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 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. ==Plasticity of the connectome== At the beginning of the connectome project, it was thought that the connections between neurons were unchangeable once established and that only individual synapses could be altered. However, recent evidence suggests that connectivity is also subject to change, termed neuroplasticity. There are two ways that the brain can rewire: formation and removal of synapses in an established connection or formation or removal of entire connections between neurons. Both mechanisms of rewiring are useful for learning completely novel tasks that may require entirely new connections between regions of the brain. However, the ability of the brain to gain or lose entire connections poses an issue for mapping a universal species connectome. Although rewiring happens on different scales, from microscale to macroscale, each scale does not occur in isolation. For example, in the C. elegans connectome, the total number of synapses increases 5-fold from birth to adulthood, changing both local and global network properties. Other developmental connectomes, such as the muscle connectome, retain some global network properties even though the number of synapses decreases by 10-fold in early postnatal life. ==Origin and usage of the term== In 2005, Dr. Olaf Sporns at Indiana University and Dr. Patric Hagmann at Lausanne University Hospital independently and simultaneously suggested the term "connectome" 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. "Connectomics" has been defined as the science concerned with assembling and analyzing connectome data sets. In their 2005 paper, "The Human Connectome, a structural description of the human brain", Sporns et al. wrote: To understand the functioning of a network, one must know its elements and their interconnections. The purpose of this article is to discuss research strategies aimed at a comprehensive structural description of the network of elements and connections forming the human brain. We propose to call this dataset the human "connectome," and we argue that it is fundamentally important in cognitive neuroscience and neuropsychology. The connectome will significantly increase our understanding of how functional brain states emerge from their underlying structural substrate, and will provide new mechanistic insights into how brain function is affected if this structural substrate is disrupted. In his 2005 Ph.D. thesis, From diffusion MRI to brain connectomics, Hagmann wrote: It is clear that, like the genome, which is much more than just a juxtaposition of genes, the set of all neuronal connections in the brain is much more than the sum of their individual components. The genome is an entity it-self, as it is from the subtle gene interaction that [life] emerges. In a similar manner, one could consider the brain connectome, set of all neuronal connections, as one single entity, thus emphasizing the fact that the huge brain neuronal communication capacity and computational power critically relies on this subtle and incredibly complex connectivity architecture. The term "connectome" was more recently popularized by Sebastian Seung's I am my Connectome speech given at the 2010 TED conference, which discusses the high-level goals of mapping the human connectome, as well as ongoing efforts to build a three-dimensional neural map of brain tissue at the microscale. In 2012, Seung published the book Connectome: How the Brain's Wiring Makes Us Who We Are. TED talk by Sebastian Seung: "I am my connectome". braingraph.org: a database of hundreds of braingraphs, computed from the data of the Human Connectome Project

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