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Do you know which organ in the human body is the most energy-consuming? The brain consumes the most energy (when a person is at rest) – for work it needs up to 25% of all energy received as a result of metabolism. And only in humans the brain is so energy-consuming, which is not surprising. However, in other vertebrates, it still consumes quite a bit of energy – from 2 to 8%. As you might guess, energy consumption depends on the size of this organ and how developed it is. At the same time, it was previously believed that the brain of birds in terms of energy consumption does not differ from the brain of other animals, of course, taking into account the size. However, a recent study showed that this is not the case. Birds have a more advanced brain, and this applies not only to its energy efficiency.
Are birds smarter than mammals?
Birds have a smaller brain relative to their body size than mammals. However, some birds in their mental abilities surpass many mammals. For example, crows, whose brain weighs only 10-20 grams, are not inferior in this regard to chimpanzees, whose brain weight is 400 grams. The same applies to parrots, which sometimes simply amaze with their mental abilities. That is, there is no doubt that the brain of birds is more efficient.
In 2016, scientists managed to find out what this is connected with. As it turns out, avian brain neurons are much smaller than mammalian neurons. However, the density of nerve cells is 2-3 times higher. That is, to put it simply, the brain of birds is more densely “packed”. But how do birds manage to supply energy to such a large number of nerve cells?
How much more energy efficient are the bird brains?
Scientists from the Ruhr University managed to answer the question posed, as they reported in Current Biology. The authors of the work studied the brain of pigeons using positron emission tomography (PET). To estimate how much energy nerve cells consume, they injected modified glucose with a radioactive isotope of fluorine. The latter served as a contrast agent.
The emission of isotopes allowed scientists to estimate how quickly the brain absorbs glucose and how much energy it expends. Moreover, “fuel consumption” was measured both in ordinary, that is, awake pigeons, and after exposure to anesthesia, when the birds were in a state of complete rest.
To the surprise of the authors, it turned out that avian nerve cells consume three times less energy in any state than mammalian nerve cells. Scientists were not surprised by the fact that the nerve cells of birds consume less glucose. This was understandable, given that they are smaller in size. However, the authors did not expect the difference to be so large.
Why do bird brains use less energy?
Do not think that pigeons are stupid birds, and therefore their brain simply does not require a large amount of energy. Many studies suggest that the mental abilities of pigeons are greatly underestimated. Therefore, most likely, they have additional mechanisms that reduce the consumption of glucose by neurons.
It is possible that higher body temperature plays a role in this. But, most likely, there are other factors that are currently completely unknown to science. By the way, the temperature of the human brain is also not 36.6 degrees, as many might think, but much higher – it reaches 40 degrees in a healthy person.
Perhaps the brain of birds takes energy not only from glucose, but also from other molecules. However, the likelihood that other molecules can reduce the need for glucose by a factor of three is extremely small. Therefore, the authors of the work suggest that the neurons themselves in the brain of birds are able to work more economically.
The study showed that the development of the avian brain followed a different path from the evolution of the mammalian brain. According to scientists, humans were able to develop into Homo Sapiens only for the reason that in the course of evolution mechanisms arose that could supply a complex brain with a large amount of energy.
In birds, unlike mammals, along with the brain, its energy efficiency improved. If we draw an analogy with computers, then mammals increased the frequency of the processor and increased the power supply, and the birds took the path of reducing the internal architecture (technical process).