Figure 4.

Olfactory circuits. (a) Top left: schematic of the principal paths of olfactory information flow in the D. melanogaster brain (outlined in grey), indicating the main neuron classes and brain regions. The circuitry is bilaterally symmetric (and most olfactory sensory neurons (OSNs) project to both antennal lobes) but only one hemibrain pathway is illustrated. Below are electron microscopic-resolution connectomic reconstructions of OSNs (including some antennal hygrosensory and thermosensory neurons [81–86]; contralateral innervations are cut off on the right side) and uniglomerular projection neurons (PNs) in the antennal lobe. Partner OSNs and PNs, converging on a common glomerulus, are colour-matched; one such glomerulus is highlighted in both images. For this PN class, a subset of the soma (located outside the lobe) are indicated with white arrowheads; black arrowheads point to the axons that project to the higher brain centres. (b) Connectomic reconstructions of the indicated neuronal populations. Data in (a,b) are adapted from [87], prepared by P. Schlegel; note that missing surface ‘strips’ in the middle of the antennal lobe are due to absent data.