Auditory circuit in the Drosophila brain.

Most animals exhibit innate auditory behaviors driven by genetically hardwired neural circuits. In Drosophila, acoustic information is relayed by Johnston organ neurons from the antenna to the antennal mechanosensory and motor center (AMMC) in the brain. Here, by using structural connectivity analysis, we identified five distinct types of auditory projection neurons (PNs) interconnecting the AMMC, inferior ventrolateral protocerebrum (IVLP), and ventrolateral protocerebrum (VLP) regions of the central brain. These auditory PNs are also functionally distinct; AMMC-B1a, AMMC-B1b, and AMMC-A2 neurons differ in their responses to sound (i.e., they are narrowly tuned or broadly tuned); one type of audioresponsive IVLP commissural PN connecting the two hemispheres is GABAergic; and one type of IVLP-VLP PN acts as a generalist responding to all tested audio frequencies. Our findings delineate an auditory processing pathway involving AMMC→IVLP→VLP in the Drosophila brain.