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: Psychiatry
Deep sleep is characterized by 
Select and explain. 
A. α, B. β, C. δ, D. θ
C: δ
Answer: C: δ 
Explanation: Deep sleep or NREM 3 is characterized by presence of δ waves → Frequency 0-4 Hz.
Hence, NREM 3 is also called slow wave sleep.