Despite dense amnesia, patients with hippocampal lesions show partially intact navigation for recent and remotely learned environments

Abstract

The extent to which medial temporal lobe amnesia affects recently compared to remotely formed memories remains debated. Some studies have investigated this issue by employing either verbal recall of routes or map drawing, suggesting profound loss of recent yet largely intact remote spatial memory. Here, we studied navigation in two patients with amnesia and their matched controls by recreating virtual versions of their recent and remote neighborhoods. Both patients showed largely intact navigation of both their recent and remote neighborhoods, and, in most cases, navigated them better than a completely novel environment. Despite some intact navigation of these environments, patients showed dramatically reduced spontaneously cued episodic memories in these same environments compared to the controls. Our findings suggest that episodic memory and spatial navigation rely on partially distinct neural circuits, and support models of medial temporal lobe function in which extra-hippocampal networks are capable of supporting navigation in the absence of a functioning hippocampus.