Posterior parietal cortex and episodic retrieval: convergent and divergent effects of attention and memory

Functional neuroimaging studies of humans engaged in retrieval from episodic memory have revealed a surprisingly consistent pattern of retrieval-related activity in lateral posterior parietal cortex (PPC). Given the well-established role of lateral PPC in subserving goal-directed and reflexive attention, it has been hypothesized that PPC activation during retrieval reflects the recruitment of parietal attention mechanisms during remembering. Here, we evaluate this hypothesis by considering the anatomical overlap of retrieval and attention effects in lateral PPC. We begin by briefly reviewing the literature implicating dorsal PPC in goal-directed attention and ventral PPC in reflexive attention. We then discuss the pattern of dorsal and ventral PPC activation during episodic retrieval, and conclude with consideration of the degree of anatomical convergence across the two domains. This assessment revealed that predominantly divergent subregions of lateral PPC are engaged during acts of episodic retrieval and during goal-directed and reflexive attention, suggesting that PPC retrieval effects reflect functionally distinct mechanisms from these forms of attention. Although attention must play a role in aspects of retrieval, the data reviewed here suggest that further investigation into the relationship between processes of attention and memory, as well as alternative accounts of PPC contributions to retrieval, is warranted.