The Human Amygdala: What Does It Do?

Elizabeth A. Phelps and Adam K. Anderson

Until recently, our understanding of the neural processes underlying emotion was derived primarily from research with animals other than humans. Although these animal models have been extremely useful in identifying brain systems, few would disagree that the emotional life of humans may not lend itself to easy analogy across species. For this reason, it is especially important that animal systems of the neural basis of emotion be tested for their applicability to human experience. One brain structure that has emerged as a focus of emotion research in non-human animals is the amygdala, a small almond-shaped structure located anterior to the hipppocampus in the medial temporal lobe. Studies of the role of the amygdala in non-human animals suggest that it may be necessary for learning or assessing the emotional significance of events. In humans, the function of the amygdala has been difficult to study for several reasons. Firstly, research into brain-behavior correlates in humans has relied heavily on patients with lesions, and discrete lesions to the amygdala are extremely rare. Patients with amygdala damage always have other brain abnormalities or congenital disorders that must be taken into consideration when interpreting results. Secondly, studies of the amygdala in humans using new imaging techniques have been slow to emerge because the amygdala is a small structure, close in size to the resolution of Positron Emission Tomography (PET), and in a location that is subject to significant noise in functional Magnetic Resonance Imaging (fMRI). Lastly, emotion is a broad concept that is not well defined in traditional psychology, making the selection of appropriate tasks for studying emotion difficult. In spite of these drawbacks, a body of literature on the role of the amygdala in humans is beginning to emerge. Studies of the behavioral role of the human amygdala generally fall into two categories: emotional memory and the evaluation of emotional stimuli, and we shall consider these in turn.