Friday, September 30, 2011, 3pm
Innovation Hall room 136

Greg Stephens
Princeton University

More Bits for Behavior: Stochastic Dynamics in the Reversal Motions of C. elegans

Neither regular nor random, the dynamics of animal behavior are often riveting in observation. Indeed, characterizing the output motions of an entire organism is a substantial challenge in the physics of living systems. 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 and novel behaviors such as “pause” states at particular postures. We use the eigenworm projections to develop a stochastic model of the locomotor wave dynamics that predicts transitions between attractors corresponding to abrupt reversals in crawling direction. 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.