The study, published in a forthcoming issue of Pharmacology, Biochemistry and Behavior, shows that moderate doses of caffeine affect sexual behavior in female rats.

Conducted by Fay Guarraci, an assistant professor of psychology at Southwestern University, and Stacey Benson, a 2005 Southwestern graduate, the study suggests that caffeinated beverages such as coffee could affect sexual behavior in humans—albeit possibly only in humans who have never had such beverages before.

Guarraci and Benson gave 108 female rats a moderate dose of caffeine before a mating test to determine if the caffeine had any effect on female mating behavior. They found that administration of caffeine shortened the amount of time it took the females to return to the males after receiving an ejaculation, suggesting that the females were more motivated to be with the male rats.

While it is tempting to speculate that caffeine exposure could also affect sexual motivation in other female mammals such as humans, Guarraci cautioned that may not be the case since most humans consume moderate doses of caffeine on a daily basis.

"These rats had never had caffeine before," she said. "In humans, it might enhance the sexual experience only among people who are not habitual users."

Guarraci said, however, that the study should add to our understanding of the relationship between the brain and behavior.

"Understanding the circuits that control this behavior will help us understand how the brain works and what part of the brain mediates motivation because sexual behavior is a motivative behavior," she said.