““Joseph LeDoux at New York University has shown how the BLA learns fear.fn14,20 Expose a rat to an innate trigger of fear—a shock. When this “unconditioned stimulus” occurs, the central amygdala activates, stress hormones are secreted, the sympathetic nervous system mobilizes, and, as a clear end point, the rat freezes in place—“What was that? What do I do?” Now do some conditioning. Before each shock, expose the rat to a stimulus that normally does not evoke fear, such as a tone. And with repeated coupling of the tone (the conditioned stimulus) with the shock (the unconditioned one), fear conditioning occurs—the sound of the tone alone elicits freezing, stress hormone release, and so on.fn15””
