Book T of C
Chap T of C
This is the 2007 version. Click here for the 2017 chapter 02 table of contents.
Such spectacular demonstrations may be misleading. Stimulation of the amygdala sometimes triggers violence, but apparently it does not always or even typically trigger violence. Electrical stimulation of the amygdala in humans usually creates fear or anxiety, not aggressive behavior. When the amygdala is removed from laboratory animals, they show no fear. A rat with its amygdala removed "will walk up to a sleeping cat and even nibble on its ear" (Barinaga, 1992). The amygdala is connected by large neural pathways to areas of the brain responsible for defensive behaviors (Blanchard & Blanchard, 1988). Anderson and Phelps (2000) write, "A growing body of evidence from humans and other animals suggests the amygdala may be a critical neural substrate for emotional processing."
What happens when the amygdala is removed from a rat?
What were symptoms of a damaged amygdala in a human?
When the amygdala is damaged in humans, they lose their sensitivity to stimuli associated with strong emotions. For example, Adolphs, Russell, and Tranel (1999) found that a patient with "complete, bilateral damage restricted to the amygdala" was able to tell when a face was sad or happy, but he had lost his ability to discriminate between different levels of emotional arousal. He could not tell a slightly sad face from a very angry face: they all just looked "unhappy" to him. He had the same problem with happy expressions: he could not tell the difference between a face that showed very mild happiness and one that expressed great joy.
How might the amygdala be involved in shyness?
When the amygdala is overactive, it may produce oversensitivity to emotional arousal. Kagan and Snidman (1991) suggested that the amygdala might be involved in shyness. About one child in ten is shy from birth onward. A shy person may be trying to avoid unpleasant activation of the amygdala by avoiding situations that might provoke strong emotional reactions.
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