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Intelligence and the Human Brain

Human brain and IQ word on black background. 3D illustrationWhat is human intelligence? How do you quantify it? These questions need to be addressed before discussing the connection between intelligence and the human brain.

So, first the definition. We all have our own ideas about what intelligence is. To keep things simple, we use the Encyclopaedia Britannica definition: “human intelligence is the mental quality that consists of the abilities to learn from experience, adapt to new situations, understand and handle abstract concepts, and use knowledge to manipulate one’s environment.”

Next, how do you quantify intelligence? Commonly, a combination of standardized tests is used to measure the abilities listed above and more. The results yield a number—the Intelligence Quotient (IQ). This number is what many people are familiar with as a measure of intelligence. However, IQ test results are somewhat influenced by social and cultural factors. Therefore, many researchers also use a measurement called the g-factor (general factor of intelligence). Measurements of additional abilities go into calculating the g-factor such as reasoning, memory, vocabulary, spatial ability, processing speed, and more. Studies have shown that the g-factor is strongly influenced by heredity (biological and genetic factors), but less affected by the environmental factors that influence IQ. Nevertheless, it has been shown that the IQ is a fair approximation of the g-factor, so brain research often involves either or both.

Now, how are intelligence and the human brain related? Using modern brain imaging techniques such as fMRI (Functional Magnetic Resonance Imaging) and PET (Positron Emission Tomography) scans to study brain activity, coupled with IQ and g-factor measurements, researchers are discovering brain characteristics that correlate with intelligence. These characteristics include the amount and distribution of grey matter and differences in neural networking. (1) As one study shows, in individuals with higher intelligence “the areas of the brain which are associated with learning and development show high levels of variability, meaning that they change their neural connections with other parts of the brain more frequently, over a matter of minutes or seconds.” The study goes on to say, “the more variable a brain is, and the more its different parts frequently connect with each other, the higher a person’s IQ and creativity are.” (2)

There are other interesting findings. For example, if one compares groups with different g-factors that solve the same problem, there is much higher brain activity in the people with the lower g-factors than those with higher g-factors. The interpretation is that the less intelligent people require much more brain activity to arrive at the solution. It also was found that when comparing a group of men with a group of women having the same IQ and g-factors, men showed completely different areas of brain activity than women when solving the same problem. This finding provides a clue on how to restore brain functions to people with brain injuries (i.e., by somehow redirecting brain activity through uninjured parts of the brain). (3)

Although the above examples of studies using brain scans are promising, many more years of brain research are expected to be required, first to obtain a much fuller understanding of how the different parts of the brain work together, and then to be able to use that information. If you are interested, Reference 3 provides a good, easy-to-read overview of advances in this field. And for more technical articles on brain networking and intelligence see References 4-7.

Why is all this important? Ultimately, a complete revolution in our way of life could be unleashed by the ability to manipulate brain functions—to repair brain injuries, cure/prevent mental illnesses, and even to make humans more intelligent. One more door, waiting to be opened, with an unknown future on the other side.


  1. Roberto Colom, Rex Jung, and Richard Haier, “Distributed brain sites for the g-factor of intelligence,” NeuroImage, 31 (2006) 1359-1365, https://static1.squarespace.com/static/538634aee4b0b15c0516a524/t/538774afe4b07a163543ab01/1401386159041/distributed-brain-sites-for-the-g-factor-of-intelligence.pdf
  2. University of Warwick, “Human intelligence measured in the brain,” com, July 18, 2016, https://www.sciencedaily.com/releases/2016/07/160718110938.htm
  3. Richard Haier and Rex Jung, “Brain Imaging Studies of Intelligence and Creativity: What is the Picture for Education?” Roeper Review, 30 (2008) 171-180, https://podcasts.shelbyed.k12.al.us/sspears/files/2015/01/Brain-Imaging-Studies-of-Intelligence-and-Creativity-What-is-the-picture-of-Education.pdf
  4. Michael Ferguson, Jeffrey Anderson, and R. Nathan Spreng, “Fluid and flexible minds: Intelligence reflects synchrony in the brain’s intrinsic network architecture,” Network Neuroscience, 1 (June 2017), no. 2,192-207, https://www.mitpressjournals.org/doi/full/10.1162/netn_a_00010
  5. Kirsten Hilger, Matthias Ekman, Christian Fiebach, and Ulrike Basten, “Intelligence is associated with the modular structure of intrinsic brain networks,” Scientific Reports, 7 (November 2017), Article no. 16088, https://www.nature.com/articles/s41598-017-15795-7
  6. Youngwoo Yoon et al, “Brain Structural Networks Associated with Intelligence and Visuomotor Ability,” Scientific Reports, 7 (2017), Article no. 2177, https://www.nature.com/articles/s41598-017-02304-z
  7. Aron Barbey, “Network Neuroscience Theory of Human Intelligence,” Trends in Cognitive Sciences, 22 (January 2018), no. 1, 8-20, https://www.sciencedirect.com/science/article/pii/S1364661317302218


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