In sum, norepinephrine plays a crucial role in the emotional enhancement of memory (McGaugh, 2000), and contributes to long-term alterations in synaptic strength, gene transcription, and other processes necessary for learning (Berridge & Waterhouse, 2003).Furthermore, the amygdala plays a role in central regulation of HR, as projections from the central nucleus of the amygdala innervate the nucleu