Your male partner can't stay awake after sex? Maybe you should blame it on biology.

At least, that's one of the plausible conclusions of a new study led by Dr. Serge Stoléru, published in the latest copy of Neuroscience & Biobehavioral Reviews.

While the study itself may not be quite as engaging as "50 Shades of Grey," it points out that your pillow talk doesn't have to be, either.

That's because after an orgasm, men tend to experience decreased activity in the prefrontal cortex -- the region of the brain most commonly associated with processing a variety of different information streams and responding appropriately.

Immediately following this reaction, two other brain areas (the cingulate cortex and amygdala) direct him to disengage from sexual thoughts. As this happens, explains the Daily Mail, oxytocin and serotonin flood the brain, which often creates a powerful sleep-inducing one-two punch.

Prolactin, a chemical associated with feeling satiated, also enters the mix. Prior studies, notes Digital Journal, indicate that men who naturally have lower levels of prolactin tend to feel less sleepy after sex.

Don't buy the science? Here's another explanation: "men go to sleep because women don't turn into a pizza," jokes Dave Zinczenko, the author of "Men, Love and Sex: The Complete User Guide For Women."

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