A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 20-year-old male is brought to a psychiatrist by his parents for bizarre behavior. His parents report that over the past two semesters in school, his personality and behavior have changed noticeably. He refuses to leave his room because he believes people are spying on him. He hears voices that are persecutory and is convinced that people at school have chips implanted in their brains to spy on him. Screenings for depression and mania are negative. His past medical history is unremarkable. His family history is notable for a maternal uncle with bipolar disorder. He does not drink alcohol or smoke. His temperature is 98.8°F (37.1°C), blood pressure is 115/70 mmHg, pulse is 85/min, and respirations are 18/min. On examination, he appears to be responding to internal stimuli. Which of the following pathways is primarily responsible for these symptoms?
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A
Mesolimbic pathwayCorrect. Mesolimbic dopamine hyperactivity produces the positive symptoms of schizophrenia (delusions, hallucinations); antipsychotics target this pathway therapeutically.
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B
Nigrostriatal pathwayIncorrect. Nigrostriatal dopamine pathway involvement (and its blockade) causes movement side effects (parkinsonism, tardive dyskinesia), not the primary symptoms of schizophrenia.
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C
Tuberoinfundibular pathwayIncorrect. Tuberoinfundibular dopamine pathway involvement (blockade) causes hyperprolactinemia, not psychosis.
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D
Papez circuitIncorrect. The Papez circuit underlies emotional/memory processing — not the dopaminergic mechanism of psychotic symptoms.
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E
Mesocortical pathwayIncorrect. Decreased mesocortical dopamine activity is implicated in the negative and cognitive symptoms of schizophrenia (apathy, flat affect, executive dysfunction), but the patient's prominent positive symptoms (delusions, hallucinations) localize primarily to mesolimbic hyperactivity.
↑ Tap an answer to reveal the reasoning
Answer: A. A 20-year-old male with declining function over two semesters, persecutory delusions (people are spying on him, chips implanted in others' brains), auditory hallucinations, and apparent response to internal stimuli has schizophrenia. The age of onset (late teens to early adulthood, often slightly later in women), family history of psychotic disorder, and absence of mood symptoms support the diagnosis. Positive symptoms (delusions, hallucinations, disorganized thought/behavior) are the hallmark of acute psychosis.
The positive symptoms of schizophrenia are thought to result from hyperactive dopamine signaling in the MESOLIMBIC pathway (projects from the ventral tegmental area to the nucleus accumbens and limbic system). Excess mesolimbic dopamine drives the psychotic symptoms; antipsychotics block D2 receptors in this pathway to reduce positive symptoms. The mesocortical pathway (VTA to prefrontal cortex) is associated with negative and cognitive symptoms via UNDERactivity (paradoxical hypofunction).
Other pathways: nigrostriatal — blockade causes extrapyramidal symptoms (parkinsonism, tardive dyskinesia, acute dystonia); tuberoinfundibular — blockade causes hyperprolactinemia (gynecomastia, galactorrhea, amenorrhea). The Papez circuit involves emotional processing and memory but isn't the mechanism for psychosis.
**Why each option:**
**A.** Correct. Mesolimbic dopamine hyperactivity produces the positive symptoms of schizophrenia (delusions, hallucinations); antipsychotics target this pathway therapeutically.
**B.** Nigrostriatal dopamine pathway involvement (and its blockade) causes movement side effects (parkinsonism, tardive dyskinesia), not the primary symptoms of schizophrenia.
**C.** Tuberoinfundibular dopamine pathway involvement (blockade) causes hyperprolactinemia, not psychosis.
**D.** The Papez circuit underlies emotional/memory processing — not the dopaminergic mechanism of psychotic symptoms.