[in Japanese]

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Social learning is found in many animals, but its neural mechanisms remain unclear. We showed that a cricket that was trained to observe a conspecific staying at a drinking apparatus exhibited an increased preference for the odor of the drinking apparatus. We investigated a hypothesis that this learning is achieved by second-order conditioning (SOC), namely, crickets associate conspecifics at a drinking bottle with water reward during group-drinking at the rearing stage. Then they associate 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 suggests that reward-mediating octopamine neurons that respond to water during drinking are activated during observation of a conspecific staying at a drinking apparatus, and that such mirror-like activities of octopamine neurons mediate social learning. In observational fear learning in rodents, some cortical neurons that are activated when they receive pain are activated when they observe others responding to the pain, and such mirror-like activities are considered to help mediating observational fear response. We suggest that mirror-like activities mediate social learning in crickets, as is proposed in rodents.

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