Is it necessary to use brain imaging to understand teen girls' sexual decision making?

“It is feasible to recruit and retain a cohort of female participants to perform a functional magnetic resonance imaging [fMRI] task focused on making decisions about sex, on the basis of varying levels of hypothetical sexual risk, and to complete longitudinal prospective diaries following this task. Preliminary evidence suggests that risk level differentially impacts brain activity related to sexual decision making in these women [i.e., girls aged 14-15 yrs], which may be related to past and future sexual behaviors.”

-Hensel et al. (2015)

Can the brain activity of adolescents predict whether they are likely to make risky sexual decisions in the future?  I think this is the goal of a new pilot study by researchers at Indiana University and the Kinsey Institute (Hensel et al., 2015). While I have no reason to doubt the good intentions of the project, certain aspects of it make me uncomfortable.

But first, I have a confession to make. I'm not an expert in adolescent sexual health like first author Dr. Devon Hensel. Nor do I know much about pediatrics, adolescent medicine, health risk behaviors, sexually transmitted diseases, or the epidemiology of risk, like senior author Dr. J. Dennis Fortenberry (who has over 300 publications on these topics).  His papers include titles such as Time from first intercourse to first sexually transmitted infection diagnosis among adolescent women and Sexual learning, sexual experience, and healthy adolescent sex. Clearly, these are very important topics with serious personal and public health implications. But are fMRI studies of a potentially vulnerable population the best way to address these societal problems?

The study recruited 14 adolescent girls (mean age = 14.7 yrs) from health clinics in lower- to middle-income neighborhoods. Most of the participants (12 of the 14) were African-American, most did not drink or do drugs, and most had not yet engaged in sexual activity.  However, the clinics served areas with “high rates of early childbearing and sexually transmitted infection” so the implication is that these young women are at greater risk of poor outcomes than those who live in different neighborhoods.

Detailed sexual histories were obtained from the girls upon enrollment (see below). They also kept a diary of sexual thoughts and behaviors for 30 days.

Given the sensitive nature of the information revealed by minors, it's especially important to outline the informed consent procedures and the precautions taken to protect privacy. Yes, a parent or guardian gave their approval, and the girls completed informed consent documents that were approved by the local IRB. But I wanted to see more about this in the Methods. For example, did the parent or guardian have access to their daughters' answers and/or diaries, or was that private? This could have influenced the willingness of the girls to disclose potentially embarrassing behavior or “verboten” activities (prohibited by parental mores, church teachings, legal age of consent,¹ etc.). 

I don't know, maybe the standard procedures are obvious to those within the field of sexual health behavior, but they weren't to me.

Turning to more familiar territory, the experimental design for the neuroimaging study involved presentation of four different types of stimuli: (1) faces of adolescent males; (2) alcoholic beverages; (3) restaurant food; (4) household items (e.g., frying pan). My made-up examples of the stimuli are shown below.

Each picture was presented with information that indicated the item's risk level (“high” or “low”):

• Adolescent male faces: number of previous sexual partners and typical condom use (yes/no)
• Alcoholic beverages: number of alcohol units and whether there was a designated driver (yes/no)
• Food: calorie content and whether the restaurant serving the food had been cited in the past year for health code violations (yes/no)
• Household items: whether the object could be returned to the store (yes/no)

For each picture, participants rated how likely they were to: (1) have sex with the male, (2) drink the beverage, (3) eat the food, or (4) purchase the product (1 = very unlikely to 4 = very likely). There were 35 exemplars of each category, and each stimulus was presented in both “high” and “low” risk contexts. So oddly, the pizza was 100 calories and from a clean restaurant on one trial, compared to 1,000 calories and from a roach-infested dump on another trial.

The faces task was adapted from a study in adult women (Rupp et al., 2009) where the participants gave a mean likelihood rating of 2.45 for sex with low risk men vs. 1.41 for high risk men (significantly less likely for the latter). The teen girls showed the opposite result: 2.85 for low risk teen boys vs. 3.85 for high risk teen boys (significantly more likely) — the “bad boy” effect?

But the actual values were quite confusing. At one point the authors say they omitted the alcohol condition: “The present study focused on the legal behaviors (e.g., sexual behavior, buying item, and eating food) in which adolescents could participate.”

But in the Fig. 1 legend, they say the opposite (that the alcohol condition was included):

Panel (A) provides the average likelihood of young women's endorsing low- and high-risk decisions in the boy, alcohol, food, and household item (control) stimulus categories.

Then they say that the low-risk male faces were rated as the most unlikely (i.e., least preferred) of all stimuli.  But Fig. 1 itself shows that the low-risk food stimuli were rated as the most unlikely...

Regardless of the precise ratings, the young women were more drawn to all stimuli when they were in the high risk condition. The authors tried to make a case for more "risky" sexual choices among participants with higher levels of overt or covert sexual reporting, but the numbers were either impossibly low (for behavior) or thought-crimes only (for dreams/fantasy). So it's really hard to see how brain activity of any sort could be diagnostic of actual behavior at this point in their lives.

And the neuroimaging results were confusing as well. First, the less desirable low-risk stimuli elicited greater responses in cognitive and emotional control regions:

Neural activity in a cognitive-affective network, including prefrontal and anterior cingulate (ACC) regions, was significantly greater during low-risk decisions.

But then, we see that the more desirable high-risk sexual stimuli elicited greater responses in cognitive/emotional control regions:

Compared with other decisions, high-risk sexual decisions elicited greater activity in the anterior cingulate, and low-risk sexual decision elicited greater activity in regions of the visual cortex. 

This pattern went in the opposite direction from what was seen in adult women (Rupp et al., 2009), and it implicated a different region of the ACC. It's difficult to draw comparisons, though, because the adult and adolescent groups diverged in age, demographic characteristics, and sexual experience.

Figure adapted from Hensel et al., 2015 (left) and Rupp et al., 2009 (right).


So is it feasible to use fMRI to understand teen girls' sexual decision making? Maybe, from the point of view of logistics and subject compliance, which is no mean feat. But is it necessary, or even informative? Certainly not, in my view. It's not clear what neuroimaging will add to the picture, beyond the participants' fully disclosed sexual histories. Finally, is it ethical to use brain imaging to understand teen girls' sexual decision making? While the future predictive value of the fMRI data is uncertain, linking a biomarker to sensitive sexual information requires extra protection, especially when from a potentially vulnerable adolescent population.


Footnote

¹ In the state of Indiana, it is illegal for an individual 18 years of age or older to have sex with one of the participants in the present study. So if a young women engaged in sexual activity with an 18 year old senior, he could potentially go to jail. Not that this was necessarily the case for anyone here.


References

Hensel, D., Hummer, T., Acrurio, L., James, T., & Fortenberry, J. (2015). Feasibility of Functional Neuroimaging to Understand Adolescent Women's Sexual Decision Making. Journal of Adolescent Health. DOI: 10.1016/j.jadohealth.2014.11.004

Rupp, H., James, T., Ketterson, E., Sengelaub, D., Janssen, E., & Heiman, J. (2009). The role of the anterior cingulate cortex in women's sexual decision making. Neuroscience Letters, 449 (1), 42-47 DOI: 10.1016/j.neulet.2008.10.083