Insect brain plasticity: effects of olfactory input on neuropil size

Insect brains are known to express a high degree of experience-dependent structural plasticity. One brain structure in particular, the mushroom body, has been attended to in numerous studies as it is implicated in complex cognitive processes such as olfactory learning and memory. It is, however, poorly understood to what extent sensory input per se affects plasticity of the mushroom bodies. By performing unilateral blocking of olfactory input on immobilized butterflies, we were able to measure the effect of passive sensory input on the volumes of antennal lobes and mushroom body calyces. We showed that the primary and secondary olfactory neuropils respond in different ways to olfactory input. Antennal lobes show absolute experience-dependency and increase in volume only if receiving direct olfactory input from ipsilateral antennae, while mushroom body calyx volumes were unaffected by the treatment and instead show absolute age-dependency in this regard. We therefore propose that cogniti...