Are Men’s Brains Just Bigger?

By Neuroskeptic | September 25, 2013 5:22 am

The comparative anatomy of male and female brains is an incredibly popular topic. From teachers to cartoonists, everyone’s interested in it.

One supposed dude-dame dimorphism is the width of the corpus callosum, the white matter bridge that connects the brain’s left and right hemispheres.

Some studies suggest that women have a larger corpus callosum, relative to overall brain size, than men. This has led to a lot of speculation about how females, with their more ‘interconnected’ brains, are therefore better at things like multitasking:

The corpus callosum is 30 percent more highly developed in the female brain… allowing information to flow more easily from one side of the brain to the other, which allows a woman to focus on more than one thing at a time.

However, according to Eileen Luders and colleagues, that’s all a wash, because: Differences in Brain Volume Account for Apparent Sex Differences in Callosal Anatomy

It’s been argued that women’s relatively larger corpus callosa may reflect the fact that men have larger brains, on average, and that the corpus callosum is relatively smaller in larger brains. In other words, the corpus callosum difference might be a side-effect of the true gender difference (perhaps the only one) – bigger male brains overall.

Luders et al confirmed this with a clever technique: they looked in a large online brain database to find some extremely small male brains, and extremely large female ones. This, the two genders were matched on total size.

There was no gender difference in the corpus collosa of these equally-sized brains, as measured using ‘surface-based mesh-modelling':

The slight differences that did emerge were in the ‘wrong’ direction: men had thicker corpus callosum.

In fact, this is not so unusual, because quite a lot of previous studies have shown relatively larger corpus callosa in males. The bigger-in-males findings, however, never ‘went viral’ – perhaps because, unlike the bigger-in-females results, they don’t form a ready lightning rod for pre-existing half-conscious ideas about gender.

Still, anatomy aside, there are now claims that women’s brains are better connected functionally

ResearchBlogging.orgEileen Luders, Arthur W. Toga, & Paul M. Thompson (2013). Why Size Matters: Differences in Brain Volume Account for Apparent Sex Differences in Callosal Anatomy Neuroimage DOI: 10.1016/j.neuroimage.2013.09.040

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  • Klae A. Klevenger

    While this is an extremely awesome article about debating some information. Neuroskeptic should know when they write male and female at the beginning they acts as if they are talking about gender. They would be incorrect. Male, Female, and Intersex are the Sex we are born with. Man, Woman, Effeminate man, Masculine woman, Dee, Tom, Kathoey are gender identities. Gender is how you feel not how you are born. They start using gender as sex but using correct sex terms. Then in the last paragraph They switch to women instead of females.This is a great article but it needs to be reworded so that it is actually coherent. Did they look at people who identified as two “opposite” genders or did you mean two “opposite” sexes. Do you mean people who identify as women can do 2 things at once and are better connected functionally? Or did you mean females? Check your article then it will be worth the read.

    • Buddy199

      PC smack down

      • Klae A. Klevenger

        It’s not PC. Its a Lexicon. If you don’t know what you are actually discussing, how can you actually discuss something. When this article is read with correct knowledge of sex vs. gender you don’t actually know what is actually being discussed. Therefor it has nothing to do with being PC. But everything to do with science being done by people who actually understand the lexicon they are using. If you don’t understand the lexicon you are using you end up saying nothing. To me this article reads about males and females and their gender determining the size of their brains. Which I do not believe is the actual statement this person is saying. Because then a male who Identifies as a woman fucks up your whole understanding of what this article is about. Please fix the article. you are making yourself look uneducated.

        • Chaorder Gradient

          the argument is that the genetic definition of a sex is related to brain size. This is in no way confusing, and outside gender studies, male/female, and man/woman are used interchangeably in standard language.

          If you wan’t to posit a line between an anatomical differential of brain size and gender identity, then fine, but that is not what is being talked about here.

          • Klae A. Klevenger

            I beg to differ. Look up the definition of male and female and it talks of birth sex. Look up men and women and you get social constructs. It doesn’t matter what how the uneducated talk. If you copy them you sound just the same, uneducated. The only thing being talked about here is the differential of brain size and gender Identity.

            “In other words, the corpus callosum difference might be a side-effect of the true gender difference”

            “This, the two genders were matched on total size (perhaps the only one) – bigger male brains overall.”

            This sentence doesn’t even technically make sense. In fact it leads me to believe the writer believes they are talking about gender.

            “It’s been argued that women’s(gender) relatively larger corpus callosa may reflect the fact that
            men(gender) have larger brains, on average, and that the corpus callosum is relatively smaller in larger brains”

            “There was no gender difference in the corpus collosa”

            “men had thicker corpus callosum”

            When is sex being talked about? Besides the beginning with male and female and then in another paragraph. If you take the definition from the text you come up with male and female as gender. This is incorrect. If the author doesn’t have the mind to change it they are no scholar I would ever read again.

          • Klae A. Klevenger

            I would like to know how you know this article talks about he sexes when it mainly uses gender identifiers.

          • Josh

            Males have one Y chromosome and one X chromosome, while females have two X chromosomes. That is the scientific defenition of male and female being discussed here.

    • Neuroskeptic

      Well, since all of the participants in these studies were cisgender (AFAIK), the two are equivalent in this case.

      • Klae A. Klevenger

        How nice of you to mention now, not in your article, that these participants were cisgender. I would like to see where the participants identified as cisgender. Or you could just change all the gender identifiers to sex identifiers and then the whole article doesn’t need to know if they were cisgender and you don’t look like your making assumptions which is bad science.

      • Klae A. Klevenger

        As well saying they are cisgender still makes this article about gender and not sex. Because you didn’t take into account males and females who are not cisgender. Which is a bad representation of the sexes.

        • Dorkus Americanus

          You obviously have an entirely different topic in mind. Why don’t YOU write an article about that?

          • Klae A. Klevenger

            The article is titled about gender and then changes subject to sex in the first line. Changing back and forth from two different subjects is not a coherent blog about the topic.

            That’s not hard to see. You may not understand the difference doesn’t mean I have a different topic on mind. I originally asked that the language be corrected so I could understand the actual study. I don’t understand why a big deal had to be made about me asking for the article to use correct definitions. Male and female for sex. Men and Women for gender. Therefore there is no confusion. That is why we, as scientists, make definitions.

    • Alejandro Escudero

      New definition then…Let God know about it. :-)

      • Klae A. Klevenger

        What definition is new? Webster sure knows those definitions. Then again god knows donkeys and snakes can talk. Which I haven’t seen proven yet. So guess what. God doesn’t belong in a place of science. So go else where unless you are going to have an actual discussion instead of hide behind an old novel.

        • Dorkus Americanus

          You totally started it.

    • Dorkus Americanus

      This article is for lay people interested in science. For fun. It’s not a research paper being submitted for publication for academic reasons. The language was fine. Calm down.

      • Klae A. Klevenger

        According to the neuroskeptic they do not dumb down, therefor this is not lay language.

        • Neuroskeptic

          You’re quite right! I do not dumb down. I just undo over-complication…

          So I stand by everything I wrote and I would use the same language in an academic paper (in fact I’m pretty sure that I have used male/men female/women interchangeably in my academic papers.)

          In the context of this neuroscience post about this paper, it is perfectly acceptable. Most people accept it, and most writers of similar pieces do it.

          There may be contexts where it would not be correct. But I do not think this is one of them.

          • Klae A. Klevenger

            I’m sorry if you can somehow understand neuroscience when it is too overcomplicated to understand the difference between gender and sex.

            Please let the ridiculousness of that sink in.

            Yep, it’s too hard to understand that when you say Women you include MtF individuals. When you say Female you are only talking about individuals born with a vagina. I don’t see how that is over complicating anything. I would hope you could understand definitions that were set down so we know who and what you are talking about. But I see you don’t actually understand or else you wouldn’t have titled this paper with the word Gender then used sex identifiers for most of it. If were looking for gender differences I would look here and get horrible information because this is actually an article on sex differences. It is a big deal because they are not the same and I ask you as a scientist to learn the difference before you give people the wrong impression of your subject.

          • Klae A. Klevenger

            As well I would say it over complicates your blog to use words as synonyms when they are in fact not synonyms.

          • Klae A. Klevenger

            Might I remind you that sex ed is taught to elementary school children. Therfore everyone should know the difference between gender and sex. As well, any life science text issued in college usually mentions the definition of the biopsychosocial model which tells us that sex is bio and gender is social. Sorry but you learned the info please use it. nless you are a one-minded unidirectional believer, then there is obviously no hope.

  • Buddy199

    Interesting article but neuro-anatomical studies like these always strike me as one step removed from phrenology.

  • Thalestris

    “Dude-dame dimorphism” is a wonderful turn of phrase.

    (Finally, do you know if men’s skulls — and, by extension, brains — are bigger than women’s if matched with women of the same height and build? I’d like to know that, just for idle curiosity’s sake.)

  • Matt Baen

    I think a lot of the literature on male-female differences in brain structure and cognitive abilities are going to go the same way as that on races differences: into the rubbish bin. Good riddance to it. There’s a big backlash against pat neurocogntive pronouncements in general. I guess Jonah Lehrer ended up doing some good after all.

    A lot of this stuff is whispy, chocolate cookie graph stuff, or simply the wrong questions are being asked. Then there is the failure of allometric control – no, not just body weight but specifically tissue under the brain’s motor control and/or provide more sensory input. That would be harder than simply plugging in weight or height, when that’s even done at all. Plus brain size and brain structure fetishism is misplaced in the first place – though tempting because more sophisticated connectionist models are harder to investigate.

  • Magoonski

    If we want to prove that women are equal we need to stop covering up the history of their contributions. We don’t need b.s. things like ‘multitasking’ or the brain connection thing to make women seem capable, the proof is already there, we just need to put it in the history textbooks.

    • Jay Nomer

      While I do agree about the B.S part, what followed is just P.C nonsense. Female contribution to sciences is very small and entirely comprised of empirical work (ie: not works of genius). I don’t mean this in any derogatory manner.

      One of the greatest source of scientific history is the Dictionary of Scientific Biography (DSB), an incredible undertaking that has recently been updated to 26 volumes. When the biographies were originally compiled, it went through considerable pressure to include those other than “dead white males” into its roster.

      The new version was edited by Noretta Koertge, co-author of the “Professing Feminism” series that exposed Women’s Studies/Gender Studies as not fitting the standards of education. However, the fact that she was involved at all may point to some feminist tampering in the new edition and as such I’d advise caution to anyone using the new editions as reference.

      • Dorkus Americanus

        I think it’s important to note that the lack of comparative female contributions may, in large part, have been due to lack if access, and continued social prejudices against women in the sciences.

      • Magoonski

        I’ll admit that I doubt one would find a 50/50 mix but it would be nice to see more than Marie Curie in a textbook (I recommend Ada Lovelace and Anna Botsford Comstock to start).
        I admit I’ve never heard of the DSB before but I’m still going to take a shot in the dark and argue that perhaps the reason it’s not so full of women is because most women were assistants. Back in the 1800’s, schools for girls would have chemistry demonstrations for the public because back then boys were expected to learn literature and philosophy (just like pink was originally a color for baby boys). There were very few jobs that would take women on as assistants because women were expected to be ‘in the home,’ but what they would get would be clerical, surveying type positions (is that what you meant by empirical?). Henrietta Swan Leavitt would have been a great astronomer if she would have been allowed to use the telescope but the best she could get was helping Hubble with his discoveries. Society always screws women over and women are more prone to wanting to be accepted by society so it’s a double-edged sword.

    • Dorkus Americanus

      Multitasking! Ya know, for secretarial work! Just another way to keep women under that glass ceiling.

  • petrossa

    The vast difference between female aspergers and male aspergers is significant indicator something is really different in the CC

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  • Dennis

    wow, comparing size-matched brains seems to me like the most straight-forward thing one could come up with. o.O

    • Neuroskeptic

      It’s very elegant – size-matched brains are difficult to find though!

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  • PsychBrief

    I came across this paper today (though it’s by no means new) and was wondering what your thoughts were with regards to the differences between males and females. This paper found that even when controlling for brain size, females still had a larger corpus callosum, especially for young adults (p<0.0005). The overall difference only just reached statistical significance (p<0.03). The study had a reasonable sample size. It's not as elegant an experiment definitely but I'm curious as to your thoughts. Does the literature further support the idea that the corpus callosum is only different in size due to the differences in total volume, or has it shifted back towards there being a genuine difference (regardless of size)?

    • Neuroskeptic

      Hmm, interesting. That does seem like a good paper. It wasn’t discussed in the Luders et al. paper.



No brain. No gain.

About Neuroskeptic

Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.


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