Summary
Mapping the complete wiring diagram of neural connections, as achieved for the C. elegans nervous system.
In depth
Electron microscopy reconstructions give complete wiring: C. elegans (302 neurons, about 7,000 connections), the fly hemibrain and fragments of mouse and human cortex. Challenges: huge data and analysing function.
Connectomes reveal circuit motifs. Large-scale reconstruction uses machine learning. Structure alone does not tell function.
Example: the fruit fly connectome was completed in 2023-2024 for the whole brain.
A connectome is a complete map of neural connections. C. elegans was mapped by hand in 1986 (White et al.) and is the only complete adult connectome of an animal until recently, followed by the larval fly and the adult fly (FlyWire, about 130,000 neurons and 50 million synapses, 2024) and a cubic millimetre of mouse cortex (MICrONS, 2025) and human cortex (Google and Harvard, 2024, a fragment with about 57,000 cells and 150 million synapses). Methods: serial section electron microscopy, automated segmentation by machine learning, and expansion microscopy.
Macroscale connectomes, from diffusion MRI (Human Connectome Project), map tracts between regions. Connectomes reveal wiring motifs and hubs, but not synaptic strength or neurotransmitter, and are static. The challenge is to get from wiring to function.
Key idea: the structure of connections limits and shapes the computations that a nervous system can perform.
Frequently asked questions
What is Connectomics?
Mapping the complete wiring diagram of neural connections, as achieved for the C. elegans nervous system.
Which area of biology covers Connectomics, and how advanced is it?
Connectomics is one of the 54 topics in Neuroscience. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Computational Neuroscience, Brain Imaging, Nervous System.
Can you give an example of Connectomics?
The MICrONS project reconstructed a cubic millimetre of mouse cortex.
What should I learn before Connectomics?
Work through the Beginner topics in Neuroscience first, such as Nervous System, Neuron, Central and Peripheral Nervous Systems, then return to Connectomics. Advanced topics assume the Intermediate vocabulary.
What topics are related to Connectomics?
The closest topics to Connectomics are Computational Neuroscience, Brain Imaging, Nervous System, Visual Cortex Processing. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Connectomics?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Connectomics. To practise the whole of Neuroscience, use the Neuroscience quiz.
How is Connectomics different from Computational Neuroscience?
Connectomics: Mapping the complete wiring diagram of neural connections, as achieved for the C. elegans nervous system. Computational Neuroscience: Uses mathematical and computer models to explain how neurons and networks process information. Read both side by side and note what each one explains.
How should I study Connectomics step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Computational Neuroscience and explain the difference aloud. Finally, take the Neuroscience quiz and come back to this page for any question you miss.