The Role of the Posterior Parietal Cortex in Subjective and Objective Episodic Memory Recollection

The purpose of this project was to compare the Attention to Memory (AtoM) and the Episodic Buffer (EB) Models. The AtoM model proposes that the ventral parietal cortex (VPC) and dorsal parietal cortex (DPC) are responsive to bottom-up and top- down attention to memory, respectively, (Cabeza, 2008; Cabeza et al., 2008; Ciaramelli et al., 2008). The EB model, on the other hand, proposes that the VPC is involved in the episodic buffer component of Baddeley\u27s working memory model (Vilberg & Rugg, 2008). Using objective (source) and subjective (Remember/Know) retrieval tasks, specific patterns of PPC activity were posited based on the propositions of the AtoM model. These expectations included greater VPC activity for Remember and False Alarms compared to Correct Rejections and Subjective Know, greater DPC activity for Know and Objective Remember compared to Subjective Remember and correct rejections, and no difference in VPC activity for remembering both font and color compared to remembering only one contextual detail. During encoding participants saw words in one of two colors, red or yellow, and in one of two fonts, curvy or straight, and were required to indicate the color the word was presented in. Following each encoding scan participants performed either an Objective or Subjective retrieval task. During Objective retrieval task, participants performed a forced-choice source memory test choosing the word with the correct fontand color or the new option. During Subjective retrieval participants were presented with the word in a neutral font and white color and performed a Remember/Know test. On the Subjective retrieval task both VPC and DPC were active for recollection compared to familiar items and Correct Rejections. On the Objective retrieval task the DPC was active for all correct old responses. Neither the VPC nor the DPC were significantly active for False Alarms on both the Subjective and Objective tasks. Both VPC and DPC were more active for Subjective Remember compared to Objective Remember response. Neither PPC region was more active for remembering font and color compared to remembering only font or color. Memory load effects for retrieval of information from long-term memory were only seen in the hippocampus on the Subjective retrieval task. These patterns of activity support the role of the VPC in recollection, as seen on the Subjective task, and the role of the DPC in familiarity, as shown in both the Subjective and Objective tasks. The role of the VPC and DPC during recollection and familiarity processing supports both the AtoM and the EB model. The key predictor of the Episodic Buffer model, memory load effects, was not supported and provides the only evidence against one of the two proposed models. Future work should examine the role of the posterior parietal cortex in spontaneous episodic retrieval to assess the validity of the AtoM model. Advanced imaging analysis techniques should be used to determine functional connectivity between the PPC and frontal and temporal memory regions