UC Santa Barbara

Recently there has been an increased interest in the lateral parietal cortex's role in successful memory retrieval. Several theories have been put forth to explain this phenomenon including the idea that this region plays a direct role in memory retrieval, temporarily storing episodic content until a decision can be made. Other explanations report a more indirect role of the parietal cortex during memory retrieval. Some of these theories include modulations of attentional systems that may guide memory retrieval or representations of subjective awareness of one's memories. According to these theories, parietal activations may assist successful memory retrieval, but are not necessary for it to occur. Although this region is consistently found to be active when memories are successfully retrieved, these results were initially difficult to reconcile with reports from neuropsychology, which show a lack of severe memory impairment when damage to this region occurs. These findings are specifically difficult for theories that assume this region is directly related to memory retrieval (i.e. the episodic buffer account), which assume this activity is necessary for successful retrieval to occur. The purpose of the experiments described in this dissertation is to test whether parietal activations are modulated by task demands that should not affect the amount of episodic content retrieved. These task demands include modifying the way retrieval states are operationalized and varying the base rates of studied items presented at test. Although these procedural changes should affect extra-mnemonic cognitive processes, there is no reason to assume they should affect the amount of mnemonic information retrieved. Results from these studies in fact do show a modulation of both dorsal and ventral lateral parietal activations based on these procedural manipulations. These results are difficult to explain with an episodic buffer account of parietal activity. Instead, the results point to a more indirect role of parietal involvement in memory retrieval and are the most in line with the idea of this area representing the subjective awareness that can accompany successful retrieval, particularly during recollection. When these results are compared to results from neuropsychology, an extra-mnemonic role for the parietal cortex, particularly one associated with the subjective experience of retrieved content, appears to be the most parsimonious explanation of the patient findings. However, a subjective awareness account of parietal activity cannot adequately explain all of the findings from the literature, and most likely is only part of the story. The parietal cortex is an extremely heterogeneous area, both in structural and functional connectivity. The full story of the parietal cortex's role in memory retrieval will most likely be explained with a variety of theories. Increased levels of spatial segregation of the parietal cortex into distinct functional sub-regions will most likely reveal a myriad of functional roles that this region is playing during the complex cognitive process that is memory retrieval.