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Connection, Connection, Connection…

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Science  01 Nov 2013:
Vol. 342, Issue 6158, pp. 577
DOI: 10.1126/science.342.6158.577

There are approximately 86 billion neurons in the human brain. Over the past decades, we have made enormous progress in understanding their molecular, genetic, and structural makeup as well as their function. However, the real power of the central nervous system lies in the smooth coordination of large numbers of neurons. Neurons are thus organized on many different scales, from small microcircuits and assemblies all the way to regional brain networks. To interact effectively on all these levels, neurons, nuclei, cortical columns, and larger areas need to be connected. The study of neuronal connectivity has expanded rapidly in past years. Large research groups have recently joined forces and formed consortia to tackle the difficult problems of how to experimentally investigate connections in the brain and how to analyze and make sense of the enormous amount of data that arises in the process.

This year's neuroscience special issue is devoted to general and also several more specific aspects of research on connectivity in the brain. We invited researchers to review the most recent progress in their fields and to provide us with an outlook on what the future may hold in store.

To make sense of larger structures, we first have to understand the composition of their basic building blocks. Markov et al. (p. 578) describe how interareal connectivity at the single-cell level, revealed by quantitative anatomical tract tracing, is relevant to our understanding of large-scale cortical networks and their hierarchical organization.

A different but also rapidly growing research direction deals with the use of connectivity measures to link brain structure and cognition. From the perspective of network theory, Park and Friston (p. 579) review our current understanding of structure-function relationships in large-scale brain networks and their underlying mechanisms.

One of the biggest breakthroughs in understanding the heavily connected brain has been the development of noninvasive brain-scanning methods, especially functional magnetic resonance imaging (fMRI). Turk-Browne (p. 580) provides an overview of recent exciting developments in large-scale fMRI data analysis, with a focus on unbiased approaches for examining whole-brain functional connectivity during cognitive tasks. Increased computational power now allows investigation of the whole-brain correlation matrix, the temporal correlation of every voxel with every other voxel throughout the brain, and the application of multivariate pattern analysis to these correlational data.

A sophisticated system that depends on the astonishingly precise interaction of a large number of cortical areas is the human ability to produce and understand language and music. Zatorre (p. 585) discusses how brain plasticity in the music and speech domains can be affected by predisposing factors that relate to brain structure and function.

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