MEN automatically fall asleep after having sex because their brains are programmed to shut down, scientists claim.
Researchers from the French government took scans of men’s brains during and after sex to monitor changes in their mental activity.
They found the cerebral cortex, which governs conscious thought, switched off during orgasm.
Two other areas – the cingulate cortex and the amygdala – then sent a message to the rest of the brain telling it to remove all sexual desire, via the release of sleep-inducing chemicals, including serotonin and opioids.
Serge Stoléru, one of the scientists who conducted the research, said: "These experiments give us the first hints as to what happens in the brain during orgasm.”
The findings may provide men with a helpful excuse to turn off the light and go to sleep, but they are unlikely to be welcomed by their partners who do not experience the same effect.
Dr Stoléru explained: "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.”
A recent study also suggested men think about sex 19 times a day.
This confounds the long-held stereotype that men think about sex every seven seconds while awake, amounting to 8000 times over an average 16-hour day.
However, US scientists discovered that, on average, men still think about sex twice as much as women, who entertain the thought just 10 times a day. Women also thought less about food and sleep daily, thinking about them just 15 and 8.5 times respectively.
They put the new numbers down to previous studies, which they say were headline-grabbing but poorly set-up.
The researchers say that in those studies volunteers were often asked to make a guess at how often they thought about sex rather than actually recording it, with the results wrongly influencing men and women for years after.
The team, from Ohio State University, recruited 160 women and 120 men aged 18 to 25 to monitor their thoughts.
In the group, 59 were randomly assigned to count how often they thought about food, 61 sleep and 163 sex. – The Telegraph