Connectome

A connectome (/kəˈnɛktoʊm/) is a comprehensive map of neural connections in the brain, and may be thought of as its "wiring diagram".^[2] These maps are available in varying levels of detail. A functional connectome shows connections between various brain regions, but not individual neurons. These are available for large animals, including mice and humans, are normally obtained by techniques such as MRI, and have a scale of millimeters. At the other extreme are neural connectomes, which show individual neurons and their interconnections. These are usually obtained by electron microscopy and have a scale of nanometers. They are only available for small creatures such as the worm C. Elegans and the fruit fly Drosophila melanogaster, and small regions of mammal brains. Finally there are chemical connectomes, showing which neurons emit, and are sensitive to, a wide variety of neuromodulators.

The significance of the connectome stems from the realization that the structure and function of any brain are intricately linked, through multiple levels and modes of brain connectivity. There are strong natural constraints on which neurons or neural populations can interact, or how strong or direct their interactions are. Indeed, the foundation of human cognition lies in the pattern of dynamic interactions shaped by the connectome.

Despite such complex and variable structure-function mappings, connectomes are an indispensable basis for the mechanistic interpretation of dynamic brain data, from single-cell recordings to functional neuroimaging.

The terms connectome and connectomics were introduced independently by Olaf Sporns at Indiana University and Patric Hagmann at Lausanne University Hospital to refer to a map of the neural connections within the brain. This term was directly inspired by the ongoing effort to sequence the human genetic code—to build a genome. It was more recently popularized by Sebastian Seung's I am my Connectome speech given at the 2010 TED conference.^[3] In 2012, Seung published the book Connectome: How the Brain's Wiring Makes Us Who We Are.