Figure 1.

Reinforcement learning model. In the reinforcement learning model (from Frank et al., 2004), phasic increases in dopamine promote action selection in the thalamus via the D1-receptor “Go” pathway, whereas phasic decreases promote action avoidance via the D2-receptor “NoGo” pathway. Both processes originate in the striatum and receive cortical and subcortical inputs. SNc, substantia nigra pars compacta; GPi, internal segment of the globus pallidus; GPe, external segment of the globus pallidus; SNr, substantia nigra pars reticula.