2013年2月21日木曜日

Dopamine Encoding of Pavlovian Incentive Stimuli Diminishes with Extended Training


Jeremy J. Clark, Anne L. Collins, Christina Akers Sanford, and Paul E. M. Phillips
The Journal of Neuroscience, 20 February 2013, 33(8):3526-3532; doi:10.1523/JNEUROSCI.5119-12.2013

Dopamine is highly implicated both as a teaching signal in reinforcement learning and in motivating actions to obtain rewards. However, theoretical disconnects remain between the temporal encoding properties of dopamine neurons and the behavioral consequences of its release. Here, we demonstrate in rats that dopamine evoked by pavlovian cues increases during acquisition, but dissociates from stable conditioned appetitive behavior as this signal returns to preconditioning levels with extended training. Experimental manipulation of the statistical parameters of the behavioral paradigm revealed that this attenuation of cue-evoked dopamine release during the postasymptotic period was attributable to acquired knowledge of the temporal structure of the task. In parallel, conditioned behavior became less dopamine dependent after extended training. Thus, the current work demonstrates that as the presentation of reward-predictive stimuli becomes anticipated through the acquisition of task information, there is a shift in the neurobiological substrates that mediate the motivational properties of these incentive stimuli.

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