Abstract Serotonin (5-HT) is a hormonal messenger that confers state-level changes upon the nervous system in both humans and flies. In Drosophila, lobula columnar (LC) cells are feature-detecting neurons that project from the optic lobe to the central brain, where each population forms an anatomically-distinct glomerulus with heterogeneous synaptic partners. Here, we investigated serotonin's effect on two LC populations with different 5-HT receptor expression profiles.