The dopamine hypothesis posits that schizophrenia is linked to irregularities in the dopamine system. The original theory suggested that the disorder was caused by a general excess of dopamine or an overabundance of dopamine receptors. However, this view has been refined. More recent research indicates that dopamine abnormalities are specific to different brain regions. An oversupply of dopamine in the limbic system is thought to be responsible for positive symptoms like hallucinations and delusions, while a deficit of dopamine in the prefrontal cortex is associated with negative symptoms such as avolition and alogia.

The Dopamine Hypothesis of Schizophrenia

- Set of dopaminergic axons from the midbrain (VTA) to the limbic
system and cortex 
- Important in reward and reinforcement, especially via the dopamine 2 (D2) receptor - Abnormalities in this pathway are associated with some symptoms of schizophrenia

Rutgers University

- Monoamine transmitter
- Subtypes of dopamine (DA) include D1, D2, D3, D4, and D5 (numbered in the order of their discovery)
- Found in the midbrain and basal forebrain
- Two main dopaminergic neuron pathways include the mesostriatal
pathway and the mesolimbocortical pathway

Dopamine Neurotransmitter 

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

- Set of dopaminergic axons from the midbrain (specifically the substantia nigra) to the basal ganglia (striatum) 
- Has a crucial role in motor control 
- Significant loss of dopamine neurons in this pathway produces movement problems in Parkinson’s disease 

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