Nocturnal penile tumescence (NPT) is a spontaneous erection of the penis during sleep or when waking up. Along with nocturnal clitoral tumescence, it is also known as sleep-related erection. Colloquially, the term morning wood, or less commonly, morning glory is also used,[1] although this is more commonly used to refer specifically to an erection beginning during sleep and persisting into the period just after waking. Men without physiological erectile dysfunction or severe depression[2] experience nocturnal penile tumescence, usually three to five times during a period of sleep, typically during rapid eye movement sleep.[3] Nocturnal penile tumescence is believed to contribute to penile health.[4]
^Schmidt MH, Schmidt HS (March 2004). "Sleep-related erections: neural mechanisms and clinical significance". Current Neurology and Neuroscience Reports. 4 (2): 170–178. doi:10.1007/s11910-004-0033-5. PMID14984691. S2CID26939007.
^Thase ME, Reynolds CF, Jennings JR, Frank E, Howell JR, Houck PR, et al. (May 1988). "Nocturnal penile tumescence is diminished in depressed men". Biological Psychiatry. 24 (1): 33–46. doi:10.1016/0006-3223(88)90119-9. PMID3370276. S2CID24315629.