Illumination mediates a switch in both active sensing and control in weakly electric fish

Animals integrate multiple sensory inputs to explore environments and execute locomotor behaviors. To carry out these behaviors, the nervous system internally reweights controller gains, putting more emphasis on those with the least uncertainty, e.g. in a Bayesian framework. Meanwhile, as sensory uncertainty increases, animals produce more vigorous active sensing movements. To better understand the link between these two complementary processes—multisensory reweighting and active sensing—we studied how the weakly electric glass knifefish Eigenmannia virescens alters its movement dynamics under parametric manipulations of illumination. We hypothesized a concomitant switch in both active sensing (an overt behavior) and multisensory reweighting (an internal control computation). To test this, we varied illumination levels from 0.1 to 210 lx as fish tracked a moving refuge. We discovered that in a neighborhood of a critical threshold (on the order of 1 to 10 lx), small increases in illumination led to dramatic changes in both active sensing and multisensory control, specifically in 1) steep reductions in fish head and tail movements and 2) decreased refuge tracking phase lag. Outside of this threshold, large changes in illumination only caused mild changes in behavior. A control-theoretic model that dynamically modulates the weights of vision and electrosense due to illumination changes explains the changes in closed-loop behavior in our experiments. Our findings enhance our understanding of active sensing, multisensory reweighting, and locomotor control.