Consistent Networks

A new study has established that functional networks are highly consistent across the brains of many individuals.

Functional networks look delicious, don't they?

The research, published in the journal Cerebral Cortexcorrelated huge amounts of data on the connectivity of macaque visual cortices – particularly the layers known as V1, V3, and V4 – and confirmed that between one monkey’s brain and another, these functional networks follow extremely similar patterns.

The question of how consistent primate functional networks are has been a controversial issue for years. Most brains are reasonably similar to others from the same species on a structural level – but the complexity of their synaptic connections is mind blowing: a single macaque brain contains more than 100 billion neurons, which form more than 100 trillion synapses.

Thus, it’s only in the past few years that scientists have even been able to map the functional connectivity of a single brain – much less compare functional connections across a whole group of primates. It’s also led to a lot of debate about how similar such complex networks can possible be be to one another.

Well, the answer is (in technical terminology), “really really similar.”

The brain is characterized by a highly consistent, weighted network among the functional areas of the cortex, which are responsible for such functions as vision, hearing, touch, movement control and complex associations. The study revealed that such cortical networks and their properties are reproducible from individual to individual.

This network-comparison adventure began when a group of neuroanatomists in France, led by Henry Kennedy, contacted the University of Notre Dame’s Interdisciplinary Center for Network Science and Applications (iCeNSA). The French scientists commissioned the Center – known for its expertise at analyzing complex networks for fields as diverse as sociology and epidemiology – to check out the brain-to-brain consistency of a massive amount of macaque functional connectivity data they’d gathered. The iCeNSA assembled a team led by Dr. Maria Ercsey-Ravasz and Dr. Zoltan Toroczkai, two physicists who tore into the data like King Henry I at a lamprey-eating contest:

A top-down approach called functional decomposition, identifying bundles within the brain, helps overcome the sheer data volume. The macaque brain has 83 [major functional] areas; the human brain more than 120.

One of the reasons functional connectivity is so consistent from one brain to another, the teams found, is that neural connections seem to organize themselves based on a consistent set of principles across a variety of scales – in other words, they exhibit some fractal characteristics.

“It looks like there is some sort of general algorithm that is being run in this brain network,” [Toroczai] says. “The wiring is very strange.”

What these strange organizational principles are – and why primate brains have evolved to rely on them – are questions the teams plan to explore in the near future.

Even more exciting, they hope these new methods of data analysis may help them unravel one of neuroscience’s ultimate mysteries: how, exactly, brains encode information at all.

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