A circuit library for exploring the functional logic of massive feedback loops in Drosophila brain

The functional logic of brain circuits of Drosophila neuropils is largely determined by local/intrinsic neurons. The architecture of the antennal lobe (AL), for example, is numerically dominated by its local neurons (LNs) that interact with olfactory sensory neurons (OSNs) and projection neurons (PNs) within and across glomeruli. Detailed connectomic data, e.g., the Hemibrain dataset, reveal a massive number of nested feedback loops among these three classes of neurons. Dissecting the role of these feedback circuits is key to the understanding the computation taking place in AL and beyond. However, there has been little systematic study of the functional role of these feedback loops in the brain of the fruit fly. In order to explore the functional logic of the feedback loops in the fruit fly brain, we developed a circuit library that brings together the available Drosophila connectomic, synaptomic and cell type data, with tools for 1) querying connectome datasets that automatically find and incorporate feedback pathways, 2) generation of interactive circuit diagrams of the feedback circuits, 3) automatic derivation of executable models based on feedback circuit abstractions anchored on actual connectomic data, 4) arbitrary manipulation (and/or ablation) of feedback circuits on the interactive circuit diagram for execution, and 5) systematic characterization and comparison of the effect of different feedback circuits on the I/O relationship. We demonstrate the capabilities of the library using circuits of the DM4 and DL5 glomeruli of the Drosophila antennal lobe constructed either individually or together, from the Hemibrain dataset. We characterize the contribution of individual feedback motifs as well as their compositions on the circuit.