Research helps unravel metabolism and human brain evolution

Contrary to what was assumed, the energy consumed by the brain is proportional to the number of neurons that the agency has

Foto: Divulgação/FAPAERJ
For the neuroscientist Suzana Herculano-Houzel, high cost
For the neuroscientist Suzana Herculano-Houzel, high cost

Study conducted at the Laboratory of Comparative Neuroanatomy of the Institute of Biomedical Sciences, Federal University of Rio de Janeiro (UFRJ), revealed that, contrary to what was assumed, the energy cost of the brain - the energy consumed so that it performs its activities - is proportional to the number of neurons you have.

According to neuroscientist Suzana Herculano-Houzel Scientist of Our State, FAPERJ, "Before this study, it was believed that the intensity of brain metabolism varied with the amount of body mass and not according to the number neurons. But it is precisely the opposite, "explains the professor, who is also the author of several books, including pills for Neuroscience for a Better Life (ed. Sextant) and why yawning is contagious? (Ed. Zahar). "The greater the absolute number of neurons in the brain, the greater the energy cost of brain functioning. The size of the brain simply does not influence the metabolism," she explains.

To study the change in brain metabolism between mammals, the neuroscientist compared the levels of glucose and oxygen consumed by the brain of six species of rodents and primates, including humans, with the number of neurons in their brains. The objective was to test the veracity of the ancient belief that bigger brains - like the man, who has three times the size of the primate brain - are larger neurons, which theoretically would need more energy, thereby increasing the metabolism per cell. Contradicting this hypothesis, the study showed that the energy cost per neuron is similar among different species. "The cerebral metabolic rate is similar among different species, even with different sizes of the brain. The high number of neurons is the factor that explains the high metabolic cost of human brain," he says.

In humans, the brain is ranked third in the ranking of agencies that require higher energy consumption of the body shortly after the skeletal muscles and liver. "The human brain seems to work very close to its maximum metabolic all the time," says neuroscientist. Simply put, while the cerebral metabolism of other mammals requires an energetic cost that varies only between 2% to 10% of the total energy of the body, in humans, the brain's energy cost is much higher: up to 20% of the cost energy throughout the body, although the court represent only 2% of body mass. The survey yielded the publication of articles in prestigious scientific journal Swiss Brain, Behavior and Evolution and the American PLoS One

effects of metabolism in human brain evolution

According to Professor Suzana Herculano-Houzel, this high energy cost of our brain suggests an important point of divergence of man in relation to other primates, which took place during the evolution of species. "Humans have invested in a large number of neurons, unlike the great apes. We have three times more neurons than gorillas and orangutans. But without the considerable increase in body mass that primates had," he says. "This suggests that it was an evolution strategy. There seems to be possible to have both the body and the number of giant neurons," he adds.

The teacher explains that the human brain is not the greatest (elephants and whales have brains much larger). However, the man is possibly what has the greatest number of neurons concentrated in one individual: 86 billion. "According to estimates from our laboratory, our ancestors, the australopithecines probably had as many neurons as the gorillas have today, about 30 billion, and by all indications, skills like that," he informs. So, to get recognized human skills today may have only been possible thanks to the huge increase in the number of neurons in the brain. "We believe that the first Homo, H. erectus, had almost twice as many neurons in our grandfather Australopithecines and we, Homo sapiens, arrived today to three times more neurons than the grandfather."

The explanation for the enormous number of neurons in the human brain has now may be the discovery by our ancestors, and techniques that enabled them to better nutrition. After all, it takes energy to keep this large number of neurons serving and consumption of raw foods does not offer the same potential energy to the body. "Getting enough energy to feed that brain of today might become possible thanks to the mastery of fire to prepare food, including meat. With the new eating habits acquired by Homo erectus, our ancestor, the brain has increased greatly in size during its existence and still more time left to use neurons for things other than hunting, "he concludes.

The study on the cellular composition of the brain of great apes was carried out in collaboration with Professor Jon Kaas of Vanderbilt University. Both the developments of the research is the study of cerebral metabolism or the study of the evolution of the organ were made possible by financial support from FAPERJ the researcher, the National Council for Scientific and Technological Development (CNPq) and the James McDonnell Foundation.


Source: FAPERJ