Regarding the dopamine hypothesis of schizophrenia, which mesolimbic and mesocortical pathway imbalance BEST explains the co-existence of positive and negative symptoms?

• A Hypoactivity of mesolimbic pathway causes positive symptoms; hyperactivity of mesocortical pathway causes negative symptoms
• B Hyperactivity of mesolimbic pathway causes positive symptoms; hypoactivity of mesocortical pathway causes negative symptoms ✓
• C Hyperactivity of both pathways causes all symptoms
• D Hypoactivity of nigrostriatal pathway causes positive symptoms

Explanation

The revised dopamine hypothesis posits that mesolimbic dopamine hyperactivity underlies positive symptoms (hallucinations, delusions) while mesocortical dopamine hypoactivity to the prefrontal cortex underlies negative and cognitive symptoms (alogia, avolition, cognitive deficits). Nigrostriatal hypoactivity is associated with extrapyramidal side effects of antipsychotics, not primary schizophrenia symptoms. This dual-pathway model explains why first-generation antipsychotics effectively treat positive symptoms but worsen negative symptoms and cause EPS.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

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