Investigation of the Neural Basis of Order and Item Memory: Roles of Hippocampus, Prelimbic Cortex, and Perirhinal Cortex

The field of research devoted to studying the neural basis of episodic memory is relatively new, and only very recently has been operationalized for study in non-human species. In this dissertation, episodic memory is operationally defined as memory for sequences of events in the spatial and/or temporal context in which they occurred. In a series of experiments, I examined memory for items and the order in which odor events occur over varying temporal domains. I used these approaches to help elucidate the roles of HC, PL, and PER in episodic memory. First, I used a novel odor recognition paradigm to probe item memory for social and non-social odors using varying retention intervals from 5 min to 48 hr. In this study, I found that HC lesions do not affect odor recognition memory for both odor types at all retention intervals. However, I found that PER lesions induced long-term memory deficits for social odors. These data implicate a role for PER in mnemonic processes for highly overlapping, but not distinctive, stimuli. Second, I designed a new behavioral paradigm to assess memory for sequences of odors. This ethologically-relevant task is a non-rewarded, incidentally encoded, trial-unique paradigm that can assess both order and item memory following the presentation of a sequence of odors. Using this method, I found that lesions to HC, PL, and PER, but not V2, induced specific deficits for order, but not item memory. Altogether, these data contribute to a larger understanding of the roles these structures play in temporal context, suggesting a critical role for HC, PL, and PER in sequence memory and ultimately episodic memory