A century-old paradigm has been upended — brain shape matters more than neural connectivity

The shape of our brain rather than the interactions between different regions plays a pivotal role in influencing our thoughts, emotions and actions.

For more than a hundred years, scientists have believed that our thoughts, feelings, and dreams are shaped by the way different brain regions interact across a vast network of trillions of cellular connections.

However, a recent study led by the team at Monash University’s Turner Institute of Brain and Mental Health examined more than 10,000 distinct maps of human brain activity and discovered that the general shape of an individual’s brain has more influence on cognitive processes, emotions and behavior than the complex neural connectivity.

The study, which was recently published in the prestigious journal, nature He brings together approaches from physics, neuroscience, and psychology to overturn the century-old paradigm that stresses the importance of complex brain connectivity, and instead identifies the previously underappreciated relationship between brain shape and activity.

Lead author and research fellow Dr James Bang, from the Turner Institute and Monash University’s School of Psychological Sciences, said the findings were important because they greatly simplified the way we can study how the brain works, develops and ages.

Alex Fornetto (left) and James Pang studied more than 10,000 MRI images to determine the important brain shape. Credit: Monash University

“The work opens up opportunities to understand the effects of diseases such as dementia and stroke by looking at models of brain shape, which are much easier to work with than models of the whole set of connections in the brain,” said Dr. Pang.

“We have long thought that certain thoughts or sensations trigger activity in specific parts of the brain, but this study reveals that organized patterns of activity are stimulated across nearly the entire brain, much like the way a musical note arises from vibrations that occur along the entire length of a violin string, rather than just an isolated part,” he said.

The research team used magnetic resonance imaging (MRI) to study eigenmodes, which are the natural patterns of vibration or excitation in a system, in which different parts of the system are excited at the same frequency. Automodules are typically used to study physical systems in fields such as physics and engineering, and have only recently been adapted to study the brain.

This work focused on developing the best way to efficiently construct eigenmodes for the brain.

Co-lead author Dr Kevin Aquino, from BrainKey and the University of Sydney, said: “Just as the resonant frequencies of violin strings are determined by their length, density and tension, brain eigenmodes are determined by their structural properties – physical, geometric and anatomical -, but the most important specific properties have remained a mystery.”

The team, led by Turner Institute and ARC School of Psychological Science Fellow Professor Alex Fornetto, compared how subjective profiles obtained from brain-shape models can explain different patterns of activity when compared with subjective profiles obtained from brain-connectivity models.

“We found that eigenmodes defined by brain geometry – their contours and curvature – represent the strongest anatomical constraint on brain function, just as the shape of a cylinder affects the sounds it can make,” said Professor Fornetto.

“Using mathematical models, we confirmed theoretical predictions that the close connection between geometry and function is driven by wave-like activity propagating throughout the brain, just as the shape of a pond affects the ripples of waves formed by a falling pebble,” he said.

“These findings raise the possibility of predicting brain function directly from its shape, opening up new avenues for exploring how the brain contributes to individual differences in behavior and risk for psychiatric and neurological diseases.”

The research team found that across more than 10,000 MRI activity maps, obtained as subjects performed various tasks developed by neuroscientists to explore the human brain, the activity was dominated by subjective patterns with spatial patterns that had very long wavelengths, extending over distances greater than 40 millimeters.

“This finding runs counter to conventional wisdom, in which activity during various tasks is often assumed to occur in focal and isolated regions of elevated activity, and tells us that traditional methods of brain mapping may only show the tip of the iceberg when it comes to understanding how the brain works,” said Dr. Pang.

Reference: “Engineering Limitations on Human Brain Functions” By James C. Pang, Kevin M. Aquino, Marian Oldenkel, Peter A. Robinson, Ben de Fulcher, Michael Breakspeare, Alex Fornetto, May 31, 2023, Available Here. nature.
DOI: 10.1038/s41586-023-06098-1