What is the Amygdala?

The limbic system is a set of midline structures from the telencephalon, diencephalon and mesencephalon in the temporal lobe that encircles both sides of the thalamus. The limbic system as a circuit has been involved in regulating motivated behaviors including ‘fight or flight’, feeding and sexual behavior. At the core of the limbic circuit lie the major structures, including the fornix, cingulate cortex, septum and the amygdala.[1]

The amygdala is an almond-shaped nucleus in the anterior temporal lobe seated within the uncus. The word amygdala is in fact actually Latin for “almond”. The amygdala is not just a single structure but a group commonly divided into the right amygdala, left amygdala and the amygdala subnuclei. Although it is conceptualized as part of the limbic system, the amygdala reciprocally connects with many different brain regions including the brain stem, hippocampus, parahippocampal gyrus, septal nuclei, hypothalamus, thalamus, striatum, cingulate gyrus and out to the orbital frontal cortex.[1] The amygdala coordinates autonomic, endocrine and behavioral responses to stimuli from the environment, and most particularly it integrates inputs that stem from emotional content.[2]

Amygdala Function

The amygdala’s coordinated responses to the environment are considered critical for evolutionary adaptation and species survival. It coordinates responses to stress and in particular, conditioned emotional responses.[3] However, amygdala related responses can be dysregulated and over time prove problematic.[1] The negative valence behaviors and maladaptive responses of the amygdala are probably a part of its appeal for scientific inquiry. The amygdala as a stimulus-response coordinator makes it a good choice for manipulation in behavioral neuroscience experiments. Experimental research models manipulate experimental variables, or independent variables, to test whether or not those controlled variations result in changes to the dependent variable or variables which may include various types of fear and stress-related behavioral stimulus responses.

If an animal amygdala receives direct electrical stimulation via an electrode, the animal will respond with fear, freezing or aggressive behaviors depending on the targeted amygdala subregion.[4] If the amygdala is removed, the animal no longer responds to fear and stress stimuli. Although the amygdala is implicated in survival stress responses it does not create and modulate those responses acting along. Simple manipulations that include lesioning, neurochemical or genetic knockouts that effectively ‘remove’ all amygdaloidal functioning, may also disrupt and damage other brain structures connected to the amygdala.