A team of American researchers has found that an emotion circuit in the brain activates more in girls as they grow older, but not in boys when they are sizing up their respective peers.
Dr. Daniel Pine of the National Institute of Mental Health (NIMH), part of National Institutes of Health, has revealed that the circuit is made up of the nucleus accumbens (reward and motivation), hypothalamus (hormonal activation), hippocampus (social memory) and insula (visceral/subjective feelings).
He says that the study shows how emotion circuitry diverges in the male and female brain during a developmental stage in which girls are at increased risk for developing mood and anxiety disorders.
Working in collaboration with Georgia State University experts, the researchers ostensibly involved 34 psychiatrically healthy males and females, aged 9 to 17, in a study of teenagers' communications via Internet chat rooms.
The researchers say that the subjects were told that after an fMRI (functional magnetic resonance imaging) scan, which visualizes brain activity, they would chat online with another teen from a collaborating study site.
They reveal that each participant was asked to rate his or her interest in communicating with each of 40 teens presented on a computer screen, so that they could be matched with a high interest participant.
After two weeks, the teens once again viewed the same faces while in an fMRI scanner, but this time they were asked to instead rate how interested they surmised each of the other prospective chatters would be in interacting with them.
Only after they exited the scanner did they learn that, in fact, the faces were of actors, not study participants, and that there would be no Internet chat.
The scenario was intended to keep the teens engaged-maintain a high level of anticipation/motivation-during the tasks, and that helped ensure that the scanner would detect contrasts in brain circuit responses to high interest versus low interest peers.
While the researchers selected the faces for their happy expressions, their attractiveness was random, so that they appeared to be a mix of typical peers encountered by teens.
The researchers observed that the teen participants deemed the same faces they initially chose as high interest to be the peers most interested in interacting with them.
According to them, older participants tended to choose more faces of the opposite sex than younger ones.
Upon appraising anticipated interest from peers of high interest compared with low interest, the researchers observed that older girls showed more brain activity than their younger counterparts in circuitry that processes social emotion.
"This developmental shift suggested a change in socio-emotional calculus from avoidance to approach," noted Pine.
Boys, on the other hand, showed little change in the activity of most of these circuit areas with age, except for a decrease in activation of the insula, something that may reflect a waning of interpersonal emotional ties over time in teenage males, as they shift their interest to groups, suggest Pine and colleagues.
"In females, absence of activation in areas associated with mood and anxiety disorders, such as the amygdala, suggests that emotional responses to peers may be driven more by a brain network related to approach than to one related to fear and withdrawal. This reflects resilience to psychosocial stress among healthy female adolescents during this vulnerable period," said Pine.
The study has been published in the journal Child Development.