All animals must find their way around their environment and home again. The ability to do this has been conserved across species and phyla and is an essential ability for survival. In mammals, this ability, referred to as navigation or wayfinding, is of two types: allocentric (spatial) and egocentric.
Allocentric navigation is the ability to wayfind using cues outside oneself and is known to be mediated primarily in the hippocampus. Egocentric navigation has received less attention but is impaired in a number of neurodegenerative and neuropsychiatric illnesses. Understanding it better may provide important insights into which brain regions are involved in neurological disorders.
Egocentric navigation is subdivided into two types: path integration and route-based wayfinding. Path integration involves vector addition, in which an organism can forage in multiple locations serially and return home by a novel, direct path never before taken. This process is akin to triangulation. Route learning involves using landmarks not as beacons to orientation of one’s position in space, but as signposts indicating nodes or junctions connecting segments of a path and, in the absence of signposts, can be accomplished in the dark using self-movement cues of distance combined with velocity.
We have developed a test of route learning called the Cincinnati Water Maze, in which rats learn to find their way through a complex maze without use of visual cues by testing them under infrared light. The lab is using neurotoxins to selectively ablate specific brain nuclei to map the circuitry underlying route-based navigation.