A bat's perspective on navigation

Abstract

Much has been learned during the past decades about how animals navigate in their local environment. We know that most taxonomic groups, from arthropods to mammals, use multiple mechanisms to find their way (1). Animals may reach goals by following trails or approaching salient beacons or by computationally more sophisticated strategies, such as path integration (1, 2) and the use of geometric “cognitive maps” of the external environment (3, 4). The mammalian brain has specialized systems for many of these functions. Key components include, in the hippocampus, place cells, which are cells that fire only when the animal is in specific positions (4, 5), and, in the entorhinal cortex, grid cells, which provide the animal with a universally applicable metric of local space (5, 6). Together with direction-coding cells (7), place and grid cells are known to form a map-like neural representation of the animal's external environment (4–6). Despite these emerging insights, the growing knowledge of how space is computed in the mammalian brain is based almost exclusively on small-scale laboratory studies in which rodents forage in a test box or on a track. Whether similar mechanisms are used during large-scale navigation in the animal's natural habitat remains to be determined. Most of our knowledge about long-distance navigation comes from studies of nonmammalian species, such as birds, insects, fish, and sea turtles. Those studies have identified sources of information used by animals to determine compass direction as well as spatial location, for example the geomagnetic field, olfactory gradients, and celestial cues such as the sun and the stars (1, 8–11). The physiological mechanisms used to extract the information are not well understood, however, and the relationship to local spatial representation mechanisms described in mammals has almost not been examined at all.