The anatomical/neurochemical circuits have been conceptualized by current theories of physiology and pathophysiology, into direct, indirect and hyper-direct pathways (17-19). The direct pathway includes the striatum to the GPi to the VL thalamus, and finally to the motor cortex (MC) and supplementary motor area (SMA). The indirect pathway includes the striatum to the GPe to the STN, the stria-tum to the GPi to the VL thalamus, and then to the MC and SMA. The hyper-direct pathway involves projections from the cortex to the STN, to the GPi, to the VL, and then to the MC. Connections from the GPe to the GPi (9) and from the VL thalamus to the putamen (20) have now been recognized. SNpc dopamine neurons are excitatory on striatal neurons in the indirect pathway and inhibitory on striatal neurons in the direct pathway.
Was this article helpful?