The basal ganglia are critical for selecting actions and evaluating their 
outcome. Although the circuitry for selection is well understood, how these 
nuclei evaluate the outcome of actions is unknown. Here, we show in lamprey that 
a separate evaluation circuit, which regulates the habenula-projecting globus 
pallidus (GPh) neurons, exists within the basal ganglia. The GPh neurons are 
glutamatergic and can drive the activity of the lateral habenula, which, in 
turn, provides an indirect inhibitory influence on midbrain dopamine neurons. We 
show that GPh neurons receive inhibitory input from the striosomal compartment 
of the striatum. The striosomal input can reduce the excitatory drive to the 
lateral habenula and, consequently, decrease the inhibition onto the 
dopaminergic system. Dopaminergic neurons, in turn, provide feedback that 
inhibits the GPh. In addition, GPh neurons receive direct projections from the 
pallium (cortex in mammals), which can increase the GPh activity to drive the 
lateral habenula to increase the inhibition of the neuromodulatory systems. This 
circuitry, thus, differs markedly from the "direct" and "indirect" pathways that 
regulate the pallidal (e.g., globus pallidus) output nuclei involved in the 
control of motion. Our results show that a distinct reward-evaluation circuit 
exists within the basal ganglia, in parallel to the direct and indirect 
pathways, which select actions. Our results suggest that these circuits are part 
of the fundamental blueprint that all vertebrates use to select actions and 
evaluate their outcome.