We imaged the complete brain of a female adult fruit fly at EM resolution. The resulting dataset comprises 21 million images occupying 106 TB. A cluster-backed image processing pipeline was developed to stitch, register, and intensity correct these images, enabling manual tracing of neuronal connectivity throughout the brain.
Pilot efforts have focused on the interface between the olfactory system and the mushroom body (MB), the site of associative learning. Each MB contains ~2,000 Kenyon cells (KCs), which receive olfactory input from the antennal lobe via second-order olfactory projection neurons (PNs) in the MB calyx, in what is thought to be a random fashion. KC axons then form a bundle called the pedunculus, which gives rise to the lobes of the mushroom body, where synaptic modulation underlying memory occurs. We traced about 10% of the KCs in the calyx, and their presynaptic PN inputs, to generate a PN-to-KC connectivity graph. We find that KCs that fasciculate with one another in the pedunculus are much more likely to receive input from a common PN, and are also more likely to make axo-axonic synapses with one another. This network structure might be used to sharpen and amplify olfactory signals prior to their arrival in the MB lobes, where synapses are modified during associative Learning.