preferences. In the human brain, regions belonging to a meso-striatal and meso-corticolimbic loop respond to reinforcement stimuli in control subjects. These observations corroborate results obtained in primates. Additionally, reward induces activation in regions specific to task performance. Our results also show a similar pattern of reward-related activation in nicotine and opiate addicts. Thus, in contrast to healthy subjects, typical reward-related regions respond in addicts to monetary reward but not to nonmonetary reinforcement. Reduced activation in performance-related regions is also observed in both groups of dependent subjects. The results of animal and human studies suggest that dopamine and dopamine-related regions are associated with the integration of motivational information and movement execution. Dopamine-related pathological disorders can be associated with movement disorders, such as Parkinson's disease or with false motivational attributions such as drug dependence.
Martin-Soelch
C
C
PET Program, Paul Scherrer Institute, CH-5232, Villigen, Switzerland. chantal.martin@unibas.ch
Leenders
K L
KL
Chevalley
A F
AF
Missimer
J
J
Künig
G
G
Magyar
S
S
Mino
A
A
Schultz
W
W
D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000503:physiopathology; D004298:Dopamine / Q000378:metabolism; D006801:Humans; D009068:Movement / Q000187:drug effects / Q000502:physiology*; D009415:Nerve Net / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000503:physiopathology; D011323:Primates; D011597:Psychomotor Performance / Q000187:drug effects / Q000502:physiology; D012201:Reward; D019966:Substance-Related Disorders / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D014055:Tomography, Emission-Computed
D004298:Dopamine