evidence: Schizophrenia is thought to involve excess activity of the neurotransmitter dopamine in the brain. This has bolstered one possible explanation for Toxoplasma’s behavioural effect: the parasite establishes persistent infections by means of microscopic cysts that grow slowly in brain cells. It can increase those cells’ production of dopamine, which could significantly alter their function. Most other suggested mechanisms also rely on the presence of cysts.