Embodied behavioural complexity in a ciliated microorganism

Most animals coordinate behavior using neural computations. Yet, single-celled organisms also exhibit stimulus-responsive, even cognitive, actions. To understand how a single cell can coordinate and drive complex behaviors without any neural encoding, we study an algal protist -- a motile cell with four extremely long cilia. The organism displays a surprisingly rich locomotor repertoire, emerging from the intricate dynamics of the cilia, which form a tight bundle when swimming.

By combining high-speed quantitative live imaging with spectral mode decomposition and wavelet analysis, we extract the spectrum of possible ciliary beating patterns, and derive a dispersion relation coupling the temporal frequency and spatial wavelength of cilia oscillations. In addition, we reconstruct a low-dimensional manifold embedded in the behavioral space, showing that despite the range and complexity of ciliary beating modes, the underlying behavioral manifold is intrinsically low-dimensional with dynamic and excitable transitions in motility behavior encoded as trajectories in this space.