The study adds to a growing body of research in animals and humans that indicates the amygdala plays a central role in male sexual behavior, Hamann says.
"This study helps us get closer to understanding the fundamental functions of this area of the brain," Hamann says. In addition to adding to basic neuroscience knowledge, the findings potentially could have applications that could help scientists develop therapeutic measures to help people overcome sexual addictions and other dysfunctions, he says.
In the study, 14 male and 14 female participants viewed several types of sexual and social interaction images for 30 minutes. Their brain activity was then compared using functional magnetic resonance imaging (fMRI), a technology that measures neural firing through changes in blood flow.
The fMRI scans revealed significantly higher levels of activation in the amygdala, which controls emotion and motivation, in the brains of the male subjects compared to the females, despite the fact that both males and females expressed similar subjective assessments of their levels of arousal after viewing the images.
Hamann and Wallen had a separate group pre-select the images to ensure they would be equally arousing to both males and females.
"If males and females found the pictures equally arousing, you would assume they would have similar patterns of brain activation," said Hamann. "But we discovered the male brain seems to process visual sexual cues differently."
The scientists' discovery also is consistent with an evolutionary theory that natural selection spurred the development of different sexual behaviors in males and females.
"There is an advantage for males in quickly recognizing and responding to receptive females through visual cues," explains Hamann. "This allows them to maximize their mating opportunities, which increases their chances for passing on their genes."
Nature Neuroscience