Other research suggests that hormones and biological cycles may play significant roles in fear learning and extinction.
Although some data suggest that estrogen actually enhances fear learning, says Milad, other studies suggest the opposite, that it reduces fear and anxiety. Unfortunately, the area is underinvestigated. Anxiety disorders, for example, are twice as high in women-and we can't say precisely why.
The researchers' work does provide intriguing clues, however. They have found that women with higher estrogen levels showed stronger activation of the ventromedial prefrontal cortex, a brain region key to fear control. These high-estrogen women were good at extinguishing fear. When the researchers repeated the study in rats and manipulated estrogen levels, they found that blocking estrogen impaired the animals' ability to control fear. Reintroducing estrogen caused the rats to behave as if they felt safe.
Curiously, the researchers found that men's ability to control fear was akin to that of high-estrogen women. How does it jibe, then, that women have twice the prevalence of anxiety disorders?
We don't know, says Milad, but the speculation is that estrogen alone doesn't make you a super-extinguisher. It may be the lack of the hormone that puts a woman at higher risk. If a woman's estrogen is high, she controls fear in a way comparable to men, but if her estrogen dips, as it would during a normal menstrual cycle, she may be at a higher risk for fear acquisition following a trauma or another emotion-laden incident.
Such studies by Milad and others highlight a growing interest in finely parsing the mechanisms of fear acquisition and extinction in humans. Fundamentally, though, our response to fear remains basic, a primitive emotion essential to our survival and a core response that unifies our species.
The amygdala is the amygdala, says Milad. Whether it's in Taipei or in Cedar Rapids, it's still a knee-jerk response to danger.
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