Quantifying variability of Drosophila larva behavior under uni- and multi-sensory stimulation

The Drosophila larva is a small crawling animal that has a brain with about 10,000 neurons. To navigate their sensory environment, larvae execute computations that modify their behavioral outputs based on the temporal changes in their sensory inputs. When facing increases in aversive stimuli, such as light or CO₂, larvae on average respond by often changing their direction of movement. However, behavior of each larva can vary when subjected to the same stimulus presentation, and a larva may not respond with same fidelity to different sensory modalities. This intrinsic variability may reflect the differences in the neural implementation of their navigational algorithms to a range of sensory inputs. To study the larva’s information-processing algorithms, we stimulated their visual system with presentations of blue light and used red light presentations to optogenetically activate their CO₂ receptor neurons. By studying their responses to sensory stimuli alone and in combination, we categorize the variability of their behavioral responses to light and fictive odors and determine the conditions under which their combination provides a more reliable response to presentations of aversive stimuli. These approaches allowed us to hypothesize the basic underlying mechanisms that larvae engage in response to a combination of sensory cues.