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Papez circuit — MRCPsych Paper A MCQ

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ModerateNeuroanatomyPapez circuitMRCPsych Paper A

A 46-year-old man has persistent severe anterograde amnesia following Wernicke encephalopathy caused by thiamine deficiency. MRI shows bilateral mammillary-body atrophy. Disruption of which neural pathway best explains his memory impairment?

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Correct answer: A — Hippocampus → fornix → mammillary bodies → mammillothalamic tract → anterior thalamic nucleus

The correct answer is A. The mammillary bodies are diencephalic components of the Papez circuit, receiving hippocampal output through the fornix and projecting through the mammillothalamic tract to the anterior thalamic nuclei. Damage to this memory network contributes to the profound anterograde amnesia of Korsakoff syndrome. Option C is principally involved in emotional and autonomic responses. Option E is a descending motor pathway, so disruption produces upper motor neurone signs. Option D participates in basal-ganglia motor control and is implicated in parkinsonism rather than isolated amnesia. Option B is the visual pathway; lesions cause visual-field defects. Thus the clinical syndrome and mammillary-body localisation specifically indicate disruption of the Papez circuit.

Reference: Pitel AL et al. Temporal Cognitive and Brain Changes in Korsakoff Syndrome. Neurology. 2021. https://pubmed.ncbi.nlm.nih.gov/33637634/