Rich-Club Organization in Effective Connectivity among Cortical Neurons
Sunny Nigam et al. JNeurosci 2016
Just as most of the world’s air travel passes through a few major hubs, majority of the information in the brain flows via similarly well-travelled routes, scientists including one of Indian origin have found.
The study shows that 70 per cent of all information within cortical regions in the brain passes through only 20 per cent 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 lead author Sunny Nigam, a PhD candidate at the Indiana University in US.
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.
“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’,” said senior author John M Beggs, associate professor at the Indiana University.
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 reported earlier.
However, 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.
Scientists recorded small electrical impulses from up to 500 neurons from the somatosensory cortex – the part of the brain responsible for the sense of touch — measuring a large volume of traffic across a relatively small area.
They were able to show the flow of both outgoing and incoming information within the living neural network by combining data from very high-resolution imaging technology with complex biophysical computer simulations of the brain.
“This is the first study to combine such a large number of neurons with such high temporal resolution,” Nigam said.
“We can actually detect the direction of the communication flowing between neurons, creating a ‘transportation map’ from the connections within the cortex,” he said.
The experiments, conducted in live and tissue samples, were based in rodents. However, similar high-traffic zones in the cortex have been shown to exist in more advanced mammals, including primates and adult humans.
The study was published in the journal Neuroscience. — PTI