This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Sleep disorders and eating disorders, Subject name: Psychiatry
How to differentiate between psychological and organic erectile dysfunction 
Select and explain. 
A. Nocturnal penile tumescence, B. PIPE therapy, C. Sildenafil induced erection, D. Squeeze technique
A: Nocturnal penile tumescence
Answer: A: Nocturnal penile tumescence 
Explanation: Psychological impotence usually occurs acutely. The early morning erections and erections during REM sleep (nocturnal penile tumescence; NPT) are usually preserved. If a man repos of spontaneous erections at times when he does not plan to have an intercourse, having morning erections, or having good erections with masturbation or with paners other then his usual one, the organic causes can be considered negligible. Nocturnal penile tumescence is a normal physiological phenomenon seen in males during early morning hours. Squeeze technique is used in pre mature ejacualtion Ref: A Sho Textbook of Psychiatry, Niraj Ahuja, 7th Edition, pg. no. 128, 130 Synopsis of Psychiatry, 11e, pg 577.