The scans showed that animals that called the most had more activity in the right prefrontal cortex and less in the amygdala. In contrast, those monkeys that called less frequently had less prefrontal cortex activity and more amygdala activity.
"Simply measuring brain activity in these two regions allowed us to predict with nearly 80 percent accuracy how much each individual monkey called for help," says Kalin.
The researchers were somewhat surprised to find reduced activity in the amygdalas of the most vocal animals, since increased amygdala activity is associated with fear and stressful states. It would be logical to expect that the animals that were most vocal would also be the most frightened.
"But in our earlier research, we showed that some monkeys will become inhibited and freeze when they're frightened, especially when a predator is nearby and the monkey believes that it hasn't yet been discovered by the predator," Kalin says. "We observed that the greater the fear, the less likely it was that animals would call for help, at least under certain circumstances. If you haven't been discovered by a predator lurking nearby, it's not a good idea to draw attention to yourself by crying out for help."
The situation may be very similar for humans, Kalin says, and may provide a framework for understanding differences in emotional expressivity.
"People who are less secure and more sensitive to potential threat are likely to have increased amygdala activity that may inhibit their urge to ask for help, which is related to right prefrontal cortex activity," he says.
On the other hand, he adds, "
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Contact: Dian Land
dj.land@hosp.wisc.edu
608-263-9893
University of Wisconsin-Madison
7-Mar-2005