Final answer:
The amygdala is the region of the brain that shows decreased volume in people with panic disorder.
Step-by-step explanation:
The region of the brain that shows decreased volume in people with panic disorder is the amygdala. The amygdala is part of the limbic system, which is responsible for processing emotions. It has been found that individuals with panic disorder have increased amygdala activity, which is associated with fear and anxiety.