AbstractsPsychology

To persist, new memories must undergo a consolidation process, during which they are sensitive to disruption. This process, referred to as cellular consolidation, is posited to be completed within the first hours following learning and involves stabilization of changes in synaptic connectivity. Memories can also consolidate at the level of brain systems. Systems-consolidation is a more prolonged process involving gradual reorganization of brain systems that support memory expression, where memories that initially depend on the hippocampus increasingly come to depend on specific cortical structures. A number of recent studies have suggested that the anterior cingulate cortex (ACC) is one such cortical structure that is not required for the expression of recent memory, but becomes critical for the expression of remote memory. In addition to reorganization of the anatomical substrates of memory, memories are known to change in other ways over time. Contextual memory, initially hippocampus-dependent, can become less specific over time, whereby animals generalize conditioned responding to novel contexts. However, a number of recent studies have described how following retrieval, memories can return to a labile state, a process referred to as cellular reconsolidation. Similarly, retrieval has been found to transiently return a hippocampus-independent remote memory to a hippocampus-dependent state, a process of systems reconsolidation. Moreover, memory retrieval reactivating the hippocampus has been found to renew memory precision with reduced behavioural generalization.To date, little is known about how retrieval affects the involvement of the ACC, more specifically: (1) whether memory undergoes cellular consolidation and reconsolidation in the ACC, and if so, if this is the case for recent as well as remote memories; (2) whether ACC-dependent remote memory transiently becomes ACC-independent following retrieval; and (3) whether increased context memory generalization is mediated by the ACC. This thesis aims to answer these questions in the following two manuscripts. In all experiments, rats underwent contextual fear conditioning. The first manuscript addresses the first two questions. To answer the first question, protein-synthesis inhibitor was infused into the ACC immediately following conditioning or memory retrieval. The results indicate that the ACC is involved in cellular consolidation and reconsolidation of recent and remote contextual fear memory. To answer the second question, the ACC was pharmacologically inactivated at different time-points before testing at time-points after a reactivation trial. The results suggest that at 6 hours following memory retrieval, memory expression can be supported by either the ACC or the dorsal hippocampus (DH), whereas at 24 hours after the retrieval, the memory is once more ACC-dependent. The second manuscript examines the third question, examining the effects of memory retrieval on subsequent context generalization. The results indicate that following memory retrieval, context…