Neural mechanisms underlying the effects of emotional arousal on memory

Emotional events (e.g., seeing a snake while hiking) typically stay in the memory longer and in more detail than neutral ones (e.g., seeing a bird while hik-ing). This emotion-induced memory enhancement has been attributed to the amyg-dala’s modulation on other brain regions, such as the medial temporal lobe and visual cortices. In line with this amygdala modulation hypothesis, previous brain imaging research revealed enhanced amygdala activity when encoding and retriev-ing emotional stimuli compared with non-emotional stimuli. However, emotion does not always enhance memory. Indeed, researchers have long been aware that emotion sometimes enhances and sometimes impairs memory. Yet, the underlying mechanisms of the opposing effects of emotion are relatively unknown. For example, if the amygdala’s modulation on other brain regions is critical in the emotion- memory interaction, how does it result in the enhancement effects for some aspects, while impairing other aspects of memory? In this chapter, we argue an alternative possibility: that norepinephrine released by the locus coeruleus under arousal plays a critical role in the complex effects of emotion on memory