A new study finds the use of birth control pills is associated with significantly lower cortical thickness in certain brain structures believed to be important in the response to emotional stimuli.

The study, published by the journal Human Brain Mapping, states that oral contraceptives (OCs) "contain steroid hormones that may affect the brain's structure and function."

Researchers Nicole Petersen, Alexandra Touroutoglou, Joseph Andreano, and Larry Cahill studied 90 women, 44 users of the combination form of oral contraceptives, and 46 non-users, and compared the cortical thickness and volume of various brain regions between the two groups. They found significant thinning in the lateral orbitofrontal cortex and the posterior cingulate cortex in the women on birth control pills.

"These regions are believed to be important for responding to rewards and evaluating internal states/incoming stimuli, respectively," the authors write.

The researchers note that, according to the Centers for Disease Control and Prevention, OCs "are used by the majority of women in the United States for at least one period of time during their reproductive years and are approved by the Food and Drug Administration for pediatric use" after the onset of the first menstrual period, also known as menarche.

"Ample evidence has shown that brain development continues well past the onset of menarche…and that some features of adolescent brain development differ between male and female," they add.

A study published in 2004 at the National Institutes of Health describes what occurs with damage to the orbitofrontal cortex:

Damage to the orbitofrontal cortex can impair the learning and reversal of stimulus-reinforcement associations, and thus the correction of behavioural responses when there are no longer appropriate because previous reinforcement contingencies change. The information which reaches the orbitofrontal cortex for these functions includes information about faces, and damage to the orbitofrontal cortex can impair face (and voice) expression identification. This evidence thus shows that the orbitofrontal cortex is involved in decoding and representing some primary reinforcers such as taste and touch; in learning and reversing associations of visual and other stimuli to these primary reinforcers; and in controlling and correcting reward-related and punishment-related behavior, and thus in emotion.