This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Sleep Disorders, Subject name: Psychiatry
Sawtooth waves are most characteristic of what sleep stage? 
Select and explain. 
A. Stage 1, B. Stage 2, C. Stages 3 and 4, D. REM sleep
D: REM sleep
Answer: D: REM sleep 
Explanation: Sawtooth waves are primarily seen in REM sleep Sleep spindles and K-complexes are seen in stage 2 Delta waves are in deep sleep (stage3 and stage 4)