Emotional Arsoual and Modulation of Multiple Memory Systems: Effects of Unconditioned and Conditioned Stressors
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Recently studies have uncovered a wealth of evidence supporting the theory that different areas of the mammalian brain mediate different types of memory. Specifically, evidence suggests that memory does not exist as a single construct and, more importantly, the different types of memory are mediated by different neuroanatomical regions. Two primary memory systems are the hippocampus-dependent cognitive memory system and the dorsolateral striatum-dependent habit memory system. Interestingly, there are a number of factors that can influence the relative use of these memory systems. One important factor that influences the relative use of multiple memory systems is emotional arousal. Emotional arousal, as defined in this body of work, is defined as a state of heightened emotion, particularly in reference to states of anxiety or stress. Decades of research have uncovered a role of emotional arousal in modulating memory. Despite the wealth of literature regarding the role of emotional arousal on cognitive function, only recently have studies investigating the role emotional arousal in the context of the multiple memory systems begun to surface. The present experiments were developed to explore the role of ethologically and physiologically relevant stressors in modulating multiple memory system. In addition, this set of experiments also introduces the idea that a fear-conditioned stimulus may modulate memory. There were three specific aims. The first aim was to determine if an ethologically-relevant stressor such as trimethylzoline, an odor component of red fox feces, can influence the relative use of multiple memory systems and modulate dorsolateral striatum-dependent memory. Additionally, this set of experiments also aimed to implicate the basolateral amygdala (BLA) in mediating this effect. The second aim was to administer the endogenous stress hormone corticosterone, as a physiologically-relevant stressor, to modulate dorsolateral striatum-dependent memory. Furthermore, these experiments attempted to implicate noradrenergic activity as necessary in mediating the glucocorticoid effect on habit memory. Finally, the last aim of this dissertation was to employ fear-conditioned stimulus to modulate memory in the same manner as a stressful unconditioned stimulus. Specifically, these experiments determined if a tone, when paired with a shock, can influence the relative use of memory and modulate dorsolateral striatum-dependent memory and further investigated the role of noradrenergic activity in mediating this effect. The findings suggest that emotional arousal, in various forms, influences the relative use of memory in similar fashion. Additionally, various forms of emotional arousal also modulate dorsolateral striatum-dependent habit memory. These results extend previous work investigating the role of emotional arousal on memory, while expanding on research specific to the dorsolateral striatum-dependent memory system. These studies also strongly suggest that the modulation of memory through emotional arousal relies on a noradrenergic activity. Overall, this body of work suggests that emotional arousal, both through unconditioned and conditioned stimuli, facilitates dorsolateral-striatum dependent habit memory.
Leong, Kah-Chung (2014). Emotional Arsoual and Modulation of Multiple Memory Systems: Effects of Unconditioned and Conditioned Stressors. Doctoral dissertation, Texas A & M University. Available electronically from