Statistical discrimination of natural modes of motion in rat exploratory behavior

We analyze the locomotor behavior of the rat during exploration, and show that digitally collected data (time series of positions) provide a sufficient basis for establishing that the rat uses several distinct modes of motion (first, second, third, and sometimes fourth gear). The distinction between these modes is obtained by first segmenting the time series into sequences of data points occurring between arrests (as ascertained within the resolution of the data acquisition system). The statistical distribution of the maximal amount of motion occurring within each of these episodes is then analyzed and shown to be multi modal. This enables us to decompose motion into distinct modes. In one application of this decomposition we show that the ethological ad hoc notion of stopping behavior corresponds to progression without leaving first gear. We do so by showing that the spatial spread of such progressions is confined to a small 20-50 cm range in a 6.5 m diameter arena. This provides a justification for a construct of 'staying in place'. This construct is not defined in terms of position in objective space, but purely in terms of the rat's own behavior. We test the generality of our method by applying it to mouse exploratory behavior.