Why men don't want to chat after sex?
Men really do need to sleep after sex because the male brain is designed to switch off at that point, scientists claim.
They scanned men's brains before and during orgasm, and found that the cerebral cortex - or "thinking" area - shuts down, the Daily Mail reported Monday.
Straight afterwards, two other areas, the cingulate cortex and amygdala, tell the rest of the brain to deactivate from sexual desire.
This is accompanied by a surge of chemicals such as oxytocin and serotonin, which can have a powerful sleep-inducing effect, according to the researchers.
Neuroscientist Serge Stoleru, who leads a group at the French medical research council Inserm, said: "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."
Earlier this year, psychologists at the University of Michigan in the US found women whose partners nod off are left feeling insecure and craving affection.