The Relationship of Our Brain Size and Fold Number to IQ

The brain consists of two lobes and two layers. Gray matter consists of small blood vessels, and somas in the outer layer; In the inner layer, there is white matter consisting of myelinated axons [1].

Figure 1: The outer layer of the brain and the inner layer of the brain.

As humans evolved, our brains grew to perform higher functions that set them apart from other animals. This enlarged brain had to become tight and dense to fit into his skull. [3]

Gyrification is the process of forming the characteristic folds of the gray cerebral cortex. With the development of the fetus, which has a very smooth and small brain, the neurons grow, migrate to different parts of the brain and have projections and recesses called the gyrus and sulcus. The reason for these indentations and protrusions is to increase the surface area and to be able to fit in the skull proportionally to our body size while preserving the connective structure of the brain. When we opened these folds, it would be the length of a pillowcase [2,3, 4].

Figure 2: Process of gyrification

There is no linear relationship between brain size, curve and intelligence. For example, dolphin brains are roughly the same size as human brains, but they do not indicate that they are any more intelligent. If we were to make a comparison among people, just because a person with Achondroplasia has a smaller brain does not mean they are more intelligent than a gigantism person [4, 5].

It is not the size of the brain that makes a living thing more intelligent, but the ratio of the mass of the brain to the total mass of the living thing. While this ratio is one in fifty in a human weighing approximately seventy kilograms, the ratio of brain mass to the total mass of the animal is approximately one hundred and twenty in birds. As can be seen, it is seen that the person with a high rate is more intelligent in high-level functions such as memory and communication [5].

Research conducted by researcher Gideon Nave and researcher Philipp Koellinger on the relationship between a larger brain and test performance revealed some differences between male and female brains. As with the same size, there are differences between their volumes. It was also observed that the cerebral cortex tended to be thicker in women. This showed that they have smaller brains than men. This may explain the fact that there is no difference in cognitive performance despite the size difference [6].

Figure 3: The “connectome maps” reveal the differences between the male brain (seen in blue) and the female brain (orange)

They found that people with higher IQs had stronger connectivity between specific brain regions, not brain size or the number of folds. He noted that clusters of mesh nodes in the frontal and parietal cortex and the cortical and subcortical areas are more strongly interconnected and more intensely active. It also shows that brain regions are segregated so that they are ready to discard irrelevant and distracting information using less communication with other brain regions. It also has a low degree of neurite density and orientation distribution [7].

A collaboration of key neuroscientists at the Free University Amsterdam with neurosurgeons and clinical psychologists at the University of Amsterdam Medical Center found that using human subjects, cells from people with higher IQs have longer and more complex dendrites and faster action potentials, resulting in faster action potentials. They found it to have a fast response time [8].

Figure 4: Differences between low-IQ individuals and high-IQ individuals

When we learn something, we develop new connections, not new wrinkles. It is not just in the form of additional sulci and gyrus. This phenomenon is called brain plasticity. Brain plasticity refers to the structural and functional changes that the brain tissue undergoes under external factors. It is a mechanism used in physiological processes such as learning and memory and the repair of damaged tissue. The researchers discovered that as animals like mice learn, the blood cells that support synapses and neurons grow and increase in number [9].

Learning new things causes you to make new connections in the brain. For example, playing chess, playing a new sport, learning a new language, reading a book, solving puzzles, and meditating are activities that increase the level of IQ [10].

Conclusion

To summarize, the size of the brain and the number of folds are not related to IQ; It has been observed that it is related to the development of connections between folds. For these connections to increase, active learning must take place. It also showed the fact that although women have smaller brains, there is no difference in cognitive performance between them and men. In short, it was observed that there was no gender-related IQ difference. Individuals with lower IQs have a greater distribution of neurite density and orientation [7].

References:

  1. https://theconversation.com/brain-wrinkles-and-folds-matter-researchers-are-studying-the-mechanics-of-how-they-form-170194
  2. https://science.howstuffworks.com/life/inside-the-mind/human-brain/10-brain-myths.htm#page=5
  3. https://evrimagaci.org/yeni-bir-sey-ogrendigimizde-yeni-beyin-kivrimlari-edinir-miyiz-7741
  4. https://science.howstuffworks.com/life/inside-the-mind/human-brain/10-brain-myths.htm#page=5
  5. https://www.newworldai.com/relationship-between-the-size-of-the-brain-and-intelligence/#:~:text=The%20wrong%20idea%20is%20that,your%20brain%20is%20less%20intelligent.
  6. https://penntoday.upenn.edu/news/bigger-brains-are-smarter-not-much
  7. https://www.medicalnewstoday.com/articles/320152#Where-does-causality-lie?
  8. https://www.humanbrainproject.eu/en/follow-hbp/news/brains-of-smarter-people-have-bigger-and-faster-neurons/
  9. https://science.howstuffworks.com/life/inside-the-mind/human-brain/10-brain-myths.htm#page=5
  10. https://www.gercekbilim.com/iqyu-arttirmanin-10-bilimsel-yolunu-biliyor-musunuz/

Figure References:

  1. https://images.theconversation.com/files/437321/original/file-20211213-17-900awf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip
  2. https://www.liebertpub.com/doi/10.1089/bfm.2018.29079.mbb
  3. https://evrimagaci.org/sinirbilimin-kadin-ve-erkekleri-ayristirmakta-kullanilan-venus-ve-mars-klisesini-basindan-savma-vakti-geldi-1850
  4. https://www.researchgate.net/profile/Rex-Jung/publication/325155490/figure/fig1/AS:626597262540801@1526403837398/Schematic-depiction-of-differences-between-low-IQ-and-high-IQ-individuals-with-regard-to.png

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