Individuals suffering from anxiety and severe shyness in social situations consistently respond intensely to stress, and show signs of being anxious even in situations that others find safe, according to new research published online July 2 in PLoS ONE.
The HealthEmotions Research Institute and department of psychiatry at the University of Wisconsin (UW) School of Medicine and Public Health conducted the study.
Ned Kalin, chairman of the UW Department of Psychiatry and HealthEmotions Research Institute, in collaboration with graduate student Andrew Fox and others, examined brain activity, anxious behavior and stress hormones in adolescent rhesus monkeys, which have long been used as a model to understand anxious temperament in human children.
The anxious temperament is considered to be an early predictor of the later risk to develop anxiety, depression and drug abuse related to self medicating, according to the authors.
Kalin and colleagues found that subjects with the most anxious temperaments showed higher activity in the amygdala, a part of the brain that regulates emotion and triggers reactions to anxiety, such as the fight-or-flight response. Anxious monkeys had more metabolic activity in the amygdala in both secure and threatening situations, the researchers noted.
Rhesus monkeys were graded on their anxious temperament and then exposed to situations that ranged from being secure at home with their cage-mates, to being alone, to being confronted by an unfamiliar person who stood in front of the monkey presenting a facial profile to the monkey while avoiding eye contact.
The adolescent monkeys received an injection of FDG. Whether in a secure environment or a more uncertain and possibly scary one, the nervous monkeys had more brain activity in the amygdala and surrounding "stress response" parts of the brain. The increased amygdala activity corresponded to higher levels of "freezing" behavior, fewer vocalizations and higher levels of the stress hormone cortisol in the anxious monkeys, according to the researchers.
After a year and a half, follow-up testing results revealed anxious monkeys still were more stressed out than their calmer peers when judged by the behavioral and physiological measures.
"We're looking for better ways to diagnose and treat mental illness," explained Kalin. "We're trying to understand how the brain influences mood, reactions to stress and physical health."
The current research suggests that the reason is it is hard for someone with an anxious temperament to "calm down" is because they are wired in a way that tends to keep them tense and anxious, Kalin concluded.