Fig. 2
From: The onset of motor learning impairments in Parkinson’s disease: a computational investigation
Topology connection diagram of the model. The corticostriatal–thalamocortical loop, including the direct, indirect, and hyperdirect pathways of the BG, is represented. The direct pathway-projecting Go neurons in the striatum project directly to the GPi, having the effect of disinhibiting the thalamus and executing a motor response represented in the cortex. The indirect pathway-projecting NoGo neurons have the opposite effect and suppress actions from getting executed. Dopamine from the Substantia Nigra pars compacta (SNc) projects to the striatum, exerting excitation of Go cells via D1 receptors, and inhibition of NoGo cells via D2 receptors. The Subthalamic nucleus (STN) receives excitatory projections from the cortex in the hyperdirect pathway and excites GPi; the external Globus Pallidum (GPe) provides an inhibitory effect on STN activity. Areas not belonging to BG are marked in italic