How "Hot" Emotional Brain Interferes With "Cool" Processing
DURHAM, N.C. -- For the first time, researchers have seen in
action how the "hot" emotional centers of the brain can
interfere with "cool" cognitive processes such as those
involved in memory tasks. Their functional magnetic resonance
imaging (fMRI) images of human volunteers exposed to emotional
distraction revealed a "see-saw" effect, in which activation of
emotional centers damped activity in the "executive" centers
responsible for such processing.
The findings of the Duke University Medical Center
researchers provide insight into the basic brain mechanisms
responsible for the distraction caused by emotional stimuli
that are irrelevant to a task. Moreover, they said, the
findings offer a new approach to understanding how people with
depression and post-traumatic stress disorder cope with
traumatic events and memories. It is known that people with
such problems are far more affected by emotional
Development of new drugs to alleviate, for example, the
haunting memories of PTSD sufferers will be aided by the fMRI
technique the researchers developed to precisely measure this
distraction, they said.
The researchers, Florin Dolcos and Gregory McCarthy,
published their findings in the Feb. 15, 2006, issue of the
Journal of Neuroscience. Their work was sponsored by the
National Institutes of Health and the Veterans Administration.
Dolcos is a postdoctoral fellow and McCarthy is director of the
Duke-UNC Brain Imaging and Analysis Center <
http://www.biac.duke.edu />, where the studies took
In their experiments, the researchers asked volunteer
subjects to memorize sets of images of three human faces. Next,
they exposed the subjects to one of three types of distracters
-- emotional images such as injured people or aggressive
behavior; neutral images such as people shopping or working;
and scrambled images that meant nothing. The subjects were then
showed a face image and asked to determine whether it was one
of the original "to-be-memorized" faces or a new face.
Throughout the tests, the subjects' brains were scanned
using fMRI. This widely used technique involves using harmless
magnetic fields and radio waves to scan the brain to detect
levels of blood flow, which indicates increased or decreased
In earlier studies, the researchers had found that emotional
images activated a "ventral affective system" in the brain that
encompasses regions involved in emotional processing. In
contrast, they found, cognitive tasks involving memory
processes activated a "dorsal executive system." To their
surprise, the researchers also found that the emotional
distracters not only activated the ventral system, but also
deactivated the dorsal regions.
In the new study, the researchers observed the same patterns
of activation and deactivation of the regions. The emotional
images produced greater activation of the ventral system and
deactivation of the dorsal system than did the neutral or
scrambled images, they found.
But most importantly, they found graded behavioral effects
of the images. The emotional distracters produced the most
detrimental effect on memory performance, the neutral
distracters impaired performance to a lesser extent; and the
scrambled images impaired performance very little. "Along with
the fMRI results, these findings provide the first direct
evidence concerning the neural mechanisms mediating cognitive
interference by emotional distraction," said Dolcos.
"The design of these experiments gave us an excellent chance
to fill in a missing link in our earlier studies," said Dolcos.
"It enabled us to determine whether there was, indeed, a
behavioral connection between deactivation of the dorsal system
and impaired performance.
"The experimental design mimicked the kind of distraction
people experience in everyday life," Dolcos added. "For example
someone driving on a highway, attempting to pay attention to
the driving task might encounter an emotional distracter such
as an accident. As everybody knows, at that moment drivers lose
focus on the task."
"Also, the three types of distracters gave us good controls,
which allowed us to clearly establish that the observed effects
were due to the presence of emotional distraction rather than
to the presence of other meaningful (neutral images) or
meaningless (scrambled images) distracters."
The researchers also found individual differences among the
subjects in their response to the images. Those people who
showed greater activity in a brain region associated with the
inhibition of response to emotional stimuli rated the emotional
distracters as less distracting. Said Dolcos, "One
interpretation of this finding is that, because this region is
associated with inhibitory process, people who engage that
region more could cope better with distracting emotions."
McCarthy said that the results of their study will likely
have important implications for understanding of anxiety
disorders. "Our hypothesis has been that people suffering from
such anxiety disorders such as depression and PTSD, may see the
world differently than other people, and that a distracter
associated with trauma may grab control of brain processing and
essentially take off-line those areas of the brain we use to
stay on task. It's as if when you're sad, the world seems
sadder and all you see is bad news."
"Our aim is to reverse that with drug treatment, so we're
using these kinds of studies to determine whether particular
antidepressants influence the response of that ventral system.
And what is particularly exciting is that this method allows us
to look directly at the neurological target of the drug and not
have to try to measure the more nebulous behavioral response.
So, we can detect a sub-threshold response to such drugs, which
will help us understand whether we're going in the right
direction in terms of drug development."
Such studies are being carried out in Veterans
Administration-supported Mental Illness Research, Education,
and Clinical Center, which McCarthy directs. That center aims
at using genetics, brain imaging and neuropsychological and
psychiatric techniques to understand PTSD and related