Possible Genetic Basis for Fear Discovered

Ahmad R. Hariri, Ph.D., and colleagues at the National Institute of Mental Health looked at how subjects with variations in the serotonin transporter (5-HTT) gene (which mediates anxiety behavioral traits) reacted to fearful stimuli. Subjects with a short allele on the promoter region of 5-HTT have lower levels of serotonin transporter function and thus may be more prone to anxiety than those with a long allele in the same region. The researchers hypothesized that subjects with the short allele would show a greater fear response in the amygdala region that those with a longer allele.

Researchers performed functional magnetic resonance imaging (fMRI) on two groups of patients, one with the short allele, while displaying images of either fearful or angry faces. Subjects were asked to match the affect of the facial images to a third facial image.

Comparison of fMRIs for the two groups showed that subjects with the short allele had greater activity in the right amygdala region than those with the long allele. The researchers speculated that this may also be related to the role of the right hemisphere of the brain in processing facial expressions. (Although these researchers speculated that greater activity in the right amygdala may be related to the role of the brain’s right hemisphere in processing facial expressions, other researchers have found that right hemisphere activation reflects negative emotions and that the amygdala is especially important in mediating the fear response. – Ed.) There were no differences by gender or in task performance. Furthermore, there were no differences in anxiety or fear traits between two groups as measured on the Tridimensional Personality Questionnaire, leading the authors to emphasize the importance of direct assay of brain function in identifying a phenotype for human emotion.

Ref: Psychiatric Times, Oct. 2007