Statistical discrimination of natural modes of motion in rat exploratory behavior

We analyze the locomotor behavior of the rat during exploration, and show t hat digitally collected data (time series of positions) provide a sufftcien t 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 resolu tion of the data acquisition system). The statistical distribution of the m aximal amount of motion occurring within each of these episodes is then ana lyzed 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 w ithout leaving first gear. We do so by showing that the spatial spread of s uch 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 m ethod by applying it to mouse exploratory behavior. (C) 2000 Elsevier Scien ce B.V. All rights reserved.