2.5 The amygdala and generalised anxiety disorder

There is some evidence that the amygdalas of people with generalised anxiety disorder (GAD) may be abnormally active, so that they feel anxious and fearful without apparent reason. For instance, Nitschke et al. (2009) recorded activity in the amygdalas of patients with GAD and controls without GAD as they looked at images of unpleasant objects such as mutilated bodies, or neutral objects such as fire hydrants.

A few seconds before seeing the images, all participants received a cue to let them know whether to expect an unpleasant or neutral photograph. Nitschke et al. found that the amygdala activation of those with GAD did not differ significantly from that of controls (without GAD) when they were viewing unpleasant or neutral images (Figure 7).

Figure 7  Anticipatory amygdala activation differentiating participants with generalised anxiety disorder (GAD) and healthy comparison subjects. Participants with GAD had significantly greater activation in the amygdala on both sides of the brain compared to healthy controls without GAD. This was the case both in aversive trials (in which a cue predicting an aversive image was presented) and in neutral trials (in which a cue predicting a neutral image was presented. (The amygdalas are circled.)

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The figure comprises a black and white image of the brain, in which brain activity in response to cuing of an aversive or neutral stimulus is shown on a colour scale. There is a concentration of activity in the amygdalas. Below the brain image are two vertical bar charts showing the increase in activation in both the left and right amygdalas in a group of 14 participants with GAD and in a group of 12 control participants. The vertical axes are marked increase in activation of amygdala and are marked from zero to 0.4 at intervals of 0.2 arbitrary units. For both controls and participants with GAD, there was no difference in anticipatory amygdala activation between the groups that subsequently underwent aversive and neutral trials. But the increase in activation in the GAD groups was double that of the control groups (around 0.2 compared to 0.1 respectively).

Figure 7  Anticipatory amygdala activation differentiating participants with generalised anxiety disorder (GAD) and healthy comparison ...

However, the amygdalas of GAD patients became much more active than those of controls when they were shown cues signalling that a negative or neutral image would be appearing.

Currently it is not known why the amygdalas of patients with GAD are over-active. As GAD has a heritability of 30%–40%, genetic factors clearly play some part. However, stress and its ‘boosting’ effect on the amygdala, discussed above, may also be important.