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Absence seizure physiology — MRCPsych Paper A MCQ

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ModerateNeurophysiology and neurochemistryAbsence seizure physiologyMRCPsych Paper A

A 10-year-old child has frequent, abrupt episodes of behavioural arrest lasting 5–10 seconds, with immediate recovery and no postictal confusion. EEG during an episode shows generalized, synchronous 3-Hz spike-and-wave discharges. Which neurophysiological mechanism best accounts for this EEG pattern?

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Correct answer: A — Pathological oscillation in reciprocal cortico-thalamo-cortical circuits

The correct answer is A. Brief behavioural arrest, immediate recovery and generalized 3-Hz spike-and-wave discharges identify a typical absence seizure. Its EEG pattern reflects pathological rhythmic synchronization within reciprocal cortico-thalamo-cortical networks. Interactions among cortical neurons, thalamocortical relay neurons and the reticular thalamic nucleus promote rebound burst firing, partly through T-type calcium-channel activity. Recurrent CA3 excitation is more closely associated with focal hippocampal seizure mechanisms and would not explain a generalized 3-Hz pattern. Cortical spreading depolarisation is associated with migraine aura. Reduced reticular activating system output can impair consciousness but does not produce stereotyped spike-and-wave discharges. Postsynaptic nicotinic receptor blockade causes neuromuscular weakness rather than transient behavioural arrest with an ictal EEG abnormality.

Reference: Akman O, Onat F. Absence seizures: Update on signaling mechanisms and networks. Epilepsia Open. 2025. https://pubmed.ncbi.nlm.nih.gov/40522613/