Researchers paying really, really close attention to mice having sex have discovered that males make high-pitched squeals during sexual interactions with females. What’s more, the high-frequency vocalizations tell us something about ourselves.

The mouse calls are inaudible to the human ear; only microphones and computers can measure them. Not unlike the songs of birds, mice chirp in definite syllables and structure when having sex, and not unlike your neighbors, the varying patterns in squeaks correspond to definite emotional responses.

In the courtship phase, before mounting the female, male mice emit whistles indicative of approach behavior; after mounting, however, the males’ vocalizations increase in relation to the intensity of the sex. When scientists removed certain single-cell genes of the mice (in particular those related to dopamine and acetylcholine, both of which are tied to emotional expression in humans), the calls changed in volume and duration.

This represents something of a missing puzzle piece for scientists, who have been unable to pinpoint which genes are most crucial in controlling complex emotions and behaviors in humans.

And that’s not all: The researchers found that low doses of amphetamine, the street drug known as speed that activates the brain’s dopamine system, also induce chirps -- indicating that sex and drugs might be more intertwined than we’d imagined in college.

The team of researchers included Haoran Wang, John Yeomans and Shuyin Liang at the University of Toronto, and Jeffrey Burgdorf at Northwestern University in Chicago. The group is hopeful their findings will help in developing drugs to better control emotions, drug abuse, and mood disorders.