The first high-resolution map showing how millions of neural fibres connect and communicate in the human cerebral cortex has been achieved, an international team of scientists have claimed. The cortex is the outer layer of the brain responsible for higher-level thinking.
The researchers say that their study marks a major step in understanding the most complicated and mysterious organ in the human body, and identifies a single network core that may be key to the working of both hemispheres of the brain.
They say that their work also describes a novel application of a non-invasive technique that can be used by other scientists to continue mapping the trillions of neural connections in the brain at even greater resolution, which is becoming a new field of science termed "connectomics".
"This is one of the first steps necessary for building large-scale computational models of the human brain to help us understand processes that are difficult to observe, such as disease states and recovery processes to injuries," said Olaf Sporns, a neuroscientist at Indiana University.
Writing about their findings in the journal PLoS Biology, the researchers say that scientists mostly use functional magnetic resonance imaging (fMRI) technology to measure brain activity, which helps them locate which parts of the brain become active during perception and cognition.
However, the researchers add, there has been little understanding of the role of the underlying anatomy in generating this activity.
The researchers also point out that neural fibre connections and pathways have largely been studied in animals to date, but no one ever came up with a complete map of such connections in the human brain.
In their latest study, neuroimaging researchers led Patric Hagmann of University Hospital Center and University of Lausanne used state-of-the-art diffusion MRI technology, a non-invasive scanning technique that estimates fibre connection trajectories based on gradient maps of the diffusion of water molecules through brain tissue.
The researchers say that a highly sensitive variant of the method, called diffusion spectrum imaging (DSI), can depict the orientation of multiple fibers that cross a single location.
During the study, they applied the technique to the entire human cortex, resulting in maps of millions of neural fibers running throughout this highly furrowed part of the brain.
Sporns later conducted a computational analysis to locate brain regions that played a more central role in the connectivity, serving as hubs in the cortical network.
His efforts unveiled a single highly and densely connected structural core in the brain of all participants.
"We found that the core, the most central part of the brain, is in the medial posterior portion of the cortex, and it straddles both hemispheres. This wasn't known before. Researchers have been interested in this part of the brain for other reasons. For example, when you're at rest, this area uses up a lot of metabolic energy, but until now it hasn't been clear why," he said.
He revealed that the research team later wanted to known ether the structural connections of the brain in fact shape its dynamic activity, and thus examined the brains of five human participants who were imaged using both fMRI and DSI techniques to compare how closely the brain activity observed in the fMRI mapped to the underlying fibre networks.
"It turns out they're quite closely related. We can measure a significant correlation between brain anatomy and brain dynamics. This means that if we know how the brain is connected we can predict what the brain will do," Sporns said.
Sporns said the research team had further plants to look at more brains soon, to map brain connectivity as brains develop and age, and as they change in the course of disease and dysfunction.