Octopamine neurons mediate reward signals in social learning in an insect.

Social learning is found in many animals, but its mechanisms are not understood. We previously showed that a cricket that was trained to observe a conspecific staying at a drinking apparatus exhibited an increased preference for the odor of that drinking apparatus. Here we investigated a hypothesis that this learning is achieved by second-order conditioning (SOC), i.e., by associating conspecifics at a drinking bottle with water reward during group drinking in the rearing stage and then associating an odor with a conspecific in training. Injection of an octopamine receptor antagonist before training or testing impaired the learning or response to the learned odor, as we reported for SOC, thereby supporting the hypothesis. Notably, the SOC hypothesis predicts that octopamine neurons that respond to water in the group-rearing stage also respond to a conspecific in training, without the learner itself drinking water, and such mirror-like activities mediate social learning. This awaits future investigation.