Striatal dopamine transmission in healthy humans during a passive monetary reward task.

Hakyemez HS, Dagher A, Smith SD, Zald DH
Neuroimage. 2008 39 (4): 2058-65

PMID: 18063390 · DOI:10.1016/j.neuroimage.2007.10.034

Research on dopamine (DA) transmission has emphasized the importance of increased phasic DA cell firing in the presence of unpredictable rewards. Using [(11)C]raclopride PET, we previously reported that DA transmission was both suppressed and enhanced in different regions of the striatum during an unpredictable reward task [Zald, D.H., Boileau, I., El Dearedy, W., Gunn, R., McGlone, F., Dichter, G.S. et al. (2004). Dopamine transmission in the human striatum during monetary reward tasks. J. Neurosci. 24, 4105-4112]. However, it was unclear if reductions in DA release during this task reflected a response to the high proportion of nonrewarding trials, and whether the behavioral demands of the task influenced the observed response. To test these issues, we presented 10 healthy subjects with an automated (passive) roulette wheel game in which the amount of reward and its timing were unpredictable and the rewarding trials greatly outnumbered the nonrewarding ones. As in the previous study, DA transmission in the putamen was significantly suppressed relative to a predictable control condition. A similar suppression occurred when subjects were presented with temporally unpredictable novel pictures and sounds. At present, models of DA functioning during reward do not account for this suppression, but given that it has been observed in two different studies using different reward paradigms, this phenomenon warrants attention. Neither the unpredictable reward nor the novelty conditions produced consistent increases in striatal DA transmission. These data suggest that active behavioral engagement may be necessary to observe robust statewise increases in DA release in the striatum.

MeSH Terms (20)

Acoustic Stimulation Adult Affect Caudate Nucleus Dopamine Dopamine Antagonists Functional Laterality Humans Image Processing, Computer-Assisted Magnetic Resonance Imaging Male Motivation Neostriatum Photic Stimulation Positron-Emission Tomography Putamen Raclopride Radiopharmaceuticals Reward Synaptic Transmission

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