Adding to recent controversies surrounding various forms of birth control, a new study out of UCLA suggests that the birth control pill may thin areas in a woman's brain and affect their function.

Published in April in the journal "Human Brain Mapping," the study measured cortical thickness in the brains of 90 women – 44 of whom were using oral contraceptives, and 46 of whom were naturally cycling.

Only women using the combination form of oral contraceptives were used in the study – it did not measure women using progesterone-only or other forms of oral contraceptives. The research found that oral contraceptive use was significantly associated with a thinning in two areas of the brain: the lateral orbitofrontal cortex and the posterior cingulate cortex.

The lateral orbitofrontal cortex is involved in emotion regulation and response to rewards, while the posterior cigulate cortex regulates inward-directed thought, such as recalling personal memories or planning for the future.

Although the study only measured brain structure, the findings suggest that there could be possible effects on behavior.  

"Some women experience negative emotional side effects from taking oral contraceptive pills, although the scientific findings investigating that have been mixed," Nicole Petersen, a neuroscientist at UCLA and the study's lead author, told The Huffington Post. "So it's possible that this change in the lateral orbitofrontal cortex may be related to the emotional changes that some women experience when using birth control pills."

Because the study is one of the first of its kind, as far as measuring effects of the birth control pill on brain structure, it's difficult for scientists to draw any definite conclusions at this point.

But Larry Cahill, a professor of neurobiology and behavior at the University of California-Irvine and a co-author of the study, said while the interest in the link between sex hormones and brain structure has increased in the past few years, he's amazed at the lack of research considering how long the pill has been on the market.

"You might think after 50 years and hundreds of millions of women taking various incarnations of the pill, there would be a large and cohesive and impressive body of evidence on it, but there's next to nothing," Cahill told CNA. "I honestly find that amazing."

Although Cahill cautioned against a panic or alarm because of the recent study, he said it raises further questions for research that are important to the millions of women who use oral contraceptives every day. For example, follow-up studies are needed to determine whether the thinning effect is permanent, or whether it just occurs if a woman is currently using the pill.

In April 2011, Cahill and three other researchers found that the emotional memory of women using hormonal contraception was more similar to that of men than of women. Combined with the evidence of the most recent study, Cahill said one group that might benefit from the pill's possible impact on emotional memory could be women in combat or other traumatic situations. If using hormonal contraception, these women could be potentially less likely to develop post-traumatic stress disorder than naturally cycling women in similar situations, though more research is needed.

These studies are part of a growing body of research on sex differences in the brain, which is challenging the long-held assumption that men and women are mostly biologically the same, save for their reproductive organs, Cahill noted.

"We're all blinded by our assumptions, and there's simply been an assumption…that any differences between (men and women) occur in the bikini zone and that's it," Dr. Cahill said. "And now we're realizing, well, no. There's sex differences all over the place. It's important that we stop assuming that women are just men with pesky hormones."

Challenging assumptions has been somewhat of a road block for Cahill and fellow researchers trying to publish their findings, because they are often dismissed as being "alarmist," Cahill said. However, as a scientist, Cahill said he believes it's important to continue to study the potentially good, bad or neutral effects of a medication that millions of women use for large portions of their life.

"If I'm a woman on the pill, or I know a woman who's on the pill…or I have a daughter who wants to go on the pill, you want to operate from knowledge, not from complete lack of knowledge," he said.

"That was the goal, to explore what the pill might be doing just as we've been doing for 3 or 4 years."