Connectome

A connectome is a comprehensive map of neural connections within an organism’s nervous system. It encompasses the wiring between individual neurons, including synapses and gap junctions, or the connections between brain regions linked by white matter tracts. The goal of connectomics is to reconstruct the wiring diagram that underlies brain function and behavior. A structural connectome maps physical connections, while a functional connectome describes statistical dependencies between neural elements, often derived from time-series data.

A notable example is the complete connectome of the nematode Caenorhabditis elegans, published in the late 20th century, which mapped all 302 neurons and their roughly 7,000 synapses. In humans, a complete connectome remains beyond current capabilities; researchers pursue partial or approximate maps at cellular, regional, and network scales. Structural connectomes rely on diffusion MRI and tractography to infer white-matter pathways, whereas functional connectomes use functional imaging methods such as fMRI, EEG, or MEG to estimate connectivity patterns. At the cellular level, electron microscopy and serial section imaging are used to reconstruct synapses in smaller brains or targeted regions.

Connectomics employs graph theory and network science: nodes represent neurons or brain regions, and edges represent synapses, fiber tracts, or statistical associations. Projects such as the Human Connectome Project and other large-scale data initiatives advance data collection, standardization, and analysis. The term connectome was popularized in the mid-2000s by researchers including Sporns, Tononi, and Kötter, and the broader field seeks to relate network structure to function, development, and disease. Challenges include data scale, variability across individuals, and accounting for dynamic plasticity.

Understanding the connectome offers potential insights for neuroscience, medicine, and brain-inspired computing, but current maps remain incomplete and provisional.