The amygdala and depression

Professor Wayne Drevets outlines the amygdala's importance to the neurobiology of depression. He concludes that stimulation of the amygdala can elicit depression-like emotional experiences.

One of the structures in the brain that has been most closely associated with depression has been the amygdala. The term amygdala literally means almond, because this structure has about the size and shape of an almond. The amygdala has been known to be an important brain region in evaluating the emotional significance of different kinds of stimuli, including stimuli that might represent a threat or that might have social significance or that might have reward value. The amygdala has been an area where we’ve been able to show abnormalities in metabolism, blood flow and also responses to different classes of emotional stimuli. So for example the amygdala is overly active in people with depression when you show them sad stimuli, but it’s under-active when you show them positive stimuli like things that they would be rewarded by, or even smiling faces. So you see evidence for this differential processing of positive versus negative stimuli in this structure in depression. The amygdala also plays a role then in organizing the emotional experience in expression. It gets involved in organizing the endocrine response to stressors and threats, the autonomic response to stressors and threats and the behavioral and mood response to stressors and threats. In all of these domains, you can show abnormalities in depression that really resemble a state where you’ve got an excess of amygdala activity going on. The stress hormones are excessively secreted in depression, the autonomic pattern is imbalanced in a way that would be associated with an increased amygdala activity. We’ve got too much sympathetic to parasympathetic [activation], and then the behavioral response of social isolation and feeling anxious/tense is also consistent with how one would respond with an overactive amygdala. Indeed in humans when neurosurgeons have stimulated the amygdala, they actually can elicit the whole range of emotional experiences that people with depression will describe.