By: Terry E. Robinson, Department of Psychology University of Michigan
Saturday, December 11, 2010
Our everyday behavior is guided by learned associations we make between salient stimuli in the environment and rewards we consume. For some individuals a Starbuck’s sign is nothing more than a sign (i.e. predictor). For others, the mere sight of the large green circle elicits feelings of craving and desire, causing an irresistible urge to purchase their drink of choice. For individuals in the latter category, the sign can draw them towards it and create a conditioned motivational state consisting of a desire for coffee (i.e., the sign itself acquires incentive value). In a recent study, Flagel and colleagues used rats that differ in how they respond to a cue that predicts a food reward to uncover the neurobiology that regulates learning about rewards.
It has been known for years that the neurotransmitter dopamine plays a critical role in how the brain responds to rewards, but until now the exact nature of its role has not been fully understood. The prevailing view has been that dopamine is especially important for learning what signals in the environment predict reward. In contrast, others have argued that dopamine is important for assigning incentive or motivational value to cues that signal reward. Flagel and colleagues have demonstrated that for rats, like humans, there are large individual differences in how one responds to signs associated with reward. In their experiment all rats learned that presentation of a cue signaled impending reward delivery (tasty food); however, only for a subset of rats did the predictive cue itself become rewarding and a target of motivated behavior. They then asked whether dopamine activity was related to learning per se, or to whether the sign acquired incentive motivational properties. They found that dopamine is not involved in learning about rewards in all individuals, and all situations, but acts selectively in a form of reward learning in which incentive value is assigned to signs that predict rewards. Individuals with a propensity for this form of learning find it especially difficult to resist reward cues, a trait that may be associated with reduced impulse control and addictive behavior. Thus, in addition to redefining the role of dopamine in reward learning, these results provide an important step in understanding and treating impulse-control problems that are prevalent across psychiatric populations.
To read the entire article http://www.lsa.umich.edu/psych/downloads/inthenews/Nature.2010.pdf.