A key area in the brains of people who displayed an inhibited temperament as toddlers shows a greater response to new faces than does the same brain area in adults who were uninhibited early in life, according to a study by researchers from Massachusetts General Hospital (MGH). The imaging studies of the amygdala – a part of the brain that responds to events requiring extra vigilance – appear in the June 20 issue of Science.
"Our findings both support the theory that differences in temperament are related to differences in amygdala function, something earlier technology could not prove, and show that the footprint of temperamental differences observed when people are younger persist and can be measured when they get older," says Carl Schwartz, MD, director of the developmental psychopathology lab in the MGH Psychiatric Neuroscience Program, the paper's first author. "In a way, this research is the neuroscientist's version of the 'Seven-Up' movies," he adds, referring to a well-known series of British documentaries that have revisited a group of people every seven years for more than 40 years.
In psychological terms, temperament refers to a stable emotional and behavioral profile that is observed in infancy and partially controlled by genetic factors. One of the most carefully studied temperamental measures relates to a child's typical response to unfamiliar people, objects and situations. It usually is described with terms such as shyness versus sociability, caution versus boldness, or withdrawal versus approach. The two extremes of this measurement define types of children called inhibited and uninhibited by Jerome Kagan, PhD, professor of Psychology at Harvard University, a co-author of the current study.
The study participants were 22 young adults who, as children, had participated in Kagan's earlier research. Thirteen of the participants had been determined to be inhibited as infants, and nine were categorized as uninhibited. In the first phase of the current study, functional MR images (fMRI) were taken while participants viewed a random series of six faces that were presented several times. In the test phase, participants viewed a larger number of faces, some of which were totally new and some that were repeated from the first phase. All of the faces that the participants viewed had expressions that were neutral and not characterized by any emotion.
While some increase in amygdala response to strange faces is normal, the inhibited participants showed a significantly greater response to the unfamiliar faces than did the uninhibited participants. Two of the inhibited participants previously had been diagnosed with the anxiety disorder social phobia, but even when their results were removed from analysis, the inhibited groups showed much greater amygdala response.
"It's been theorized that the behavioral differences that characterize inhibited and uninhibited children may relate to the amygdala's response to novelty, and our study supports that concept," says Schwartz, who is assistant professor of Psychiatry at Harvard Medical School. "This was a modest study that needs to be confirmed in a larger population, something we are hoping to receive the resources to carry out."
The researchers also note that the current findings could complicate the interpretation of psychiatric imaging studies. Schwartz notes, "There are many imaging studies that have compared people with anxiety disorders such as panic disorder and social phobia to normal controls and found increased amygdalar activity.
While the conventional interpretation of such studies is to regard these differences as markers of the illness, our results suggest that this brain activity may in fact be a marker for the continued influence of temperamental risk factors persisting from infancy."
"These findings may reflect a difference in vulnerability that can be compensated for or exacerbated by environment and experience," says Scott Rauch, MD, MGH director of psychiatric neuroimaging, another co-author of the Science paper.
The report's other authors are Christopher Wright, MD, and Lisa Shin, PhD, of the MGH. The research was supported by grants from the Milton Fund of Harvard University and the Mental Illness and Neuroscience Discovery (MIND) Institute.
Massachusetts General Hospital, established in 1811, is the original and largest teaching hospital of Harvard Medical School. The MGH conducts the largest hospital-based research program in the United States, with an annual research budget of more than $350 million and major research centers in AIDS, cardiovascular research, cancer, cutaneous biology, medical imaging, neurodegenerative disorders, transplantation biology and photomedicine. In 1994, MGH and Brigham and Women's Hospital joined to form Partners HealthCare System, an integrated health care delivery system comprising the two academic medical centers, specialty and community hospitals, a network of physician groups, and nonacute and home health services.
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