Lab rats generally don’t live pleasant lives. Some are infected with diseases. Some are exposed to radiation. Some are sucked nearly dry with ticks. But occasionally a rat makes it lucky and is chosen to participate in a study on pleasure and rewards, where the pleasure and rewards are sex.  

You might think, as I once did, that initiating rat sex would be straightforward.  Male rat + female rat = GO! And… mission complete!

But no. We were wrong, you and I. Even rat sex is not left to chance in a well-designed study. Because who knows? The lady might be tired,or hungry, or stressed, or just not in the mood, or she may not find him to be a suitable reproductive partner.  

Apparently, to make sure that the male rats don’t experience any negative emotion as a result of being rebuffed by potential partners, the researchers don’t just provide able-bodied females,  they “prepare sexually receptive” female rats.  It turns out that depending on the stage of the rat’s ovulatory cycle, which reboots about every 5 days, she may be more or less receptive to sex. To eliminate these extraneous variables, researchers adjust levels of progesterone and/or other   hormones to mimic the rat’s peak estrus. In other words, the females aren’t just sexually mature, they’re horny.  Just imagine for a second if the average human male had such power at his discretion.


But not all rats, even in a pleasure study, can be so lucky.  Researchers need controls. Enter “sham sex.”

What if the male rats derived pleasure, not (just) from the sex, but simply from sexually receptive female rat company?  (I visualize it as the rat equivalent of an old couple sitting in the living room with a good book.)  How do the researchers control for this?  They place sexually receptive females within the male enclosure, but the females are in smaller cages that do not allow the males to copulate.  Not surprisingly,this “sham sex” usually increases signs of stress in the males .

But what about female rats?  Don’t they enjoy sex as well? I noticed digging around the literature that while female rats are studied to provide insights into female-specific reproduction, sexual disjunction, and mothering questions,  male rats tend to be used in general pleasure studies, and the results are often extrapolated to the entire population.  Hmmm.