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Hippocampal amnesia — MRCPsych Paper A MCQ

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ModerateNeuroanatomyHippocampal amnesiaMRCPsych Paper A

A 54-year-old man is assessed 3 months after a cardiac arrest. He repeatedly forgets conversations and events occurring since the arrest and cannot recall a word list after a delay. Attention, digit span, language, executive function and previously learned motor skills are relatively preserved. MRI shows symmetrical medial temporal lobe volume loss, with sparing of the frontal lobes and diencephalon. Bilateral damage to which structure best accounts for this pattern?

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Correct answer: C — Hippocampus

The correct answer is C, the hippocampus. Bilateral hippocampal injury disrupts the encoding and consolidation of new declarative, particularly episodic, memories, producing marked anterograde amnesia despite relatively preserved attention, working memory and procedural skills. The hippocampus is located in the medial temporal lobe and is vulnerable to hypoxic-ischaemic injury. Mammillary-body and mediodorsal-thalamic lesions can cause diencephalic amnesia, classically in Korsakoff syndrome, but the diencephalon is spared here. Dorsolateral prefrontal damage would predominantly impair executive function and working memory. Degeneration of the nucleus basalis of Meynert causes widespread cortical cholinergic dysfunction and a broader cognitive syndrome rather than this selective episodic-memory deficit.

Reference: Yonelinas AP et al. The role of recollection, familiarity, and the hippocampus in episodic and working memory. Neuropsychologia. 2024;193:108777. https://pubmed.ncbi.nlm.nih.gov/15885718/