Decisions about sex activate different brain regions in adolescent girls

In a first-of-its-kind study, Indiana University researchers have shown that teenage girls use different parts of their brain when making hypothetical low- and high-risk decisions about sex.

In a pilot study reported in the Journal of Adolescent Health, researchers Devon J. Hensel, Ph.D., and Tom Hummer, Ph.D., analyzed the brain activity and self-reported behaviors of 14- and 15-year-old girls using a functional magnetic resonance image and 30 days of daily diary reports.

Recent studies have demonstrated the advantages of using functional MRI to understand how reward- and control-related regions of the brain are related to different risk behaviors, such as reckless driving or substance use, in adolescence. This is the first study to use functional MRI to link brain activity in mid-adolescent-aged females to their sexual decisions.

The researchers found that teenaged girls spend less time making decisions about participating in risky behavior than they do when evaluating low-risk activities. They also determined that an area of the brain involved with controlling impulses and emotion is more engaged with high- risk sexual decision-making than with other high-risk decisions.

"Learning to express and manage sexuality is a normal part of development," said Dr. Hensel, who is an assistant research professor of pediatrics in the Section of Adolescent Medicine at the IU School of Medicine and an assistant professor of sociology at Indiana University-Purdue University Indianapolis. "During adolescence, young women encounter a variety of new experiences that involve balancing new relationships, heightened emotions and sexual desire. The majority of young women navigate this process without issue, but risky sexual behaviors can be associated with adverse outcomes such as unintended pregnancy and sexually transmitted infections."

"By evaluating brain activity while young people make decisions about high- and low-risk behavior, we can better determine how the brain is involved in managing the emotions and motivations associated with different sex-related behaviors," said Dr. Hummer, assistant research professor in the IU School of Medicine Department of Psychiatry. "Greater knowledge in this area could lead to opportunities to better educate teens about making healthy decisions."

The 14 study participants first underwent functional MRI, a neuroimaging procedure that measures brain activity by detecting changes in blood flow within the areas of the brain. During that procedure, participants were introduced to sex-related and non-sex-related scenarios, and they were asked to rate their likelihood of participating in the low- or high-risk activity. The functional MRI captured the teens' brain activity while they were contemplating the decision.

During sex-related decisions, young women were shown photos of attractive, similarly aged young men. They were also provided information on how many previous sexual partners the young man had, and whether he used a condom the last time he had sex. Presented with low- and high-risk combinations of this information, the young woman rated how likely she would be to have sex with the young man.

During non-sex-related decisions, young women were shown pictures of food, with calorie content described, as well as household items, with details about prices and return policies. Presented with low- and high-risk combinations of this information, the young woman rated the likelihood that she would either eat the food or buy the household item in the pictures.

Researchers found that the anterior cingulate cortex showed greater activation when participants were making decisions about high-risk sex, as compared to high-risk food or item purchases. The anterior cingulate cortex is involved in reward-related decision-making, including controlling emotions and impulses in order to make rational cognitive decisions.

"These results suggest that when a high level of sexual risk is perceived, the brain's resources are directed at controlling emotion and the reward associated with the decision," Dr. Hensel said.

The researchers also noted that greater activity occurred in visual clusters of the brain for low-risk sex decisions as compared to low-risk food- or household-item-related decisions. The visual clusters activated include the occipital cortex, which is involved in general visual processing, and the fusiform gyrus, which is more specifically involved with face recognition and perception of emotions based on facial characteristics. This finding suggests that attractiveness weighed more heavily in the low-risk decision-making process and was less a factor when the boy was determined to be a high-risk potential partner.

"Our findings suggest that low-risk sexual decisions engaged more visual areas of the brain than high-risk decisions, indicating that the visual information was utilized more in making those decisions," Dr. Hummer said.

Young women also provided details about their past sexual attitudes and experiences with 30 days of daily diary reports. Researchers found that participants who reported engaging in any sex in the month before the study rated their likelihood of participating in the high-risk sexual scenario higher than participants who did not report any sexual activity before the study.

In addition, participants who rated their participation in high-risk sexual scenario as more likely reported higher average levels of sexual interest in the month following the functional MRI portion of the study as compared to participants who rated their participation in a high-risk sexual scenario as less likely.

Moreover, participants who rated their participation in the low-risk sexual scenarios as more likely had greater reports of sexual behavior in the month following the functional MRI portion of the study as compared to participants who rated their participation in the low-risk sexual scenario as less likely.

"We were able to demonstrate differences in neural activity between high- and low-risk decisions, including novel findings about how sex-related decisions differ from other types of decisions," Dr. Hensel said. "We also demonstrated that a young woman's response ratings to sexual decisions were linked to her demographic and sexual history, as well as to her daily self-reports of sexual emotions and behaviors following the functional MRI scan.

"This information will help us develop larger, long-term studies to understand how brain function and sexual decision making develop together over time," Dr. Hummer said. "Given the importance of this time frame to young women's learning to have healthy relationship experiences, this research will help us develop targeted health promotion designed to build young women's skills in negotiating these relationships."

Other IU researchers involved in this study are J. Dennis Fortenberry, M.D., M.S.; Lindsay R. Acrurio, Ph.D.; and Thomas W. James, Ph.D.

This research was funded with support from the Indiana Clinical and Translational Sciences Institute, in part by grant number UL1TR001108.