You're biking home alone through the dark and you're afraid someone will chase you. You are afraid of spiders, heights or small spaces. Do these things ever bother you? Probably the above fears appeal to you more if you are a woman, unless your amygdala is damaged.... But if so, are you never afraid again? Research showed the following:
Women are more anxious than men
Anxiety-related disorders are at least twice as common in women than in men. The amygdala is a small nucleus in the brain that is instrumental in regulating anxiety. This brain structure responds more strongly to fearful information in women than in men.
But why is that? In one study, 80 men and women were given norepinephrine and glucocorticoids; a neurotransmitter and a hormone released in the body in response to stress. There was also a control group administered a placebo. After this, the subjects had to indicate the degree of anxiety in an fMRI scanner for pictures of neutral and fearful faces.
What transpired? Noradrenaline increased amygdala activity in women, while in men it led to a decrease in activity. In women, moreover, it also caused reduced orbitofrontal cortex activity. Because the amygdala is more associated with a reflex response, and the orbitofrontal cortex then makes an analysis of the emotional information, norepinephrine thus caused the reflex system to be enhanced in women, while the system that makes a comprehensive analysis was attenuated. In men, on the other hand, norepinephrine caused a weakening of activity in the amygdala. This difference was also observable in behaviour; women scored faces higher on anxiety, while men gave lower ratings. The hormone had no effect on either women or men.
The difference in response to norepinephrine is likely the biological mechanism that may explain why women are more likely to have anxiety disorders than men.
The amygdala does not account for all anxiety
So, the amygdala plays a vital role in the perception of anxiety and panic. When people have damage to the amygdala, they do not respond to external fearful stimuli. Furthermore, they cannot assess danger in a threatening situation. But when this fear is triggered internally they do show an anxiety response.
Researchers showed this in a study where patients had to breathe air that consisted of 35% carbon dioxide (CO2) (for comparison, normal air consists of 0.03% CO2). This method is used more often in research to elicit an anxiety response. When a person ingests such a high level of CO2, a shortage of oxygen occurs, triggering a panic response. The researchers' expectation was that these patients would show a weaker fear response than people who still have an intact amygdala.
However, the opposite turned out to be the case. The patients did show a fear response as a result of the CO2 inhalation. This research shows that the amygdala is not necessary for experiencing fear. The researchers conclude that it appears that the amygdala is necessary for fear elicited by external stimuli (from the environment), but not for fear elicited internally (by the body).
But not everything becomes clear from anxiety studies yet, because....
Coincidentally, the subjects in this latest study were all three women. The question, then, is whether exactly the same outcome can be found when this study is conducted with men. Therefore, the lack of testing both male and female subjects in anxiety research is exactly what has concerned researchers in recent years. Even though there are several studies that show different fear responses between men and women, more research is needed to find out exactly how this is caused (on a hormonal level). This is important information that is needed to properly help both men and women with anxiety disorders.
This article is based on old published brainmatters articles written by Lorraine Fliek: Damage to the amygdala and still anxious (27-2-13) & Noradrenaline causes opposite fear perception in women and men (5-4-13) - Editor: Loes Beckers