Which neurotransmitter influences movement, learning, and attention; overactivity linked to schizophrenia, undersupply linked to Parkinson's disease?

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Dopamine helps regulate movement, learning, and attention, and its signaling imbalance is tied to both Parkinson's disease and schizophrenia. In Parkinson's disease, there is a loss of dopamine-producing neurons in the substantia nigra, which reduces dopamine in the nigrostriatal pathway and leads to motor symptoms like tremors and rigidity. In schizophrenia, too much dopamine activity in the mesolimbic pathway is linked to positive symptoms such as hallucinations and delusions, while reduced dopamine in the prefrontal cortex (the mesocortical pathway) can contribute to impairments in attention, motivation, and executive function. This combination of motor effects with learning and attention-related changes aligns most closely with dopamine. Other neurotransmitters—norepinephrine for arousal, serotonin for mood, and acetylcholine for memory and muscle activity—do not fit the same pattern of movement impairment coupled with schizophrenia symptoms as cleanly.