Amygdala neuronal ensembles dynamically encode behavioral states

Internal states, including affective or homeostatic states, are important behavioral motivators. The amygdala is a key brain region involved in the regulation of motivated behaviors, yet how distinct internal states are represented in amygdala circuits is not known. Here, by imaging somatic neural calcium dynamics in freely moving mice, we demonstrate that changes in the relative activity levels of two major, non-overlapping populations of principal neurons in the basal nucleus of the amygdala (BA) predict switches between exploratory and anxiety-like or defensive behavioral states across different environments. Moreover, we found that the amygdala widely broadcasts internal state information via several output pathways to larger brain networks, and that sensory responses in the BA were not correlated with behavioral states. Our data indicate that the brain processes external stimuli and internal states in an orthogonal manner, which may facilitate rapid and flexible selection of appropriate, state-dependent behavioral responses.