DescriptionThe amygdala has long been known to play a critical role in emotional processing, in particular fear. In this respect it has been shown to play three major roles. First, it mediates the facilitating effects of emotional arousal in memory formation. Second, it is the site of storage for emotional memories themselves, in particular fear. And lastly, it mediates the expression of fear responses. The work presented in this thesis investigates each of these different functions of the amygdala. In the first chapter, I examined how glucocorticoids, which are known to enhance memory consolidation through their actions on the amygdala, affect the electrophysiological properties of the amygdala neurons. I show that glucocorticoids increase the excitability of principal amygdala neurons. In the second chapter, I investigated the role of REM sleep in consolidation of emotional memories. To this end, I examined the interactions between the amygdala, medial prefrontal cortex and hippocampus during sleep following fear learning. I show that theta coordination in this network during REM sleep participates in the consolidation of fear memories. In the third and fourth chapters, I investigated the role of the amygdala in storage and expression of fear memories. I show the different involvements of each amygdala nuclei in mediating conditioned fear expression. Lastly, I investigated the role of anxiety in fear learning. I show that anxiety can interfere with fear learning by resulting in fear generalization to safe cues and environments.