text: Positive associations between human intelligence and brain size have been suspected for more than 150 years. Nowadays, modern non-invasive measures of in vivo brain volume (Magnetic Resonance Imaging) make it possible to reliably assess associations with IQ. By means of a systematic review of published studies and unpublished results obtained by personal communications with researchers, we identified 88 studies examining effect sizes of 148 healthy and clinical mixed-sex samples (>8000 individuals). Our results showed significant positive associations of brain volume and IQ (r=.24, R(2)=.06) that generalize over age (children vs. adults), IQ domain (full-scale, performance, and verbal IQ), and sex. Application of a number of methods for detection of publication bias indicates that strong and positive correlation coefficients have been reported frequently in the literature whilst small and non-significant associations appear to have been often omitted from reports. We show that the strength of the positive association of brain volume and IQ has been overestimated in the literature, but remains robust even when accounting for different types of dissemination bias, although reported effects have been declining over time. While it is tempting to interpret this association in the context of human cognitive evolution and species differences in brain size and cognitive ability, we show that it is not warranted to interpret brain size as an isomorphic proxy of human intelligence differences. 
   
   Copyright © 2015 Elsevier Ltd. All rights reserved. ||||| For centuries, scientists have been investigating the link between human brain size and intelligence, with several studies suggesting inconclusively that the bigger the brain, the smarter a person. 
   
   But a review of 88 studies involving more than 8,000 participants has now shown that even though a small link between brain volume and IQ exists, there's no evidence to suggest it's a causal one. Instead, it's the structure of your brain that seems play a larger role in determining how smart you are. 
   
   Although they're not perfect, IQ - or intelligence quotient - tests, are currently the best way we can measure someone's ability to rationally understand the world around them, as well as their memory, reasoning, and logic skills. And as a result, they're often used to help scientists try to make sense of what makes people more or less 'intelligent' than their peers. 
   
   In this instance, researchers from Austria, the Netherlands, and Germany compared IQ test results to participants' brain volumes, measured using brain imaging methods over multiple studies. 
   
   "Although a certain association is observable, brain volume appears to be of only little practical relevance," said lead researcher Jakob Pietschnig, from the University of Vienna in Austria. "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." 
   
   This isn't the first nail in the coffin for the 'bigger brain = better' argument. The first stumbling block was when scientists realised that humans - arguably the most intelligent animals on the planet - don't actually have the biggest brains in the animal kingdom relative to body size (that honour goes to the humble shrew). 
   
   To make up for that, scientists came up with a new way to measure brain size, known as the 'encephalisation quotient', which explains an animal's brain size relative to the expected brain size in related taxa. And when taking that into account, humans - thankfully - come at the top of the heap. 
   
   But in the new review, the researchers looked at both unpublished and published studies, and found that the link between brain volume and higher IQ had been overestimated and exaggerated in the literature. 
   
   This is because of publication bias, which means that journals are more willing to publish papers that find a strong link between something rather than those that find a small one, or are inconclusive. 
   
   But regardless, Pietschnig and his team showed that there was still a weak association between bigger brains and higher IQs throughout the research, which was independent of sex and age - but they also showed that brain size didn't have much predictive value when it came to measuring intelligence. 
   
   Their conclusion is supported by the fact that men consistently have higher brain volumes than women, but that there's no significant difference between the sexes when it comes to IQ tests. 
   
   "While it is tempting to interpret this association in the context of human cognitive evolution and species differences in brain size and cognitive ability, we show that it is not warranted to interpret brain size as an isomorphic proxy of human intelligence differences," the researchers conclude in Neuroscience and Behavioural Reviews. 
   
   And in case you were wondering, scientists have also studied Einstein's brain in great detail, and found that it's not that different from the rest of ours. 
   
   So next time you feel sad about the size of your head, just remember that you have as much potential in there as even the largest brains out there. ||||| The brain structure is more important than the size 
   
   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 from the Universities of Vienna (Austria), Göttingen (Germany), and Tilburg (Netherlands) 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. 
   
   
   
   As early as 1836, the German physiologist and anatomist Friedrich Tiedemann, in an article in the Philosophical Transactions, expressed his opinion that "there is undoubtedly a connection between the absolute size of the brain and the intellectual powers and functions of the mind". With the advent of brain imaging methods (e.g., MRI, PET), reliable assessments of in-vivo brain volume and investigations of its association with IQ are now possible. 
   
   
   
   Now, an international team of researchers, led by University of Vienna researchers Jakob Pietschnig, Michael Zeiler, and Martin Voracek from the Faculty of Psychology, together with Lars Penke (University of Göttingen) and Jelte Wicherts (Tilburg University), published a meta-analysis examining correlations between in-vivo brain volume and IQ in 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", explains Jakob Pietschnig from the Institute of Applied Psychology of the University of Vienna. 
   
   
   
   Brain structure vs. brain size 
   
   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. 
   
   
   
   Publication in "Neuroscience and Biobehavioral Reviews": 
   
   Pietschnig, J., Penke, L., Wicherts, J. M., Zeiler, M., & Voracek, M. (2015). Meta-analysis of associations between human brain volume and intelligence differences: How strong are they and what do they mean? Neuroscience and Biobehavioral Reviews, in press. 
   
   DOI: http://dx.doi.org/doi:10.1016/j.neubiorev.2015.09.017 
   
   
   
   http://www.sciencedirect.com/science/journal/aip/01497634
target: – If brain size relative to body size determines IQ, the venerable shrew would be the smartest creature on the planet. But it doesn't, and it's not, and scientists from Austria, the Netherlands, and Germany have combed through 88 studies with more than 8,000 participants to confirm in the journal Neuroscience and Behavioral Reviews that when it comes to intelligence, brain size simply doesn't matter. "Although a certain association is observable, brain volume appears to be of only little practical relevance," says Jakob Pietschnig from the Institute of Applied Psychology at the University of Vienna. The researchers write that "positive associations between human intelligence and brain size have been suspected for more than 150 years." Why the long-held belief in such a link despite a lack of concrete evidence for it? It may partly be the result of publication bias, reports ScienceAlert. This means that journals more readily publish findings with strong links between subjects than weak or inconclusive links. And that's all that Pietschnig and his team found when they reviewed published and unpublished studies—a link too small to have any discernible effect. "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," Pietschnig adds. This helps explain why men, who tend to have larger brains than women, do not perform better on IQ tests. To be small-minded, then, should be construed in only a metaphorical sense. (Check out what has been hiding in brains for centuries until this year.)