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Brain size less important than previously thought: Australian scientists

Efficiency of brain blood flow might be more cognitively crucial

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Researchers are deciphering the relationship between brain size and intelligence. (Unsplash photo)

Researchers are deciphering the relationship between brain size and intelligence. (Unsplash photo)

TAIPEI (Taiwan News) — A group of researchers may have discovered a new way to measure intelligence and found that the rate of blood flow to the brain might indicate why we are smarter than other primates rather than comparing the size of skulls.

It is reasonable to assume that increased intelligence corresponds with larger brain size: the number of nerve cells and metabolic rate increase almost proportionally as the brain becomes larger, said Roger Seymour, professor emeritus of physiology at the University of Adelaide.

According to him, the brain is like an energy-expensive computer in which more than 80 billion neurons and up to 1,000 trillion synapses (connections between neurons) comprise information processing. Synapses use up to 70 percent of the massive amount of energy the brain consumes, and the blood that carries oxygen to the brain is central to how synapses function.

Based on this fact, the researchers used ultrasound and magnetic resonance imaging to determine the size of the internal carotid arteries, which send blood to the cerebrum through the base of the skull. The more blood there is flowing into the brain, the more synaptic activity there is, which allows for more complicated brainwork.

By comparing the sizes of the internal carotid arteries of various hominins and other primates, the researchers debunked some previous assumptions. The early hominid genus Australopithecus, which included the well-known specimen "Lucy," actually had only two-thirds the blood flow of a chimpanzee or orangutan and half that of a gorilla, despite the latter's large brain volume.

The view that Lucy must have been smarter than these primates due to brain size is questionable.

Brain size less important than previously thought: Australian scientists

The human brain required more and more energy as it evolved. (The Conversation photo from Dr. Seymour)

Other research, however, indicates that intelligence is determined not just by the amount of fuel the brain can receive but also by how efficiently it works. Larger brains not only have more neurons but also fewer connections between these neurons, which translates into "lean, yet efficient neuronal connections," according to one of the study's researchers.

This explains why people with larger brains might be better at distinguishing crucial information from fluff and can use relatively low amounts of energy to maximize the speed at which they process information.

According to these findings, a bigger brain might have made us smarter, but not as much as efficient brain plumbing did.