This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
The characteristic EEG feature of absence seizures: 
Select and explain. 
A. 3 Hz spike & wave, B. 1-2 Hz spike & wave, C. Generalized polyspikes, D. Hypsarrythmia
A: 3 Hz spike & wave
Answer: A: 3 Hz spike & wave 
Explanation: The electrophysiologic hallmark of typical absence seizures is a generalized, symmetric, 3-Hz spike-and-wave discharge that begins and ends suddenly, superimposed on a normal EEG background. Hypsarrhythmia is an abnormal pattern, consisting of high amplitude and irregular waves and spikes in a background of chaotic and disorganized activity seen on EEG, and frequently encountered in infantile spasms. Ref: Harrisons principles of internal medicine, 18th edition, Chapter 159