Brain scans (stock image). Credit: © nimon_t / Fotolia
Is brain size related to cognitive ability of humans? This question has captured the attention of scientists for more than a century. An international team of researchers provides no evidence for a causal role of brain size for IQ test performance. In a meta-analysis of data from more than 8000 participants, they show that associations between in vivo brain volume and IQ are small. 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,” explains Jakob Pietschnig from the Institute of Applied Psychology of the University of Vienna.
The importance of brain structure compared to brain volume becomes already 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. Similar results emerge when considering other aspects of species anatomy: Homo sapiens never appears 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 Homo sapiens, there are indications that render a large association between IQ and brain volume similarly 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,” concludes Jakob Pietschnig. http://medienportal.univie.ac.at/presse/aktuelle-pressemeldungen/detailansicht/artikel/larger-brains-do-not-lead-to-high-iqs/
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