Hemibrain

Hemibrain is a publicly accessible electron microscopy–based connectome of the Drosophila melanogaster brain, representing roughly one hemisphere of the adult fruit fly’s central nervous system. It is produced by the FlyEM project at Janelia Research Campus (and collaborators) and combines high-resolution serial-section EM imaging with automated segmentation and extensive manual proofreading to reconstruct neuronal morphologies and synaptic connections. The dataset aims to provide a scalable, reference-quality map of neural wiring in the fly brain.

The hemibrain dataset encompasses tens of thousands of neurons and tens of millions of synapses, spanning major brain regions such as the mushroom body, central complex, antennal lobe, and optic neuropil. It supports inquiry into circuit motifs, information flow, and connectivity patterns that underlie sensory processing, learning, and behavior in Drosophila. Annotations include neuron identities and classifications, anatomical regions, and synaptic contacts, enabling researchers to examine specific pathways and network properties.

Access and tools are provided through neuPrint, a data portal and API that enables neuron-centric and synapse-centric queries. Users can explore connectivity between neuron types (for example, projection neurons, Kenyon cells, MBONs), examine synaptic weights, and visualize circuits within chosen neuropils. Hemibrain has undergone multiple releases as reconstructions are refined and expanded, incorporating corrections and additional neurons over time.

As a partial (hemispheric) brain map, hemibrain is often used in conjunction with other datasets to inform whole-brain inferences. It serves as a foundational resource for structural connectomics, circuit mapping, and computational modeling in Drosophila, supporting investigations into memory, navigation, neuromodulation, and other brain functions.