15 Oct 2015

Size doesn't matter! Having a big brain does not make you more intelligent

The question of whether a large brain equates to a high IQ has puzzled scientists for centuries.

Now researchers have found brain size only plays a small role in explaining why some humans are cleverer than others.

Instead, they believe how our brains are structured may hold the key to explaining IQ scores.

Since then, experts have been divided about whether he was right, with brain imaging methods such as MRI scans enabling them to make more reliable assessments of brain volume than ever before.

An international team of researchers led by the University of Vienna, examined the links between brain volume and IQ by studying data from 148 samples comprising 8,000 participants.

They found a robust but weak association between brain size and IQ, regardless of a participant’s sex and age, according to the study, published in the journal Neuroscience and Biobehavioral Reviews.
‘The presently observed association means that brain volume plays only a minor role in explaining IQ test performance in humans,’ Jakob Pietschnig from the Institute of Applied Psychology of the University of Vienna explained.

‘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.’
The importance of brain structure compared to brain volume becomes evident when comparing different species.

For example, the sperm whale has the largest central nervous system including its brain and when controlling for body mass, the shrew tops the list, with humans trailing far behind.

This suggests differences in brain structure appear to be mainly responsible for between-species differences in intelligence, the researchers said.

Building on the idea that brain size doesn’t directly correlate to IQ, it’s known that men have larger brains than women, but that there are no differences in global IQ test performance between the sexes.

People with megalencephaly syndrome - a growth development disorder in which the brain is abnormally large – typically score lower in IQ tests than the average person.

‘Therefore, structural aspects appear to be more important for cognitive performance within humans as well,’ Dr Pietschnig said.


Credit: Sarah Griffiths

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