Handedness and individuality in free-crawling vermiforms

We deploy two of the simplest model organisms, studying one of their simplest behaviors, to better understand internal states of individual animals and how internal states affect sensory processing and behavior. Both the fruit fly Drosophila larva and the nematode C. elegans crawl almost continuously on flat surfaces, in patterns akin to the classic random walk. We focus on the right/left outcome of their turning events and drifting, tracking many individuals during free exploration, and during navigation in thermal or chemical gradients.

We find a wide distribution of turn and drift direction bias ("handedness") that is statistically significant in both organisms but persists weakly over longer time scales. For larvae, we can continuously record movement over 6+ hours, aided by an automated transport robot, and characterize changes in handedness over time.

We also investigate what happens when turn-biased individuals encounter stimuli that normally elicit turns opposing the individual bias, finding that internal preference often overrides the external influence.

These results suggest that this simple behavior in these organisms can provide a window into more complex interactions between internal preference and external signals in the brain.