Bigger Brains Expand Thinking Regions, But At A Cost

VIDEO: Big Brain Perks & Costs Dr. Armin Raznahan, NIMH Developmental Neurogenomics Unit 

A new study has discovered that the bigger the brain, the more its additional area is accounted for by growth in thinking areas of the cortex or outer mantle, at the expense of relatively slower growth in lower order emotional, sensory, and motor areas.

This mirrors the pattern of brain changes seen in evolution and individual development, with higher-order areas showing greatest expansion, say researchers at the National Institute of Mental Health (NIMH).

Researchers also found evidence linking the high-expanding regions to higher connectivity between neurons and higher energy consumption.

“Just as different parts are required to scale-up a garden shed to the size of a mansion, it seems that big primate brains have to be built to different proportions,” explained Armin Raznahan, M.D., Ph.D., of the NIMH Intramural Research Program (IRP).

“An extra investment has to be made in the part that integrates information, but that’s not to say that it’s better to have a bigger brain. Our findings speak more to the different organizational needs of larger vs. smaller brains.”

For the study, NIMH researchers, along with colleagues at more than six collaborating research centers, analyzed magnetic resonance imaging brain scans of more than 3,000 people from the Philadelphia Neurodevelopmental Cohort and the Human Connectome Project.

Cortex areas showing relatively more expansion in larger brains sit at the top of a network hierarchy and are specialized functionally, microstructurally and molecularly at integrating information from lower order systems, according to researchers.

Since this theme holds up across evolution, development and inter-individual variation, it appears to be a deeply ingrained biological signature, Raznahan suggested.

“Not all cortex regions are created equal. The high-expanding regions seem to exact a higher biological cost,” he said. “There’s biological ‘money’ being spent to grow that extra tissue. These regions seem to be greedier in consuming energy. They use relatively more oxygenated blood than low-expanding regions. Gene expression related to energy metabolism is also higher in these regions.

“It’s expensive, and nature is unlikely to spend unless it’s getting a return on its investment.”

Since people with certain mental disorders show alterations in brain size related to genetic influences, the new cortex maps may improve understanding of altered brain organization in disorders, the researchers note.

The higher expanding regions are also implicated across diverse neurodevelopmental disorders, so the new insights may hold clues to understanding how genetic and environmental changes can impact higher mental functions, researchers add.

“Our study shows there are consistent organizational changes between large brains and small brains,” said Raznahan. “Observing that the brain needs to consistently configure itself differently as a function of its size is important for understanding how the brain functions in health and disease states.”

The study was published in Science.

Source: National Institute of Mental Health

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