Map reading, navigating from maps, and the medial temporal lobe

Abstract

We administered map-reading tasks in which participants navigated an array of marks on the floor by following paths on hand-held maps that made up to nine turns. The burden on memory was minimal because the map was always available. Nevertheless, because the map was held in a fixed position in relation to the body, spatial computations were continually needed to transform map coordinates into geographical coordinates as participants followed the maps. Patients with lesions limited to the hippocampus (n = 5) performed similar to controls at all path lengths (experiment 1). They were also intact at executing single moves to an adjacent location, even when trials began by facing in a direction that put the map coordinates and geographical coordinates into conflict (experiment 2). By contrast, one patient with large medial temporal lobe (MTL) lesions performed poorly overall in experiment 1 and poorly in experiment 2 when trials began by facing in the direction that placed themap coordinates and geographical coordinates in maximal conflict. Directly after testing, all patients were impaired at remembering factual details about the task. The findings suggest that the hippocampus is not needed to carry out the spatial computations needed formap reading and navigating from maps. The impairment in map reading associated with large MTL lesions may depend on damage in or near the parahippocampal cortex.