October 22, 2001
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,
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 stimuliand not present
when subjects viewed the non-arousing stimulican 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 ignoredthe 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 projects 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 projectinvestigating the differences in brain activation
between males and females. Previous research, of which there is little,
has examined only the male response, they said.
Its an exploratory kind of study, Hamann said. There
really isnt 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 outlinewhats going on in the females and compare
it to malesthat 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.