NSW doctor says males have morning erection due to activation of certain brain areas

Besides the brain releasing less of the hormone noradrenaline which causes morning erection in males, the event happens when there is Rapid Eye Movement (REM) during sleep. It is the phase when people dream which also activates certain parts of the brain.

In an article for The Conversation, Sergio Diez Alvarez, director of medicine at the University of Newcastle in Australia, says the boner explains a lot about sexual function. He identifies the areas activated during REM are those that are responsible for stimulating the parasympathetic nerves, suppressing the sympathetic nerves and producing serotonin which are dampened, Daily Mail reports.

During REM, there is movement from sympathetic stimulation to parasympathetic stimulation which do not occur during other parts of sleep. The shift in balance causes the parasympathetic nerve to respond which results in erection.

However, Alvarez says some men experience erection while sleeping even during non-REM sleep, especially older men. But he does not have an explanation for it yet.

Most of the time, people wake up coming out of REM sleep which explains why the penis is erect in the morning. Alvarez adds that because testosterone is at its highest level in the morning, in enhances the frequency of nocturnal erections.

Because there are several sleep cycles every night, men could experience up to five erections at night which lasts 20 to 30 minutes. However, it depends on sleep quality which explains why it may not occur every day in some men.

While the frequency and quality of erections decline gradually as men age, nocturnal erections often happen even when some males are no longer sexually active. There is a similar phenomenon in women when pulses of blood flow in the vagina also during REM sleep. The result is the clitoris is engorged and there is increased vaginal sensitivity along with fluidity, Alvarez writes in The Conversation.