Fig. 3
From: The onset of motor learning impairments in Parkinson’s disease: a computational investigation
Network structure. Different brain areas are represented in separate layers. Internally, neurons are optionally grouped in columns. Dashed lines indicate plastic connections. The line end represents the influence of a neurotransmitter on the downstream group of neurons: glutamate is excitatory, GABA (gamma-aminobutyric acid) is inhibitory and dopamine is a modulatory neurotransmitter. The process of action selection is expressed by the direct, indirect, and hyperdirect pathways of the BG, modulated by dopamine. The premotor cortex (PMC) selects a response via direct projections from the input gated by BG through the thalamus