Mechanosensory Representations in the Drosophila Brain

Abstract

Johnston’s organ is the largest mechanosensory organ in Drosophila. It contributes to hearing, touch, vestibular sensing, proprioception, and wind sensing. In the first part of this study, we used in vivo 2-photon calcium imaging and unsupervised image segmentation to map the tuning properties of Johnston’s organ neurons (JONs) at the site where their axons enter the brain. We then applied the same methodology to study two key brain regions that process signals from JONs: the antennal mechanosensory and motor center (AMMC) and the wedge, which is downstream of the AMMC. We found that, whereas JONs form a rough tonotopic map, the AMMC and wedge contain progressively finer and more orderly tonotopic maps. Whereas the AMMC tonotopic map is unilateral, the wedge tonotopic map is bilateral. We also observed the emergence of bilaterality in the regions of the AMMC and wedge that respond preferentially to steady wind. Together, these maps reveal the broad organization of the primary and secondary mechanosensory regions of the brain. They provide a framework for future efforts to identify the specific cell types and mechanisms that underlie the hierarchical re-mapping of mechanosensory information in this system. In the second part of this study, we examined how information about wind direction, which is transduced through JONs, influences the brain’s heading direction “compass” in the central complex. We identified neurons that provide input to the central complex from the brain’s mechanosensory regions. We also showed that these neurons have properties which should allow them to encode wind direction in a manner which is robust to wind intensity.