LIBRARIES A Role for Dopamine Neuron NMDA Receptors in Learning

Midbrain dopamine has demonstrated roles in locomotion, motivation, associative learning, habit formation, action selection and cognition. The many functions of dopamine can be attributed to the multiple projection targets of midbrain dopamin-ergic nuclei and to the multiple characteristic modes of dopamine neuron firing, tonic and phasic. Phasic transients of midbrain dopamine neurons are widely reported to signal errors conveying discrepancies between predicted and actual reward. Knock-ing out NMDARs in dopamine neurons has been shown to attenuate dopaminergic phasic firing providing a potential model for delineating the functions of tonic and phasic dopamine. In order to study the role of dopamine neuron NMDARs in reward-contingent learning, we developed an auditory-cued binary choice task using complex auditory stimuli that lend themselves to efficient learning as well as morphing. We report that mice lacking NMDARs in dopamine neurons have a deficit in learning an auditory two-alternative choice task, in the absence of changes in response vigor. Dopamine neurons respond phasically to rewards as well as reward predictive cues