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Mismatch negativity — MRCPsych Paper A MCQ

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ModerateNeurophysiology and neurochemistryMismatch negativityMRCPsych Paper A

A 24-year-old man with schizophrenia undergoes EEG during a passive auditory oddball task. Repeated standard tones are interspersed with infrequent tones of a different duration. He watches a silent film and is not required to respond to the tones. Compared with healthy controls, the deviant-minus-standard waveform shows an attenuated frontocentral negative deflection approximately 100–250 ms after each deviant tone. Which event-related potential abnormality does this describe?

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Correct answer: D — Reduced mismatch negativity

The correct answer is D, reduced mismatch negativity (MMN). MMN is an early frontocentral event-related potential elicited automatically when an infrequent auditory stimulus differs from repeated standards, even when attention is directed elsewhere. Its amplitude is commonly reduced in schizophrenia, reflecting impaired pre-attentive auditory deviance detection. P50 suppression assesses sensory gating using paired stimuli rather than detection of an oddball tone. N100 is primarily an obligatory response to sound onset and is not specifically the deviant-minus-standard response described. P300 occurs later and generally requires attention to, or active detection of, the target. Contingent negative variation is a slow anticipatory potential arising between a warning stimulus and an expected imperative stimulus.

Reference: Koshiyama D, et al. Reduced Auditory Mismatch Negativity Reflects Impaired Deviance Detection in Schizophrenia. Schizophrenia Bulletin. 2020;46(4):937–946. https://pubmed.ncbi.nlm.nih.gov/32072183/