The strong belief in the connection between a large brain and high intelligence has been passed down from generation to generation. This notion dates back to 1836 when Friedrich Tiedemann, a German physiologist and anatomist, wrote, "there is undoubtedly a connection between the absolute size of the brain and the intellectual powers and functions of the mind."
Discrediting the notion that a bigger brain size relates to higher levels of IQ, researchers found there is a very weak link that connects the two. An international team of researchers analyzed data from 8,000 participants. Using brain imaging procedures such as magnetic resonance imaging and positron emission tomography scans, the scientists were able to examine the in vivo brain volume of 148 samples. Proving correlation between brain size and IQ was made possible through a meta-analysis.
Men have naturally larger brains compared to women but this made no difference in the two groups' global IQ test performance. The researchers pointed out that brain structure and integrity are better biological foundations of IQ levels.
If one is looking at brain volume or size alone across species, the sperm whale beats the entire mammal species in having an absolute brain size and the biggest central nervous system. Researchers expressed that brain structure is responsible in differentiating cognitive performance across species.
Humans with bigger brains do not always have high levels of IQ. Take for instance patients with megalencephaly syndrome, a condition characterized by an abnormally large brain. Typical results show lower IQ levels compared to the average person. This supports the paper's claim that brain structure is responsible for cognitive performance, and not brain volume.
"Brain volume plays only a minor role in explaining IQ test performance in humans. Rather, brain structure and integrity appear to be more important as a biological foundation of IQ, whilst brain size works as one of many compensatory mechanisms of cognitive functions," said researcher Jakob Pietschnig from the University of Vienna's Institute of Applied Psychology.
The paper is a joint collaboration between the University of Vienna, University of Göttingen and the Tilburg University. The researchers published their study in the Neuroscience & Biobehavioral Reviews journal on Oct. 9.
