A big question in biology is how to understand complex animal behavior. We want to know why it happens, how it happens, what are predictors of those behaviors. Caenorhabditis elegans is an excellent animal model for studying behavior because its movements can be simplified and described in four discrete dimensions or “eigenworms”. (See figure 1 below.) In a recent paper , the laboratory of Dr. William Bialek characterizes the stereotyped worm movements using a computational model.
The figure above illustrates how you get from a worm crawling on a plate to a computational model of motor behavior in C. elegans .
The Bialek lab addresses the difference between two common models for behavior: 1) Stereotyped motor behaviors can be directly attributed to certain “command neurons” firing action potentials, and the activity of single neurons determines the stereotypy. 2) In contrast, these motor behaviors exhibit stereotypy due to the dynamics of the neuronal circuit as a whole.
These models can be applied to specific worm movements, reversals, in which the worm switches from moving forward to moving backwards, or vice versa. The reversals correlate with time spent away from a food source, so that when a long amount of time passes without food, the worm will continue moving in one direction and change its direction less often.
The figure above displays experimental data (A) compared to simulated data (B) to show that the stochastic model can reliably predict motor behavior in C. elegans .
The Bialek lab models the worm movements as a stochastic dynamical system that features noise as the drive for reversals. They found that increasing length of time away from food decreases the amplitude of noise. This finding suggests that noise within the neuronal circuit can be used to modify motor behavior in C. elegans.
The work in the laboratory of Dr. William Bialek at Princeton University centers on merging biology and physics.
Please join us on Tuesday December 18th at 4pm in Leichtag 107 (note location change) for Dr. Bialek’s presentation on modeling the motor movements of C. elegans using a stochastic dynamical system.
Melissa Galinato is a first year in the UCSD Neurosciences Graduate Program. Melissa is currently finishing her first rotation in the laboratory of Dr. Chitra Mandyam, studying adult hippocampal neurogenesis at The Scripps Research Institute.
Stephens G.J., Bueno de Mesquita M., Ryu W.S. & Bialek W. (2011). Emergence of long timescales and stereotyped behaviors in Caenorhabditis elegans, Proceedings of the National Academy of Sciences, 108 (18) 7286-7289. DOI: 10.1073/pnas.1007868108