Parabrachial-to-amygdala control of aversive learning

Elucidating neuronal circuitry mechanisms underlying adaptive behaviors and memory formation is fundamental to understanding brain function. Pavlovian fear conditioning studies have provided important insights into the neuronal mechanisms of conditioned and unconditioned stimuli in the amygdala, and their associative mechanisms and plasticity have been intensively studied. Recent advances in optogenetics and pharmacogenetics combined with genetic manipulation tools, however, reveal new insights into unconditioned stimuli themselves. Importantly, how unconditioned stimuli are transmitted and regulated has been explored at the circuitry level. This review focuses on recent advances and earlier studies on the specific neuronal pathways regulating unconditioned stimulus information processing in intra-amygdala and extra-amygdala circuits, and provides a working model of the neural tuning mechanisms underlying adaptive behaviors.