A phase plane representation of rat exploratory behavior.

Rat spontaneous spatial behavior is considered to be stochastic and is therefore commonly analyzed in terms of cumulative measures. Here, we suggest a method which generates a moment-to-moment representation of this behavior. It has been proposed earlier that rat spatial behavior can be partitioned into natural units termed excursions (round trips) performed from a reference place termed the rat's home base. We offer a phase plane representation of excursions (plotting the rat's momentary location against its momentary velocity). The results reveal a geometrical pattern, typical of young age and early exposure. It consists of low velocity and intermittent progression while moving away from the home base (upstream segment), and high velocity while moving back to it (downstream segment). The asymmetry between the two segments defines a field of significance in the rat's operational world. This field undergoes regular transformations, revealing thereby the rat's strategy of occupancy of the environment. The presented dynamics could provide a framework for the interpretation of concurrent neural events associated with navigation and spatial memory.