Colloquium: Greg Stephens
M623, De Boeleaan 1081, Vrije Universiteit, Amsterdam
More bits for behavior: Stochastic dynamics in the reversal motions of C. elegans
Greg Stephens, Princeton Uniersity
Faculty of Sciences
From the dynamics of single molecules to networks of gene expression, there has been an explosion in our ability to measure the microscopic components of living systems. The output behavior of an entire organism, however, is often still characterized by eye. Here we use high resolution video microscopy to record the motions of the nematode C. elegans, freely-wiggling on a flat agar plate. We show that the space of shapes is remarkably low dimensional, with just four dimensions accounting for 95% of the shape variance. Projections of worm shape along these four “eigenworms” provide a precise yet substantially complete description of worm behavior, capturing both classical worm motion such as forward crawling, reversals, and Ω-turns and novel behaviors such as “pause” states at particular postures. We use the eigenworm projections to develop a stochastic model of the worm's locomotor wave dynamics that predicts transitions between attractors corresponding to abrupt reversals in crawling direction.
With no free parameters, our inferred dynamical system generates long reversal time scales and stereotyped trajectories in close agreement to experimental observations. Finally, we use our stochastic model to demonstrate that the noise amplitude decreases systematically with increasing time away from food, resulting in longer bouts of forward crawling and suggesting that worms use noise to adaptive benefit.