For centuries, scientists have believed that a connection existed between the size of the brain and intellect.
New brain imaging methods (e.g., MRI, PET), now provide reliable assessments of in-vivo brain volume and allow accurate investigations of brain volume association with IQ.
In a new study, an international team of researchers, led by University of Vienna researchers Drs. Jakob Pietschnig, Michael Zeiler, and Martin Voracek, together with Lars Penke (University of Göttingen) and Jelte Wicherts (Tilburg University), performed a meta-analysis on the topic.
Their examinations of correlations between in-vivo brain volume and IQ has been published in the journal Neuroscience and Biobehavioral Reviews.
Based on the data from 148 samples comprising over 8000 participants, they report a robust but weak association between brain size and IQ. This association appeared to be independent of participant sex and age.
“The presently observed association means that brain volume plays only a minor role in explaining IQ test performance in humans. Although a certain association is observable, brain volume appears to be of only little practical relevance.
“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 Pietschnig.
The importance of brain structure compared to brain volume becomes evident when comparing different species. When considering absolute brain size, the sperm whale weighs in with the largest central nervous system. When controlling for body mass, the shrew is on the top of the list.
It appears that the way the brain is organized, and works, is more important than size.
For example, when considering other aspects of species anatomy, Homo sapiens never appear at the top at the list, as would be expected. Rather, differences in brain structure appear to be mainly responsible for between-species differences in cognitive performance.
Within humans, there are indications that a relationship between IQ and brain volume is questionable. For instance, differences in brain size between men and women are well-established, yielding larger brains of men compared to women. However, there are no differences in global IQ test performance between men and women.
Another example are individuals with megalencephaly syndrome (enlarged brain volume) who typically show lower IQ test performance than the average population.
“Therefore, structural aspects appear to be more important for cognitive performance within humans as well,” Pietschnig said.
Source: University of Vienna/EurekAlert