Team measures brain response to visual sexual stimuli

By Rachel Robertson

Why would two Emory professors be showing sexually arousing pictures to subjects? For science, of course.

Stephan Hamann and Kim Wallen, along with psychology graduate student Rebecca Herman, are collaborating on a project to study neural responses to visual sexual stimuli. In order to do this, they use Functional Magnetic Resonance Imaging (FMRI), a technique for measuring brain activation using an MRI scanner. This technique capitalizes on the fact that increased neural activity requires increased blood flow; changes in blood flow show up on the FMRI scans.

Wallen, professor of psychology, brings to the project his knowledge of the neurobiology of nonhuman primates, especially the mechanisms involved in female sexual behavior. Wallen was interested in how that information can be brought to bear on what is known about humans.

An assistant professor of psychology, Hamann brings his expertise in emotions, functional imaging and brain systems in humans. He is especially interested in the amygdala (located in the temporal lobe) and how that region of the brain is involved in sexual response.

“It seemed a natural confluence of our research programs,” Hamann said.

Fourteen males have participated in this project by viewing pictures while having their brains scanned. Subjects viewed arousing images and non-arousing images blocked in 20-second intervals; in other words, for 20 seconds they viewed arousing pictures, and then in the next 20 seconds they viewed non-arousing pictures, alternating for several trials. There were also trials that alternated every four seconds.

The non-arousing pictures were blurred versions of the arousing pictures, creating images that were no longer stimulating but similar to the arousing pictures in other ways. Thus, according to the researchers, brain activation present when subjects viewed the arousing stimuli—and not present when subjects viewed the non-arousing stimuli—can be attributed to the sexual nature of the pictures.

This project differs from previous research in that it examined immediate responses to sexual stimuli. Previously it was thought that in order to study sexual arousal, it was necessary to have long presentations of stimuli in order for arousal to build.

“From our point of view,” Hamann said, “a lot of interesting things have been ignored—the things that happen in the first few seconds when you are looking at sexual stimulus. From an evolutionary point of view, that might be very important: orienting toward some stimuli and not others.”

One of the project’s most striking findings thus far has been the strong activation of the amygdala. One reason this activation is important is because it was somewhat unexpected.

“Most neuroscientists think about the amygdala primarily in terms of negative emotion,” Hamann said. “So this is pointing out that there is another aspect to that [region of the brain].”

Another interesting area of activation was the thalamus. The thalamus functions as a sensory relay, which could suggest some enhanced sensory component of processing these stimuli.

The thalamus also has attentional functions; some studies of fear neurophysiology show that the amygdala works with the thalamus to modulate attention. This suggests an important attentional aspect of the stimuli presented in this study. The hippocampus, usually associated with learning and memory, was another area of activation.

Hamann and Wallen are currently testing subjects for the next (and unprecedented) step of the project—investigating the differences in brain activation between males and females. Previous research, of which there is little, has examined only the male response, they said.

“It’s an exploratory kind of study,” Hamann said. “There really isn’t a lot of neuroimaging evidence you can point to that would tell you very much about what to expect, but once we find out even the basic outline—what’s going on in the females and compare it to males—that will start to suggest all sorts of interesting questions to follow up.”

This project is supported by a Center for Behavioral Neuroscience (CBN) venture grant. The CBN supports collaborative efforts from researchers of different disciplines of neuroscience. Hamann believes the project would probably not have happened without the support of the CBN.