Connectomics

Connectomics is the production and study of connectomes, which are comprehensive maps of connections within an organism's nervous system. Study of neuronal wiring diagrams looks at how they contribute to the health and behavior of an organism. There are two very different types of connectomes; microscale and macroscale. Microscale connectomics maps every neuron and synapse in an organism or chunk of tissue, typically using electron microscopy and histology. This level of detail is only possible for small animals (flies and worms) or tiny portions (less than 1 mm on a side) of large animal brains. Macroscale connectomics, on the other hand, refers to mapping out large fiber tracts and functional gray matter areas within a much larger brain (typically human), typically using forms of MRI to map out structure and function. Both fields simply refer to their maps as "connectomes". Macroscale connectomics typically concentrates on the human nervous system, a network made of up to billions of connections and responsible for our thoughts, emotions, actions, memories, function and dysfunction. Because these structures are physically large and experiments on humans are routinely non-invasive, typical methods are functional and structural MRI data to measure blood flow (functional) and water diffusivity (structural). Examples include the Human Connectome Project and others. Connectomics in this regime aims to advance our understanding of mental health and cognition by understanding how cells in the nervous system are connected and communicate. In contrast, microscale connectomics looks in much greater detail at much smaller circuits. In very small animals such as the worm C. elegans or the fruit fly Drosophila, the entire nervous system can be reconstructed. In the much larger mammal brains, studies examine subregions such as the retina and cortex. Connectomics at these scales searches for mechanistic explanations of how the nervous system operates.