Penn Scientists Map and Measure the Seat of Impulsive
Behavior in the Brain
PA) -- There is a sound neurological basis for the cliché
that men are more aggressive than women, according to
new findings by scientists at the University of Pennsylvania
School of Medicine.
Using magnetic resonance imaging (MRI) scans, the Penn
scientists illustrated for the first time that the relative
size of the sections of the brain known to constrain
aggression and monitor behavior is larger in women than
The research, by Ruben C. Gur, PhD, and Raquel
E. Gur, MD, PhD, and their colleagues in Penn's
Department of Psychiatry and the Department of Epidemiology,
is published in the recent issue of the Journal of the
The findings provide a new research path for therapies
that may eventually help psychiatric patients control
inappropriate aggression and dangerous patterns of impulsive
behavior. They also bolster previous work by the Gurs
demonstrating that although some gender differences
develop as result of adaptive patterns of socialization,
other distinctions are biologically based and probably
"As scientists become more capable of mapping the
functions of activity in various parts of the brain,
we are discovering a variety of differences in the way
men and women's brains are structured and how they operate,"
said Ruben Gur, first author of the study.
"Perhaps the most salient emotional difference
between men and women, dwarfing all other differences,
is aggression," he said. "This study affords
us neurobiological evidence that women may have a better
brain capacity than men for actually 'censoring' their
aggressive and anger responses."
In the Gurs' work, they relied on established scientific
findings that human emotions are stimulated and regulated
through a network that extends through much of the limbic
system at the base of the brain (the region encompassing
the amygdala, hypothalamus and mesocorticolimbic dopamine
systems), and then upward and forward into the region
around the eyes and forehead (the orbital and dorsolateral
frontal area), and under the temples (the parietal and
The amygdala is involved in emotional behavior related
to arousal and excitement, while the orbital frontal
region is involved in the modulation of aggression.
The Gurs' study measured the ratio of orbital to amygdala
volume in a sample of 116 right-handed, healthy adults
younger than 50 years of age; 57 subjects were male
and 59 were female. Once the scientists adjusted their
measurements to allow for the difference between men
and women in physical size, they found that the women's
brains had a significantly higher volume of orbital
frontal cortex in proportion to amygdala volume than
did the brains of the men.
"Because men and women differ in the way they process
the emotions associated with perception, experience,
expression, and most particularly in aggression, our
belief is that the proportional difference in size in
the region of the brain that governs behavior, compared
to the region related to impulsiveness, may be a major
factor in determining what is often considered 'gendered-related'
behavior," Raquel Gur said.
Others Penn investigators participating in the study
were Faith Gunning-Dixon, PhD, and Warren
B. Bilker, PhD, of the Department of Epidemiology.
The study was funded by a grant from the National Institutes
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