Non-gray circles and their connections represent 80, 70 and 60 percent
(from top to bottom) of all outgoing traffic within the sampled section of
a cortical region. | Photo by Indiana University
(January 20, 2016) Just as most of the world’s air travel passes through a few major hubs, the majority of information in the brain flows through similarly well-traveled routes, Indiana University scientists have found.
A new study, reported today in the journal Neuroscience, shows that 70 percent of all information within cortical regions in the brain passes through only 20 percent of these regions’ neurons.
"The discovery of this small but information-rich subset of neurons within cortical regions suggests this sub-network might play a vital role in communication, learning and memory," said Sunny Nigam, a Ph.D. candidate in the IU Bloomington College of Arts and Sciences' Department of Physics, who is the lead author on the study.
The scientists also report these high-traffic "hub neurons" could play a role in understanding brain health since this sort of highly efficient network -- in which a small number of neurons are more essential to brain function -- is also more vulnerable to disruption. That's because relatively small breakages can cause the whole system to "go down."
"The brain seems to favor efficiency over vulnerability," said John M. Beggs, associate professor of biophysics in the IU Bloomington Department of Physics, who is senior author on the paper. "In addition to helping us understand how the cortex processes information, this work could shed light on how the brain responds to neurodegenerative diseases that affect the 'network.'"
If the higher metabolic rates of hub neurons make them more vulnerable, for example, the resulting damage could be particularly harmful in conditions in which neurons are known to die, such as Alzheimer's disease.
The existence of neurons that carry the majority of information between cortical regions in the brain has been previously reported by Olaf Sporns, Distinguished Professor and Robert H. Shaffer Chair in the IU Bloomington Department of Psychological and Brain Sciences, who is a co-author on the paper. But the new study is the first to show that a similar dynamic exists in communication within cortical regions, or the "micro-structures," of the brain.
It is also the first to measure activity across a particularly large number of neurons in these regions.