Figure 2.

Basal ganglia model. A possible model whereby basal ganglia compute the utility of gains and losses via two segregated pathways in the corticostriato-thalamocortical circuit. Striatal output neurons of the direct pathway express D1 receptors and project to the internal globus pallidus (GPi) and the substantia nigra pars reticulata (SNr), and has an action selection effect on cerebral cortex. Striatal output neurons in the indirect pathway express D2 receptors and reduce the tonic inhibition of the external globus pallidus (GPe) on the GPi/SNr, which leads to action inhibition in the cortex. D1 receptors respond mainly to phasic (high concentration) dopamine signaling due to their low affinity for dopamine. D2 receptors have high affinity for dopamine and respond to lower tonic dopamine levels. Excitatory projections in green, inhibitory in red.