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In neuroscience, two basic principles guide our understanding of brain disease: either mental illness is a result of lesions of discrete areas devoted to performing specific mental operations or the locus of pathology lies
within the pattern of connections among different brain regions. These two approaches are known, respectively, as segregationist and integrationist views.
Over the last century, accounts of pathology have almost exclusively relied on the segregationist perspective, given the explanatory power of this approach as exemplified by the cases of Broca's aphasia and Parkinson's disease. This predominance has also been the result of technical limitations, in that the investigative tools available until recently allowed the examination of only a limited number of brain areas.
With the advent of MRI and, more recently, of faster computational tools, scientists have begun to focus more on connections among brain areas, accumulating empirical support for a more integrationist approach to psychopathology. The NIH has spearheaded such efforts with what is known as the Human Connectome Project (HCP) ().
Just as the Human Genome Project (HGP) aimed at mapping the entire human genome, the HCP aims at describing the connectome, a comprehensive map specifying the anatomical and functional connections among all regions in the brain, as well as the organizational principles that govern them. The HCP uses a variety of imaging techniques that have given rise to the field of “imaging connectomics.”
How does one go about examining brain connections? Scientists can map white matter tracts, which are the “highways” of axonal fibers connecting different regions of the brain. This type of connectivity is called anatomical connectivity, and it employs imaging methods such as Diffusion Weighted Imaging (DWI). Another approach examines how neurophysiological signals in different areas of the brain vary together over time. The st