The structure of the cortico-basal ganglia-thalamo-cortical loop model.

The BG receives inputs from the prefrontal cortex (PFC) signaling the conditioning stimulus (CS) as well as reward inputs via substantia nigra pars compacta (SNc). The SNc forms a dopamine reward prediction error (RPE) signal, which governs plasticity of the connections from the PFC (DA LTP/LTD; green). The BG input structure, striatum, contains medium spiny neurons (MSNs), which cluster in 2 subtypes: D1 and D2 dopamine receptor-containing (direct and indirect pathways respectively). The rest of the nuclei are the globus pallidus external (GPe), subthalamic nucleus (STN), and the output structures: substantia nigra pars reticulata and globus pallidus internal (SNr/GPi). The loop is completed by connections from and to premotor cortices/thalamus (PMC/Thal). The two channels of the loop are colored purple/blue.