Our brain's high energy demands, particularly in certain key areas, may have enabled us to evolve uniquely advanced cognitive traits.
The human brain has greater energy demands than that of any other animal, especially in certain important regions, which may have been key to the evolution of our complex cognition. Knowing how energy use differs across the brain could also help us better understand and treat certain conditions, such as Alzheimer’s disease and depression.
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| Magnetic resonance imaging scans showing healthy human brains SIMON FRASER/SCIENCE PHOTO LIBRARY |
Some mammals have bigger brains and more nerve cells, or neurons, than humans, making it unclear how we evolved a uniquely advanced ability to think critically and use language to communicate.
Valentin Riedl at the Technical University of Munich in Germany and his colleagues wondered whether understanding how our brains use energy could help to explain our complex cognition.
They therefore imaged 30 people’s brains to measure how well electrical signals, generated by neurons, in different regions of the organ synchronised with signals across the rest of the brain. They also used a technique called positron emission tomography to detect how much sugar is used as an energy source by different brain regions.
“We already knew the overall energy that the brain consumes, but how the energy use is distributed across different brain regions was unknown,” says Riedl.
As expected, the researchers found that the brain regions with signalling patterns that were more synchronised with the rest of the brain generally used up more energy. However, regions in the fronto-parietal area of the brain’s outer layer – involved in reading, memory and problem-solving – used up 67 per cent more energy relative to their signalling synchronisations, on average, compared with other brain regions involved in movement and sensing the environment.
“Those regions that consume a lot of energy, relative to how connected they are, are located in regions that expanded the most in the evolution of humans,” says Riedl. “This suggests that these regions may have played an important role in the emergence of complex cognition.”
The team also found that these energy-costly brain regions are involved in modulating levels of chemicals, such as dopamine, serotonin and noradrenaline, that help to integrate information across broad areas of the brain.
“These chemicals are found in other animals, including other primates and mice, but it could be that humans have more of the energy-costly brain regions controlling them than other animals,” says Riedl.
With further research, the findings could help to drive our understanding of some brain-related conditions. “As we now know, there are certain regions that spend more energy for certain complex processes, maybe those are regions that are more easily prone to deficits in energy, which could lead to Alzheimer’s or depression,” says Riedl.
“This is a very interesting study that shows the brain has different energy demands in different regions and networks,” says David Geary at the University of Missouri. “The variation in energy costs is especially interesting, because these are pronounced in brain areas and systems that differ the most from other primates.”
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