gender

Estrogen's effect on memory & learning

Estrogen's effect on the brain is a complex story, one which we are only beginning to understand. We know it's important for women, but we're not sure about the details. One of the problems is that it appears to interact with stress. There are two aspects to estrogen's effects on women: normal monthly fluctuations in estrogen levels, and menopause.

It's also important to distinguish post-menopause (once you have completely stopped menstruating) from perimenopause (the years of menstrual irregularity leading up to this).

In general, the last few years of research seem to be coming to the conclusion that any cognitive problems women experience as they approach menopause is limited, both in time and in task, and depends in part on other factors. For example, those who experience many hot flashes may have poorer verbal memory, but the main cause for this may be the poorer sleep quality; those who are distressed or experience mood changes may find their memory and concentration affected for that reason.  These findings suggest the best approach to dealing with cognitive problems in perimenopause is to tackle the physical and/or emotional causes.

Post-menopause is different. Post-menopause is all about low estrogen levels, and the importance of estrogen for brain function. Nevertheless, estrogen therapy for postmenopausal women has had inconsistent results; there has even been some research suggesting it may increase the risk of later dementia. There is also some suggestion that it may not help those women who have cognitively stimulating environments, or are highly educated. And other indications that timing might be critical -- the age at which you begin hormone therapy. At the moment, we simply have too little clear evidence to warrant recommending hormone therapy for cognitive reasons (particularly in light of the possible cancer risk), or to know when it might be effective.

Excitingly, however (because there is no downside!), there is some evidence that physical exercise can counter the cognitive decline postmenopausal women may experience. There's also a study suggesting that the effect of low estrogen after menopause is not to impair cognition but simply to change it -- however, because women aren't prepared for, or understand, these changes, they perceive it as impairment. That would suggest that what is needed is an education program in how the brain changes (but first we have to understand exactly how it does change!).

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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 (http://www.opinionjournal.com/la/?id=110006356 ), 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 http://education.guardian.co.uk/gendergap/story/0,7348,1393079,00.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: http://education.guardian.co.uk/higher/research/story/0,9865,1399109,00.html

Parts of this article originally appeared in the January and February 2005 newsletters.

References: 
  • 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 http://www.eurekalert.org/pub_releases/2005-02/uoc--bao021705.htm)
  • 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 http://www.oecd.org/document/0/0,2340,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.

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 MCI or Alzheimer’s — but nearly doubled women’s risk (healthy men with APOE4

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.

http://www.eurekalert.org/pub_releases/2014-05/bawh-csn050914.php

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.

Improving academic performance with a simple psychological intervention

Classroom image

Stereotype threat is a factor not only for some ethnic groups, but for women in certain areas (e.g., math, engineering), and also for older adults. Interventions that help reduce stereotype threat are also potentially helpful for those who suffer from test anxiety, or math anxiety.

Dave Nussbaum talks in the Scientific American about research he’s been involved in, showing how a small intervention aimed at reducing stereotype threat had significant long-lasting benefits for Latino American middle school students.

Gender differences in level of the ‘language protein’

Foxp2 gene

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.

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.

Menopause forgetfulness greatest early in postmenopause

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).

Reference: 

[3237] Weber, M. T., Rubin L. H., & Maki P. M. (2013).  Cognition in perimenopause. Menopause: The Journal of The North American Menopause Society.

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

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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