In a very cool paper published yesterday in the open access journal PLoS Biology, an international team of researchers report that they have produced the most detailed and comprehensive map yet of the connections in the human cerebral cortex.
The cerebral cortex contains hundreds of billions of cells organized into thousands of discrete functional modules which act in parallel to generate all human behaviours and cognitive processes.
The new study uses neuroimaging to visualize more than 14,000 connections between nearly 1,000 of these modules, and reveals what the researchers call the brain’s structural core, which contains numerous connector hubs that link it to other areas throughout the brain.
Recent advances in neuroimaging technology have led to several new methods collectively known as diffusion imaging, which measure a signal generated by the movements of water molecules to visualize the white matter tracts, or bundles of nerve fibres that connect ditant regions of the brain.
In the new study, led by Olaf Sporns of the Computational Cognitive Neuroscience Laboratory at Indiana University, one of these new methods, called diffusion spectrum imaging, was used to analyse the brain’s so-called “connectome”, a map of large-scale connectivity within and between the two hemispheres of the brain, in more detail and at a higher resolution than ever before.
The data reveal that the brain contains a central core consisting of 8 distinct subregions in the posterior medial area of the cortex. This core radiates a dense network of fibres to other parts of the cortex, and may act as an integrated system which co-ordinates the combined activity of the two hemispheres.
The researchers then used fMRI to visualize the participants’ brains in the resting state. This showed that the central core region they had identified was more active than other regions, and so seems to be the brain’s “default” network.
fMRI is conventionally used to measure the relative levels of activity in a small number of brain modules. Such data are of limited usefulness if regarded on their own and not in the context of the functioning of the brain as a whole. Because the new study shows how a large number of these modules are interconnected, it should help researchers to better interpret functional neuroimaging data.
Hagmann, P. et al (2008). Mapping the Structural Core of Human Cerebral Cortex. PLoS Biology 6 (7), e159. [Full text]