Two parallel pathways convey distinct visual information to the Drosophila mushroom body

ABSTRACT The ability to integrate input from different sensory systems is a fundamental property of many brains. Yet, the patterns of neuronal connectivity that underlie such multisensory integration remain poorly characterized. The Drosophila mushroom body — an associative center required for the formation of olfactory and visual memories — is an ideal system to investigate how neurons of different sensory channels converge in higher-order brain centers. The neurons connecting the mushroom body to the olfactory system have been described in great detail in Drosophila melanogaster, but input from other sensory systems remains poorly defined. Here, we used a range of anatomical and genetic techniques to identify two novel types of mushroom body input neuron that connect a processing center — the lobula— to the dorsal accessory calyx of the mushroom body. Together with previous work showing that the ventral accessory calyx of the mushroom body receives input from another visual processing center, the medulla (Vogt et al., 2016) our results define a second, parallel pathway that conveys visual information to the mushroom body. This connectivity pattern could be a fundamental feature of the neuronal architecture underlying multisensory integration in associative brain centers.