Multimodal dissociation of posterior cingulate cortex contributions to episodic memory

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Project Summary Episodic memory is the ability to recall details about prior experiences. Researchers have historically relied on controlled item-recognition paradigms, in complement to autobiographical recall tasks, to investigate the biological substrates of episodic memory. Contemporary theories posit that episodic memory is supported by a constellation of neocortical regions, in concert with the hippocampus and medial temporal cortices. Of these neocortical regions, the posterior cingulate cortex (PCC) stands out because it is reliably observed in neuroimaging studies of episodic memory and demonstrates engagement that is sensitive to memory strength. Although a large literature indicates that the PCC is critical for episodic memory, very little is known about its unique role in memory or cognition more broadly. Meta-analyses of functional neuroimaging studies that have investigated the relationship between memory tasks and PCC activations provide some insight as to the region’s role. Strikingly, while item-recognition tasks are associated with activity in the dorsal subregion of the PCC (dPCC), autobiographic recall tasks are uniquely associated with activity in the ventral PCC subregion (vPCC). This functional divide mirrors similar cytoarchitectural and network-connectivity differences found along the dorsal-ventral axis of the PCC. Furthermore, the dPCC is consistently implicated in decision-making studies, while the vPCC has been found to be involved in the representation of specific features and semantic associations of retrieved memories. Synthesizing across previous observations suggests that the dPCC serves as a putative accumulator of mnemonic evidence during memory-based decisions, while the vPCC serves to support the retrieval of details about previous episodes. However, progress in clarifying the contributions of PCC subregions to episodic memory have been stymied due to the location of the region within the medial surface, making it challenging to isolate the dynamics of PCC signals using traditional electrophysiological recording and neuroimaging methods. The use of cutting-edge techniques can help overcome previous limitations in spatiotemporal precision that have prevented advances in understanding the function of the PCC: high-resolution functional neuroimaging and invasive electrophysiological recordings of population and single neuron activity. An openly-available, high-resolution neuroimaging dataset containing thousands of item-recognition trials per participant will be used to isolate the functional organization of item-recognition response patterns in the PCC. Population responses collected via intracranial electrodes will be analyzed in order to temporally isolate tightly coupled memory-decision and memory-retrieval processes across the PCC. Additionally, single unit recordings from the PCC will be collected and used to test whether memory-selective and visual-selective units can be identified in the PCC, underlying population level signals observed in response to memory decisions and retrieval. Results from this work will provide a significant advance to our understanding of functional organization in the PCC, helping map the ways memory deficits can progress in healthy aging and disease.