It is a constant source of tension between couples — the woman wants to cuddle and chat after sex, but the man just wants to roll over and have a good snooze. Scientists have come with an explanation that could make women understand men better.
According to a new study, the male brain is designed to "switch off" immediately after an orgasm. The study, published in the journal Neuroscience and Biobehavioral Reviews, says that ejaculation is associated with decreased activation throughout the prefrontal cortex.
The scientists conducted neuroimaging scans of men's brains before, during and after orgasm and found that the prefrontal cortex, the area associated with consciousness, alertness and mental activity, simply "switches off" after an orgasm. The process is associated with release of chemicals such as oxytocin and serotonin which have a pronounced sleep-inducing effect.
According to neuroscientist Serge Stoleru, of the French medical research council, Inserm: "These experiments give us the first hints as to what happens in the brain during orgasm. After men have an orgasm they usually experience a refractory period when they cannot be aroused. For women it seems to be different.They don’t seem to have such a strong refractory period and may be asking for more when their partners just want a rest."
One of the chemicals released after orgasm is prolactin, which is linked to the feeling of satiety and relaxation. Previous research found that man who have lower levels of prolactin tend to be less tired after sex. According to Stoleru: "The human brain is involved in all the successive steps of sexual behavior," and according to the study abstract, changes in the brain during and after orgasm help to "understand how... regional brain responses could account for the varied facets of the subjective experience of sexual arousal."
Besides prolactin, the male brain is also flooded with serotonin after sex, another powerful relaxation-inducing brain chemical. The combined effect of prolactin and serotonin in the aftermath of orgasm is that the brain prefrontal cortex switches off almost all sexual desire.
But psychologists have often pointed out that the notorious but characteristic "roll-over effect" in men leaves women who are seeking after-sex display of affection feeling insecure and distressed. The new study finds an excuse for men, saying they just need to rest after sex.
The Daily Mail reports that a 2005 study also found that blood rush after climax depletes glycogen that produces energy in the muscles. Since men, on the average, have significantly higher muscle density than women, they tend to feel more tired after a round of sex.
The Daily Mail also reports a survey of about 10,000 adults by the organizers of The Vitality Show, that found that eighty percent of men say they feel better able to drift off after sex, compared to just 46 percent of women.
Dr. Neil Stanley, of the University of Surrey, concluded: "As frustrating as it is for most women that their male partners just roll over and fall asleep after sex, men aren't entirely to blame. Humans are the only animals in which sleep and sex are linked and while often seen as just a poor excuse, there are scientific reasons why men feel tired after sex."