Relationship between the phases of sensory and motor activity during a looming-evoked multistage escape behavior.

The firing patterns of visual neurons tracking approaching objects need to be translated into appropriate motor activation sequences to generate escape behaviors. Locusts possess an identified neuron highly sensitive to approaching objects (looming stimuli), thought to play an important role in collision avoidance through its motor projections. To study how the activity of this neuron relates to escape behaviors, we monitored jumps evoked by looming stimuli in freely behaving animals. By comparing electrophysiological and high-speed video recordings, we found that the initial preparatory phase of jumps occurs on average during the rising phase of the firing rate of the looming-sensitive neuron. The coactivation period of leg flexors and extensors, which is used to store the energy required for the jump, coincides with the timing of the peak firing rate of the neuron. The final preparatory phase occurs after the peak and takeoff happens when the firing rate of the looming-sensitive neuron has decayed to <10% of its peak. Both the initial and the final preparatory phases and takeoff are triggered when the approaching object crosses successive threshold angular sizes on the animal's retina. Our results therefore suggest that distinct phases of the firing patterns of individual sensory neurons may actively contribute to distinct phases of complex, multistage motor behaviors.