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English: Figure 1. Dopamine hypersensitivity hypothesis. (a) In short-term administration of dopamine receptor-blocking antipsychotics, upregulation of the indirect pathway occurs: the thalamus is inhibited by excitatory projections (via glutamic acid; red arrows) from the subthalamic nucleus to the internal globus pallidus, leading to inhibition (via GABA, blue arrows) of motor output. (b) Long-term administration of antipsychotics and chronic dopamine D2 receptor blockade leads to downregulation of the indirect pathway; excitatory input to the internal globus pallidus via the subthalamic nucleus is weakened, resulting in increased inhibition of the internal globus pallidus. This in turn weakens the inhibitory projections to the thalamus, and results in overstimulation of motor outputs (i.e. tardive dyskinesia).