Gender Differences

  • In general, males are better at spatial tasks involving mental rotation.
  • In general, females have superior verbal skills.
  • Males are far more likely to pursue math or science careers, but gender differences in math are not consistent across nations or ages.
  • A number of imaging studies have demonstrated that the brains of males and females show different patterns of activity on various tasks.
  • Nicotine has been shown to differentially alter men's and women's brain activity patterns so that the differences disappear.
  • Both estrogen and testosterone have been shown to affect cognitive function.
  • Training has been shown to bring parity to differences in cognitive performance between the sexes.
  • Age also alters the differences between men and women.

Widely cited gender differences in cognition

It is clear that there are differences between the genders in terms of cognitive function; it is much less clear that there are differences in terms of cognitive abilities. Let me explain what I mean by that.

It's commonly understood that males have superior spatial ability, while females have superior verbal ability. Males are better at math; females at reading. There is some truth in these generalizations, but it's certainly not as simple as it is portrayed.

First of all, as regards spatial cognition, while males typically outperform females on tasks dealing with mental rotation and spatial navigation, females tend to outperform males on tasks dealing with object location, relational object location memory, and spatial working memory.

While the two sexes score the same on broad measures of mathematical ability, girls tend to do better at arithmetic, while boys do better at spatial tests that involve mental rotation.

Having said that, it does depend where you're looking. The Programme for International Student Assessment (PISA) is an internationally standardised assessment that is given to 15-year-olds in schools. In 2003, 41 countries participated. Given the constancy of the gender difference in math performance observed in the U.S., it is interesting to note what happens in other countries. There was no significant difference between the sexes in Australia, Austria, Belgium, Japan, the Netherlands, Norway, Poland, Hong Kong, Indonesia, Latvia, Serbia, and Thailand. There was a clear male superiority for all 4 content areas in Canada, Denmark, Greece, Ireland, Korea, Luxembourg, New Zealand, Portugal, the Slovak Republic, Liechtenstein, Macao and Tunisia. In Austria, Belgium, the United States and Latvia, males outperformed females only on the space and shape scale; in Japan, the Netherlands and Norway only on the uncertainty scale. And in Iceland, females always consistently do better than males!

Noone knows why, but it is surely obvious that these differences must lie in cultural and educational factors.

Interestingly, the IEA Third International Mathematics and Science Study (TIMSS) shows this developing -- while significant gender differences in mathematics were found only in 3 of the 16 participating OECD countries for fourth-grade students, gender differences were found in 6 countries at the grade-eight level, and in 14 countries at the last year of upper secondary schooling.

This inconsistency is not, however, mirrored in verbal skills -- girls outperform boys in reading in all countries.

Gender differences in language have been consistently found, and hardly need reiteration. However, here's an interesting study: it found gender differences in the emerging connectivity of neural networks associated with skills needed for beginning reading in preschoolers. It seems that boys favor vocabulary sub-skills needed for comprehension while girls favor fluency and phonic sub-skills needed for the mechanics of reading.The study points to the different advantages each gender brings to learning to read.

There's a lesson there.

There are other less well-known differences between the sexes. Women tend to do better at recognizing faces. But a study has found that this superiority applies only to female faces. There was no difference between men and women in the recognition of male faces.

Moreover, pre-pubertal boys and girls have been found to be equally good at recognizing faces and identifying expressions. However, they do seem to do it in different ways. Boys showed significantly greater activity in the right hemisphere, while the girls' brains were more active in the left hemisphere. It is speculated that boys tend to process faces at a global level (right hemisphere), while girls process faces at a more local level (left hemisphere).

It's also long been recognized that women are better at remembering emotional memories. Interestingly, an imaging study has revealed that the sexes tend to encode emotional experiences in different parts of the brain. In women, it seems that evaluation of emotional experience and encoding of the memory is much more tightly integrated.

But of course, noone denies that there are differences between men and women. The big question (one of the big questions) is how much, if any, is innate.

Studies of differences, even at the neural level, don't demonstrate that. It's increasingly clear that environmental factors affect all manner of thing at the neural level. However, one study of 1-day-old infants did find that boys tended to gaze at three-dimensional mobiles longer than girls did, while girls looked at human faces longer than boys did.

Of course, even a 1-day-old infant isn't entirely free of environmental influence. In this case, the most important environmental influence is probably hormones.

Hormones and chemistry

A lot of studies in recent years have demonstrated that estrogen is an important player in women's cognition. Spatial ability in particular seems vulnerable to hormonal effects. Women do vary in their spatial abilities according to where they are in the menstrual cycle, and there is some evidence that spatial abilities (in both males and females) may be affected by how much testosterone is received in the womb.

Another study has found children exposed to higher levels of testosterone in the womb also develop language later and have smaller vocabularies at 2 years of age.

Hormones aren't the only chemical affecting male and female brains differently. Significant differences have been found in the brain activity of men and women when engaged in a broad range of activities and behaviors. These differences are more acute during impulsive or hostile acts. But — here's the truly fascinating thing — nicotine causes these brain activity differences to disappear. A study has found that among both smokers and non-smokers on nicotine, during aggressive moments, there are virtually no differences in brain activity between the sexes. A finding that supports other studies that indicate men's and women's brains respond differently to the same stimuli — for example, alcohol.

What does all this mean? Well, let's look at the question that's behind the whole issue: are men smarter than women? (or alternately, are women smarter than men?)

Is one sex smarter than the other?

Here's a few interesting studies that demonstrate some more differences between male and female brains.

A study of some 600 Dutch men and women aged 85 years found that the women tended to have better cognitive speed and a better memory than the men, despite the fact that significantly more of the women had limited formal education compared to the men. This may be due to better health. On the other hand, there do appear to be differences in the way male and female brains develop, and the way they decline.

For example, women have up to 15% more brain cell density in the frontal lobe, which controls so-called higher mental processes, such as judgement, personality, planning and working memory. However, as they get older, women appear to shed cells more rapidly from this area than men. By old age, the density is similar for both sexes.

A study of male and female students (aged 18-25) has found that men's brain cells can transmit nerve impulses 4% faster than women's, probably due to the faster increase of white matter in the male brain during adolescence.

An imaging study of 48 men and women between 18 and 84 years old found that, compared with women, men had more than six times the amount of intelligence-related gray matter. On the other hand, women had about nine times more white matter involved in intelligence than men did. Women also had a large proportion of their IQ-related brain matter (86% of white and 84% of gray) concentrated in the frontal lobes, while men had 90% of their IQ-related gray matter distributed equally between the frontal lobes and the parietal lobes, and 82% of their IQ-related white matter in the temporal lobes. Despite these differences, men and women performed equally on the IQ tests.

It has, of course, long been suggested that women are intellectually inferior because their brains are smaller. A study involving the intelligence testing of 100 neurologically normal, terminally ill volunteers found that a bigger brain size is indeed correlated with higher intelligence — but only in certain areas, and with odd differences between women and men. Verbal intelligence was clearly correlated with brain size for women and — get this — right-handed men! But not for left-handed men. Spatial intelligence was also correlated with brain size in women, but much less strongly, while it was not related at all to brain size in men.

Also, brain size decreased with age in men over the age span of 25 to 80 years, suggesting that the well-documented decline in visuospatial intelligence with age is related, at least in right-handed men, to the decrease in cerebral volume with age. However age hardly affected brain size in women.

What is all this telling us?

Male and female brains are different: they develop differently; they do things differently; they respond to different stimuli in different ways.

None of this speaks to how well information is processed.

None of these differences mean that individual brains, of either sex, can't be trained to perform well in specific areas.

Here’s an experiment and a case study which bear on this.

It's all about training

The experiment concerns rhesus monkeys. The superiority of males in spatial memory that we're familiar with among humans also occurs in this population. But here's the interesting thing — the gender gap only occurred between young adult males and young untrained females. In other words, there was no difference between older adults (because performance deteriorated with age more sharply for males), and did not occur between male and female younger adults if they were given simple training. Apparently the training had little effect on the males, but the females improved dramatically.

The “case study” concerns Susan Polgar, a chess master. You can read about her in a recent article ( ), which I noticed because the Polgar sisters are a well-known example of “hot-housing”. I cited them in my own article on the question of whether there is in fact such a thing as innate talent. Susan Polgar and her sisters are examples of how you can train “talent”; indeed, whether there is in fact such a thing as “talent” is a debatable question. Certainly you can argue for a predisposition towards certain activities, but after that … Well, even geniuses have to work at it, and while you may not be able to make a genius, you can certainly create experts.

This article was provoked, by the way, by comments by the President of Harvard University, Lawrence Summers, who recently stirred the pot by giving a speech arguing that boys outperform girls on high school science and math scores because of genetic differences between the genders, and that discrimination is no longer a career barrier for female academics. Apparently, during Dr Summers' presidency, the number of tenured jobs offered to women has fallen from 36% to 13%. Last year, only four of 32 tenured job openings were offered to women.

You can read a little more about what Dr Summers said at,7348,1393079,00.html, and there's a rather good response by Simon Baron-Cohen (professor in the departments of psychology and psychiatry, Cambridge University, and author of The Essential Difference) at:,9865,1399109,00.html


  • Canli, T., Desmond, J.E., Zhao, Z. & Gabrieli, J.D.E. 2002. Sex differences in the neural basis of emotional memories. Proceedings of the National Academy of Sciences, 99, 10789-10794.
  • Everhart, D.E., Shucard, J.L., Quatrin, T. & Shucard, D.W. 2001. Sex-related differences in event-related potentials, face recognition, and facial affect processing in prepubertal children. Neuropsychology, 15(3), 329-341.
  • Fallon, J.H., Keator, D.B., Mbogori, J., Taylor, D. & Potkin, S.G. 2005. Gender: a major determinant of brain response to nicotine. The International Journal of Neuropsychopharmacology, 8(1), 17-26. (see
  • Geary, D.C. 1998. Male, Female: The Evolution of Human Sex Differences. Washington, D.C.: American Psychological Association.
  • Haier, R.J., Jung, R.E., Yeo, R.A., Head, K. & Alkire, M.T. 2005. The neuroanatomy of general intelligence: sex matters. NeuroImage, 25(1), 320-327.
  • Hanlon, H. 2001. Gender Differences Observed in Preschoolers’ Emerging Neural Networks. Paper presented at Genomes and Hormones: An Integrative Approach to Gender Differences in Physiology, an American Physiological Society (APS) conference held October 17-20 in Pittsburgh.
  • Kempel, P.. Gohlke, B., Klempau, J., Zinsberger, P., Reuter, M. & Hennig, J. 2005. Second-to-fourth digit length, testosterone and spatial ability. Intelligence, 33(3), 215-230.
  • Lacreuse, A., Kim, C.B., Rosene, D.L., Killiany, R.J., Moss, M.B., Moore, T.L., Chennareddi, L. & Herndon, J.G. 2005. Sex, age, and training modulate spatial memory in the Rhesus monkey (Macaca mulatta). Behavioral Neuroscience, 119 (1).
  • Levin, S.L., Mohamed, F.B. & Platek, S.M. 2005. Common ground for spatial cognition? A behavioral and fMRI study of sex differences in mental rotation and spatial working memory. Evolutionary Psychology, 3, 227-254.
  • Lewin, C. & Herlitz, A. 2002. Sex differences in face recognition-Women's faces make the difference, Brain and Cognition, 50 (1), 121-128.
  • OECD. Learning for Tomorrow's World –First Results from PISA 2003,2340,en_2649_201185_34010524_1_1_1_1,00.html
  • Reed, T.E., Vernon, P.A. & Johnson, A.M. 2005. Confirmation of correlation between brain nerve conduction velocity and intelligence level in normal adults. Intelligence, 32(6), 563-572.
  • van Exel, E., Gussekloo, J., de Craen, A.J.M, Bootsma-van der Wiel, A., Houx, P., Knook, D.L. & Westendorp, R.G.J. 2001. Cognitive function in the oldest old: women perform better than men. Journal of Neurology, Neurosurgery & Psychiatry, 71, 29-32.
  • Witelson, S.F., Beresh, H. & Kigar, D.L. 2006. Intelligence and brain size in 100 postmortem brains: sex, lateralization and age factors. Brain, 129, 386-398.
  • Witelson, S.F., Kigar, D.L. & Stoner-Beresh, H.J. 2001. Sex difference in the numerical density of neurons in the pyramidal layers of human prefrontal cortex: a stereologic study. Paper presented to the annual Society for Neuroscience meeting in San Diego, US.

For more on this, see the research reports

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Menstruation doesn't change how your brain works

  • A largish study for its type indicates that hormonal changes during the menstrual cycle have no impact on working memory, multitasking ability, or cognitive bias.

A study involving 88 women, some of whom had endocrinological disorders, has found that, while some hormones were associated with changes across one menstrual cycle in some of the women taking part, these effects didn't repeat in the following cycle. In other words, there was no consistent effect of hormonal changes on cognition. This is not to say that some individuals might not be consistently affected, just that it doesn’t appear to be a general rule.

While the number of participants isn’t huge, it is considerably larger than is common in these sort of studies. The replication across two cycles is particularly important, since if the researchers had settled for just looking at one cycle, they would have concluded that there was an effect on cognition — as several studies have previously concluded. This more rigorous study suggests that earlier findings should be regarded with caution.

The study followed the women through two menstrual cycles. For the first cycle, 88 women participated; 68 women were re-assessed for a second cycle, to rule out practice effects and false-positive chance findings. Visuospatial working memory, attention, cognitive bias and hormone levels were assessed at four consecutive time-points across both cycles.

Of the initial 88, 58 had no endocrinological problems, 13 were diagnosed with endometriosis, 16 with polycystic ovary syndrome (PCOS) and one woman with hyperprolactinemia. Additionally, 12 women presented with obesity. Women were excluded if they were using oral contraceptives, had been pregnant or breastfeeding within the past 6 months, were using medication or had surgery which might interfere with endocrine parameters, had severe psychiatric or general diseases, worked irregular shifts, had menstrual or ovulation disorders except those investigated in the study, or showed any additional abnormality in hormonal parameters. Mean age was 30. Data from the subset of healthy women were also analyzed separately, confirming no difference in the findings. I would have liked the researchers to mention how the 68 women in the replication were selected, but I assume, after all their emphasis on methodological rigor, that they would have been careful to make sure there was no bias in that selection.

It should be noted, however, that the cognitive testing wasn’t exhaustive by any means — it’s possible that other cognitive aspects might be affected by hormonal changes. However, attention and working memory are the areas generally accused, and most likely to be noticed by an individual.

Of course, that’s the thing about attention and working memory — they’re very sensitive to a host of factors, including sleep quality and stress. So, we often notice that we’re not working at top gear, and we’re likely to look around for reasons. If we’re women, and it’s our period or just before it, we’re quite likely to attribute the reason to that. And it may be true in an indirect way — if we have pain, or sleeplessness, or are stressed, for example. What this study tells us, is that the changes in hormonal levels don't seem to consistently affect cognition.



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Intelligence & the brain

See also

Intelligence (research reports)

Older news items (pre-2010) brought over from the old website

Genes more important for IQ as children get older

Data from six studies carried out in the US, the UK, Australia and the Netherlands, involving a total of 11,000 pairs of twins, has revealed that genes become more important for intelligence as we get older. The researchers calculated that genes accounted for some 41% of the variation in intelligence in 9 year olds, rising to 55% in 12 year olds, and 66% in 17 year olds. It was suggested that as they get older, children get better at controlling (or perhaps are allowed to have more control over) their environment, which they do in a way that accentuates their ‘natural’ abilities — bright children feed their abilities; less bright children choose activities and friends that are less challenging.

Haworth, C.M.A. et al. 2009. The heritability of general cognitive ability increases linearly from childhood to young adulthood. Molecular Psychiatry, advance online publication 2 June 2009; doi: 10.1038/mp.2009.55

A gene that influences intelligence

A study involving more than 2000 people from 200 families has found a link between the gene CHRM2, that activates multiple signaling pathways in the brain involved in learning, memory and other higher brain functions, and performance IQ. Researchers found that several variations within the CHRM2 gene (which is on chromosome 7) could be correlated with slight differences in performance IQ scores, which measure a person's visual-motor coordination, logical and sequential reasoning, spatial perception and abstract problem solving skills, and when people had more than one positive variation in the gene, the improvements in performance IQ were cumulative. Intelligence is a complex attribute that results from a combination of many genetic and environmental factors, so don’t interpret this finding to mean we’ve found a gene for intelligence.

[1173] Edenberg H, Porjesz B, Begleiter H, Hesselbrock V, Goate A, Bierut L, Dick D, Aliev F, Kramer J, Wang J, et al. Association of CHRM2 with IQ: Converging Evidence for a Gene Influencing Intelligence. Behavior Genetics [Internet]. 2007 ;37(2):265 - 272. Available from:

Common gene version optimizes thinking but carries a risk

On the same subject, another study has found that the most common version of DARPP-32, a gene that shapes and controls a circuit between the striatum and prefrontal cortex, optimizes information filtering by the prefrontal cortex, thus improving working memory capacity and executive control (and thus, intelligence). However, the same version was also more prevalent among people who developed schizophrenia, suggesting that a beneficial gene variant may translate into a disadvantage if the prefrontal cortex is impaired. In other words, one of the things that make humans more intelligent as a species may also make us more vulnerable to schizophrenia.

[864] Kolachana B, Kleinman JE, Weinberger DR, Meyer-Lindenberg A, Straub RE, Lipska BK, Verchinski BA, Goldberg T, Callicott JH, Egan MF, et al. Genetic evidence implicating DARPP-32 in human frontostriatal structure, function, and cognition. Journal of Clinical Investigation [Internet]. 2007 ;117(3):672 - 682. Available from:

Closing in on the genes involved in human intelligence

A genetic study claims to have identified two regions of the human genome that appear to explain variation in IQ. Previous research has suggested that between 40% and 80% of variation in human intelligence (as measured by IQ tests) can be attributed to genetic factors, but research has so far failed to identify these genes. The new study has identified specific locations on Chromosomes 2 and 6 as being highly influential in determining IQ, using data from 634 sibling pairs. The region on Chromosome 2 that shows significant links to performance IQ overlaps a region associated with autism. The region on Chromosome 6 that showed strong links with both full-scale and verbal IQ marginally overlapped a region implicated in reading disability and dyslexia.

[382] Posthuma D, Luciano M, Geus E, Wright M, Slagboom P, Montgomery G, Boomsma D, Martin N. A Genomewide Scan for Intelligence Identifies Quantitative Trait Loci on 2q and 6p. The American Journal of Human Genetics [Internet]. 2005 ;77(2):318 - 326. Available from:

Damaged brains show regions involved in intelligence

Comparison of brain scans of 241 patients with differing degrees of cognitive impairment from events such as strokes, tumor resection, and traumatic brain injury, has correlated the location of brain injuries with scores on each of the four indices in the Wechsler Adult Intelligence Scale (WAIS), the most widely used intelligence test in the world. It was found that lesions in the left frontal cortex were associated with lower scores on the verbal comprehension index; lesions in the left frontal and parietal cortex were associated with lower scores on the working memory index; and lesions in the right parietal cortex were associated with lower scores on the perceptual organization index. A surprisingly large amount of overlap in the brain regions responsible for verbal comprehension and working memory may suggest that these two measures of cognitive ability may actually represent the same type of intelligence.

[1179] Gläscher J, Tranel D, Paul LK, Rudrauf D, Rorden C, Hornaday A, Grabowski T, Damasio H, Adolphs R. Lesion Mapping of Cognitive Abilities Linked to Intelligence. Neuron [Internet]. 2009 ;61(5):681 - 691. Available from:

When it comes to intelligence, size matters

The NIH MRI Study of Normal Brain Development now contains data from more than 500 children and adolescents from newborns to 18-year-olds, who had brain scans multiple times over a period of years as well as various cognitive tests. A sample of 216 healthy 6 to 18 year old brains from the dataset reveal that there is a positive link between cortical thickness and cognitive ability in many areas of the frontal, parietal, temporal and occipital lobes. The regions with the greatest relationship were the 'multi-modal association' areas, where information converges from various regions of the brain for processing. The finding supports a distributed model of intelligence.

[874] Karama S, Ad-Dab'bagh Y, Haier RJ, Deary IJ, Lyttelton OC, Lepage C, Evans AC. Positive association between cognitive ability and cortical thickness in a representative US sample of healthy 6 to 18 year-olds. Intelligence [Internet]. Submitted ;37(2):145 - 155. Available from:

Processing speed component of intelligence is largely inherited

A new kind of scanner used on the brains of 23 sets of identical twins and 23 sets of fraternal twins has revealed that myelin quality is under strong genetic control in the frontal, parietal, and left occipital lobes, and that myelin quality (in the cingulum, optic radiations, superior fronto-occipital fasciculus, internal capsule, callosal isthmus, and corona radiata) was correlated with intelligence scores. Myelin governs the speed with which signals can travel along the axons of neurons, that is, how fast we can process information. The researchers are now working on finding the genes that may influence myelin growth.

[1310] de Zubicaray GI, Wright MJ, Srivastava A, Balov N, Thompson PM, Chiang M-C, Barysheva M, Shattuck DW, Lee AD, Madsen SK, et al. Genetics of Brain Fiber Architecture and Intellectual Performance. J. Neurosci. [Internet]. 2009 ;29(7):2212 - 2224. Available from:

Intelligence and rhythmic accuracy go hand in hand

And in another perspective on the nature of intelligence, a new study has demonstrated a correlation between general intelligence and the ability to tap out a simple regular rhythm. The correlation between high intelligence and a good ability to keep time, was also linked to a high volume of white matter in the parts of the frontal lobes involved in problem solving, planning and managing time. The finding suggests that the long-established correlation of general intelligence with the mean and variability of reaction time in elementary cognitive tasks, as well as with performance on temporal judgment and discrimination tasks, is a bottom-up connection, stemming from connectivity in the prefrontal regions.

[665] Ullen F, Forsman L, Blom O, Karabanov A, Madison G. Intelligence and Variability in a Simple Timing Task Share Neural Substrates in the Prefrontal White Matter. J. Neurosci. [Internet]. 2008 ;28(16):4238 - 4243. Available from:

Brain network related to intelligence identified

A review of 37 imaging studies may have finally answered an age-old question: where is intelligence. Following on from recent evidence suggesting that intelligence is related to how well information travels throughout the brain, the researchers believe they have identified the stations along the routes intelligent information processing takes. These stations primarily involve areas in the frontal and the parietal lobes, many of which are involved in attention and memory, and more complex functions such as language. Basically, the researchers theorize that your level of intelligence is a function of how well these areas communicate with each other. It’s particularly interesting to note that these various imaging studies had remarkably consistent results despite the different definitions of intelligence used in them.

[1015] Jung RE, Haier RJ. The Parieto-Frontal Integration Theory (P-FIT) of Intelligence: Converging Neuroimaging Evidence. Behavioral and Brain Sciences [Internet]. 2007 ;30(02):135 - 154. Available from:

Intelligence based on the volume of gray matter in certain brain regions

Confirming earlier suggestions, the most comprehensive structural brain-scan study of intelligence to date supports an association between general intelligence and the volume of gray matter tissue in certain regions of the brain. Because these regions are located throughout the brain, a single "intelligence center" is unlikely. It is likely that a person's mental strengths and weaknesses depend in large part on the individual pattern of gray matter across his or her brain. Although gray matter amounts are vital to intelligence levels, only about 6% of the brain’s gray matter appears related to IQ — intelligence seems related to an efficient use of relatively few structures. The structures that are important for intelligence are the same ones implicated in memory, attention and language. There are also age differences: in middle age, more of the frontal and parietal lobes are related to IQ; less frontal and more temporal areas are related to IQ in the younger adults. Previous research has shown the regional distribution of gray matter in humans is highly heritable. The findings also challenge the recent view that intelligence may be a reflection of more subtle characteristics of the brain, such as the speed at which nerve impulses travel in the brain, or the number of neuronal connections present. It may of course be that all of these are factors.

[715] Haier RJ, Jung RE, Yeo RA, Head K, Alkire MT. Structural brain variation and general intelligence. NeuroImage [Internet]. 2004 ;23(1):425 - 433. Available from:

Brain size does matter, but differently for men and women

A study involving the intelligence testing of 100 neurologically normal, terminally ill volunteers, who agreed that their brains be measured after death, found that a bigger brain size is correlated with higher intelligence in certain areas, but there are differences between women and men. Verbal intelligence was clearly correlated with brain size, accounting for 36% of the verbal IQ score, for women and right-handed men — but not for left-handed men. Spatial intelligence was also correlated with brain size in women, but much less strongly, while it was not related at all to brain size in men. It may be that the size or structure of specific brain regions is related to spatial intelligence in men. Brain size decreased with age in men over the age span of 25 to 80 years, suggesting that the well-documented decline in visuospatial intelligence with age is related, at least in right-handed men, to the decrease in cerebral volume with age. However age hardly affected brain size in women.

[1029] Witelson SF, Beresh H, Kigar DL. Intelligence and brain size in 100 postmortem brains: sex, lateralization and age factors. Brain: A Journal of Neurology [Internet]. 2006 ;129(Pt 2):386 - 398. Available from:

Correlation between brain volume and intelligence

An analysis of 26 previous international studies involving brain volume and intelligence has found that, on average, intelligence (as measured by standardized intelligence tests) increases with increasing brain volume. The correlation was higher for females than males, and for adults compared to children.

[925] McDaniel MA. Big-brained people are smarter: A meta-analysis of the relationship between in vivo brain volume and intelligence. Intelligence [Internet]. Submitted ;33(4):337 - 346. Available from:

A copy of the study is available at

IQ-related brain areas may differ in men and women

An imaging study of 48 men and women between 18 and 84 years old found that, although men and women performed equally on the IQ tests, the brain structures involved in intelligence appeared distinct. Compared with women, men had more than six times the amount of intelligence-related gray matter, while women had about nine times more white matter involved in intelligence than men did. Women also had a large proportion of their IQ-related brain matter (86% of white and 84% of gray) concentrated in the frontal lobes, while men had 90% of their IQ-related gray matter distributed equally between the frontal lobes and the parietal lobes, and 82% of their IQ-related white matter in the temporal lobes. The implications of all this are not clear, but it is worth noting that the volume of gray matter can increase with learning, and is thus a product of environment as well as genes. The findings also demonstrate that no single neuroanatomical structure determines general intelligence and that different types of brain designs are capable of producing equivalent intellectual performance.

[938] Haier RJ, Jung RE, Yeo RA, Head K, Alkire MT. The neuroanatomy of general intelligence: sex matters. NeuroImage [Internet]. 2005 ;25(1):320 - 327. Available from:

Individual primates display variation in general intelligence

Research into cognition of non-human animals has been concerned almost entirely with the abilities of the species, not with individual variation within a species. Now a study of 22 cotton-top tamarins has revealed that these monkeys, like humans, also display substantial individual variation on tests of broad cognitive ability, although the degree of variation does seem significantly smaller than it is among humans (individual variability accounted for some 20% of the monkey’s performance, while it accounts for some 40-60% of human’s performance on IQ tasks). It may be that greater variability has been an important factor in human brain evolution.

[781] Banerjee K, Chabris CF, Johnson VE, Lee JJ, Tsao F, Hauser MD. General Intelligence in Another Primate: Individual Differences across Cognitive Task Performance in a New World Monkey (Saguinus oedipus). PLoS ONE [Internet]. 2009 ;4(6):e5883 - e5883. Available from:

Full text available at

Bigger is smarter: brain size predicts intelligence in different species

Animals with larger body sizes generally have larger brains, and it has generally been assumed that larger animals require larger nervous systems to coordinate their larger bodies. Consequently, comparison of brain size across different animal species, as an indirect measurement of intelligence, have controlled for body size. New research however suggests that, although some correction is probably needed, completely controlling for body size is almost certainly a mistake. Both overall brain size and overall neocortex size proved to be good predictors of intelligence in different primate species.

[998] Deaner RO, Isler K, Burkart J, van Schaik C. Overall Brain Size, and Not Encephalization Quotient, Best Predicts Cognitive Ability across Non-Human Primates. Brain, Behavior and Evolution [Internet]. 2007 ;70(2):115 - 124. Available from:

Size of brain areas does matter — but bigger isn't necessarily better

In a fascinating mouse study that overturns our simplistic notion that, when it comes to the brain, bigger is better, researchers have found that there is an optimal size for regions within the brain. The study found that if areas of the cortex involved in body sensations and motor control are either smaller or larger than normal, mice couldn’t run an obstacle course, keep from falling off a rotating rod, or perform other tactile and motor behaviors that require balance and coordination as well as mice with normal-sized areas could. It now seems that the best size in one that is best tuned to the context of the neural system within which that area functions — which is not really so surprising when you consider that every brain region acts as part of a network, in conjunction with other regions. This study builds upon a previous discovery by the same researchers, that a gene controls how the cortex in mice is divided during embryonic development into its functionally specialized areas. Different levels of the protein expressed by this gene changes the size of the sensorimotor areas of the cortex. It is known that significant variability in cortical area size exists in humans, and this may explain at least in part variability in human performance.

[334] Leingärtner A, Thuret S, Kroll TT, Chou S-J, Leasure LJ, Gage FH, O'Leary DDM. Cortical area size dictates performance at modality-specific behaviors. Proceedings of the National Academy of Sciences [Internet]. 2007 ;104(10):4153 - 4158. Available from:

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Bigger brains associated with domain-general intelligence

Analysis of hundreds of studies testing the cognitive abilities of non-human primates provides support for a general intelligence, and confirms that the great apes are more intelligent than monkeys and prosimians. Individual studies have always been criticized for not clearly ensuring that one species wasn’t out-performing another simply because the particular testing situation was more suited to them. However, by looking at so many varied tests, the researchers have overcome this criticism. Although there were a few cases where one species performed better than another one in one task and reversed places in a different task, overall, some species truly outperformed others. The smartest species were clearly the great apes — orangutans, chimpanzees, and gorillas. Moreover, there was no evidence that any species performed especially well within a particular paradigm, contradicting the theory that species differences in intelligence only exist for narrow, specialized skills. Instead, the results argue that some species possess a broad, domain-general type of intelligence that allows them to succeed in a variety of situations.

Deaner, R.O., van Schaik, C.P. & Johnson, V. 2006. Do some taxa have better domain-general cognition than others? A meta-analysis of nonhuman primate studies. Evolutionary Psychology, 4, 149-196.

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Alzheimer's gene worse for women

Analysis of data from more than 8,000 people, most of them older than 60, has revealed that, among the 5,000 people initially tested cognitively normal, carrying one copy of the “Alzheimer’s gene” (ApoE4) only slightly increased men’s risk of developing


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Calcium supplements not associated with increased cardiovascular risk in women

Contradicting some earlier studies, new research using data from the very large and long-running Nurses' Health Study has found that calcium supplement intake was not associated with a higher risk of cardiovascular disease in women.


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Gender affects cardiovascular risk in those with type 2 diabetes

Type 2 diabetes greatly increases a person's risk of developing cardiovascular disease, but a new study shows that cardiovascular risk factors such as elevated blood pressure and cholesterol levels differ significantly between men and women with diabetes.

The study, involving 680 diabetics, found that blood pressure and LDL cholesterol levels were significantly higher in women, and women were significantly less likely to have these factors under control. Some 17% of men had control of these factors, compared to 6% of women.


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Gender differences in level of the ‘language protein’

A rat study has found that infant males have more of the Foxp2 protein (associated with language development) than females and that males also made significantly more distress calls than females. Increasing the protein level in females and reducing it in males reversed the gender differences in alarm calls.

A small pilot study with humans found that 4-year-old girls had more of the protein than boys. In both cases, it is the more communicative gender that has the higher level of Foxp2.



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Males' superior spatial ability probably not an evolutionary adaptation

Evidence against an evolutionary explanation for male superiority in spatial ability coves from a review of 35 studies covering 11 species: cuttlefish, deer mice, horses, humans, laboratory mice, meadow voles, pine voles, prairie voles, rats, rhesus macaques and talastuco-tucos (a type of burrowing rodent). In eight species, males demonstrated moderately superior spatial skills to their female counterparts, regardless of the size of their territories or the extent to which males ranged farther than females of the same species.



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Menopause forgetfulness greatest early in postmenopause

January, 2013

A smallish study suggests that the cognitive effects of menopause are greatest in the first year after menopause.

Being a woman of a certain age, I generally take notice of research into the effects of menopause on cognition. A new study adds weight, perhaps, to the idea that cognitive complaints in perimenopause and menopause are not directly a consequence of hormonal changes, but more particularly, shows that early post menopause may be the most problematic time.

The study followed 117 women from four stages of life: late reproductive, early and late menopausal transition, and early postmenopause. The late reproductive period is defined as when women first begin to notice subtle changes in their menstrual periods, but still have regular menstrual cycles. Women in the transitional stage (which can last for several years) experience fluctuation in menstrual cycles, and hormone levels begin to fluctuate significantly.

Women in the early stage of post menopause (first year after menopause), as a group, were found to perform more poorly on measures of verbal learning, verbal memory, and fine motor skill than women in the late reproductive and late transition stages. They also performed significantly worse than women in the late menopausal transition stage on attention/working memory tasks.

Surprisingly, self-reported symptoms such as sleep difficulties, depression, and anxiety did not predict memory problems. Neither were the problems correlated with hormone levels (although fluctuations could be a factor).

This seemingly contradicts earlier findings from the same researchers, who in a slightly smaller study found that those experiencing poorer working memory and attention were more likely to have poorer sleep, depression, and anxiety. That study, however, only involved women approaching and in menopause. Moreover, these aspects were not included in the abstract of the paper but only in the press release, and because I don’t have access to this particular journal, I cannot say whether there is something in the data that explains this. Because of this, I am not inclined to put too much weight on this point.

But we may perhaps take the findings as support for the view that cognitive problems experienced earlier in the menopause cycle are, when they occur, not a direct result of hormonal changes.

The important result of this study is the finding that the cognitive problems often experienced by women in their 40s and 50s are most acute during the early period of post menopause, and the indication that the causes and manifestations are different at different stages of menopause.

It should be noted, however, that there were only 14 women in the early postmenopause stage. So, we shouldn’t put too much weight on any of this. Nevertheless, it does add to the picture research is building up about the effects of menopause on women’s cognition.

While the researchers said that this effect is probably temporary — which was picked up as the headline in most media — this was not in fact investigated in this study. It would be nice to have some comparison with those, say, two or three and five years post menopause (but quite possibly this will be reported in a later paper).


[3237] Weber MT, Rubin LH, Maki PM. Cognition in perimenopause. Menopause: The Journal of The North American Menopause Society [Internet]. 2013 . Available from:



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Large drop in IQ in those who smoked marijuana regularly as teens

September, 2012

Persistent marijuana use beginning before age 18 (but not after) is associated with a significant drop in IQ in a large, long-running study.

A large long-running New Zealand study has found that people who started using cannabis in adolescence and continued to use it for years afterward showed a significant decline in IQ from age 13 to 38. This was true even in those who hadn’t smoked marijuana for some years.

The study has followed a group of 1,037 children born in 1972-73. At age 38, 96% of the 1004 living study members participated in the latest assessment. Around 5% were regularly smoking marijuana more than once a week before age 18 (cannabis use was ascertained in interviews at ages 18, 21, 26, 32, and 38 years, and this group was not more or less likely to have dropped out of the study).

This group showed an average decline in IQ of 8 points on cognitive tests at age 38 compared to scores at age 13. Such a decline was not found in those who began using cannabis after the age of 18. In comparison, those who had never used cannabis showed a slight increase in IQ. The effect was dose-dependent, with those diagnosed as cannabis dependent on three or more occasions showing the greatest decline.

While executive function and processing speed appeared to be the most seriously affected areas, impairment was seen across most cognitive domains and did not appear to be statistically significantly different across them.

The size of the effect is shown by a further measure: informants (nominated by participants as knowing them well) also reported significantly more attention and memory problems among those with persistent cannabis dependence. (Note that a decline of 8 IQ points in a group whose mean is 100 brings it down to 92.)

The researchers ruled out recent cannabis use, persistent dependence on other drugs (tobacco, alcohol, hard drugs), and schizophrenia, as alternative explanations for the effect. The effect also remained after years of education were taken into account.

The finding supports the view that the adolescent brain is vulnerable to the effects of marijuana, and that these effects are long-lasting and significant.

Some numbers for those interested: Of the 874 participants included in the analysis (those who had missed at least 3 interviews in the 25 years were excluded), 242 (28%) never used cannabis, 479 (55%) used it but were never diagnosed as cannabis-dependent, and 153 (17%) were diagnosed on at least one of the interviews as cannabis-dependent. Of these, 80 had been so diagnosed on only one occasion, 35 on two occasions, and 38 on three or more occasions. I note that the proportion of males was significantly higher in the cannabis-dependent groups (39% in never used; 49% in used but never diagnosed; 70%, 63%, 82% respectively for the cannabis-dependent).



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