Why My Brain Size is Different from Yours: Biological Sex as a Factor

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Complicated-looking brain maps from today’s research article

I do brain outreach with children, meaning I go around to elementary and middle schools and teach about brain health, anatomy, and function. Without fail, someone always asks me about why some of the human brains we bring (donated to the university pre-mortem for the purposes of education) were smaller than others. Part of this is due to differences in how the brains were preserved but part of it is, I assume, due to how big the brain was to begin with. I would tell them this and would IMMEDIATELY remind them that just because a brain is bigger doesn’t mean it’s better because bigger people have bigger brains.

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Wrinkly bits seen here in this photo by Fred Hossler from the National Geographic website

Well that’s true and that isn’t true, apparently. According to the recent Science article, “Study Finds Some Significant Differences in Brains of Men and Women,” biological sex* might also play a factor. The gist of the article is that there are neuroanatomical differences between men and women in this sample of 5,216 citizens of the UK between the ages of 44 and 77. They looked at thickness of the cerebral cortex (cortex is the wrinkly stuff you think of when you think of a brain) and volume of 68 different “areas within the brain” (which I took to mean the areas of the brain underneath the wrinkly bits).

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Look at all those areas that aren’t wrinkly bits! (Thanks University of British Columbia for this excellent image)

According to Science (the magazine, not the systematic study of the structure and behavior of the physical and natural world through observation and experiment), the research found that men have bigger subcortical regions (all 68 of them the way it sounds) but women have thicker cortex. But then they tell me that when a bunch of statistical controls were done (which I feel like probably should have been done in the first place) 14 subcortical areas were larger in men and 10 were larger in women (If you’re thinking, “wait, I thought you said they were all larger in men?” then you and me both, my friend).

As always, I wanted to go to the source. This one was less easy to find because Science didn’t directly cite it for me (the nerve of them, amiright?).I looked up “Ritchie UK Biobank” in Google Scholar and this research article by Ritchie, Cox, Shen, Lombardo, Reus, Alloza, Harris, Alderson, Hunter, Neilson, Liewald, Auyeung, Whalley, Lawrie, Gale, Bastin, McIntosh, and Deary (science means never publishing a paper alone, apparently) was the only one that fit the description.

I read this one on a plane flight complete with TWO tiny bags of pretzels

 Article Summary

What they did: The UK has this thing called a Biobank, where biological data on the population is stored (all volunteers!). This study used the data from 2,750 women and 2,466 men. This data was collected by putting people in a really big magnet and getting pretty pictures of their brains, essentially. Then they took all those images and compared them between the sexes to see if there were any differences. They specifically looked at the volume of 7 subcortical structures (hippocampus, nucleus accumbens, amygdala, caudate nucleus, dorsal pallidum, putamen, and thalamus, in case you were interested) as well as the volume, surface area, and thickness of 68 cortical regions. They also looked at white matter tract directionality/complexity as well as functional connectivity, but as that is not discussed in the original online article and I’m trying to keep this to ~1,500 words, I won’t be discussing that in this blog post (I’ll find another paper specifically on things like that for you lovely people, don’t worry!)

What they found: They found a lot of things. Overall, men had larger brains, even accounting for their larger bodies. So when they tell me that all seven subcortical structures were larger in men than in women I’m thinking, ‘of course they are, men

Here’s a nifty table I drew of their results in case you needed a visual representation of the chaos.

have larger brains in general.’ When they finally decided to control for overall brain volume, the results were more interesting (and, I’d like to think, more accurate.) They found that of those seven structures, men actually only had three larger than women, and women had one larger than men (the nucleus accumbens, if anyone is interested).

At this point I’m a little annoyed because they dragged me through all this suspense of men having larger volumes of all these things when they don’t actually, but I kept reading because I love science and also because I had already wrote the first half of this post.

Let’s get onto those cortical areas. Without adjusting for overall brain size, ALL 68 areas were larger in men than in women. But, and this should surprise no one, when overall brain volume was taken into consideration, men had 14 larger areas than women and women had 10 larger areas than men, and 44 of those areas there were no significant differences. Thanks, statistics (see the image at the top of the page and look at the difference between the first and middle panel for a visualization of this). Men also had larger surface areas than women. I could not tell if this was the result controlling for overall brain volume or not. Don’t worry ladies, even if men have larger cortices by volume and surface area, our slightly smaller cortices are thicker. This was found in 47 areas of the brain unadjusted for brain size and still 46 areas when adjusted. So, go us for being consistent I guess?

Inner Skeptic:

I wanted to take a quick moment to point out that the online news release from Science got the subcortical and cortical areas confused (saying there were 68 subcortical regions looked at but also talking about their thickness). I wanted to remind people that copywriters, regardless of the scientific background, might not always get everything right which is why we need to think critically about each article we come across (including, for example, mine!)

I had a few issues with this paper. I think the largest issue is that it wasn’t actually a peer reviewed publication. I know this because it told me at the top of each page (see below). This doesn’t mean it’s not science, nor does it mean it can’t be good, but it does mean that it hasn’t been critically looked at by other scientists yet, and the results should probably be questioned a bit more than your average paper. I will be interested to see if they publish in a peer reviewed journal and how similar that paper will look to this one.


Second, I didn’t like that I had to read through all that crap about brain area sizes being different when the overall brain volume wasn’t accounted for. I felt like they should have just automatically done that and used those results as their only results.

Third, their age range was 44-77. This does not take into account a very large part of the population. It is also at the time when women are going through menopause which does things to their brains and bodies that no one understands because no one controlled for it in this study. This means the results might not be able to be generalized to the rest of the population.

Final Thoughts:

My first thought is that I should have chosen an article with fewer list-like results. But sometimes that doesn’t happen so I will forgive myself.

More importantly, brain size doesn’t necessarily mean anything with regard to intelligence or daily activities. Remember that. It’s not the same as smartness or talent or anything like that. It is simply a physical attribute unique to you as a person. Overall I think it’s a really interesting thing to look at, because women and men have different outcomes in psychiatric situations so it would be amazing if we could find a good underlying reason for that. They weren’t able to do that in this study (which was never meant to be anything more than descriptive, according to the author), but if you want to go get a bunch of brain images and measure volume/surface area/thickness against different psychiatric disorders, I’m sure there’s a pretty sum of grant money in it for you.

 

*Because the study in question did not take into account gender versus biological sex, and did not discuss intersex, this is going to be about biologically male vs biologically female brains with complete disregard to whether a participant’s gender lines up with their sex.

Have a science news article you want a closer look at? A concept you want to learn more about? Leave it in a comment or email us at phteatime@gmail.com!
About the author
14595564_10155083719871840_4974523626401782470_nMari is a graduate student studying psychology and neuroscience at the University of Minnesota. Her research focuses on affective, behavioral, and molecular aspects of opiate addiction. Mari loves all science and wants everyone else to be as excited about it and as critical of it as she is.
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Tea May or May Not Lower Your Risk of Developing Dementia Later in Life

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This is the first in our new series of blog posts looking into current and past scientific research and scientific concepts that are often misinterpreted or generally misunderstood. The goal of this blog series is for us as scientists and writers to struggle through articles and research so that you don’t have to. If you have a science news piece you’ve read, a concept you want to know more about, or general science questions, email them to phteatime@gmail.com and you might see your topic in a blog post! 

To begin our new blog series, I wanted to talk about this article that I came across recently on Facebook. It was posted by a neuroscience research page that I follow, and also it’s about tea. I ADORE tea (and neuroscience), so of course I had to read it and subsequently tell the world about it.

The gist of the article is that drinking tea every day may help fend off cognitive decline as we get older and decreases the risk of developing dementia and Alzheimer’s disease. If this is true, then this is HUGE. Alzheimer’s Disease is a devastating neurodegenerative disease that affects a lot of people and comes with some pretty severe memory, mood, and physical issues. As someone who has had a family member die from Alzheimer’s Disease, I’m always on the look out for research that has found a cure. As a neuroscientist, though, I’m always skeptical.

So let’s look a little more closely at the research that this article is citing. First, I went to the original National University of Singapore news release (found here). It begins, “A cup of tea a day can keep dementia away,” (what a freaking amazing first sentence, am I right?) before proceeding to describe the study and how drinking tea every day can lower the risk of cognitive decline in older age. This is pretty similar to the article that cited it–similar enough to make me question how plagiarism works in the news.

At this point I’m reaching for my tea kettle, partly because I adore tea but also partly because I don’t want to develop Alzheimer’s Disease. But then I realized that as a skeptic I should probably go to the original article to see what’s up.

Proof that I not only read this paper but was drinking tea the whole time

I realize not everyone has access to articles the way I do because I’m a graduate student and my university pays an enormous amount of money for access to academic journals. I don’t know how illegal it is for me to share the PDF, but here it is if you’re interested and please no one report me to the feds: Tea consumption reduces the incidence of neurocognitive disorders: Findings from the Singapore longitudinal aging study (a catchy title, I know). If reading academic articles makes your brain hurt, you’re not alone. In theory I’ve been doing this for years and should be able to understand many types of academic articles well enough to breeze through them. In practice, different fields of science have such vastly different ways of describing their experiments, peppered with mass quantities of jargon and–god forbid–mathematical models specific only to that field. So don’t worry, I’ve already struggled through it for you and here’s what it says and what I thought:

Article Summary:

What they did: 957 Singaporeans 55 years or older participated in this study. They had normal cognitive functioning between 2003-2005 (measured through something called the Mini Mental State Exam, which is legit according to my clinical psychologist friends). During those years, participants answered questions about their tea drinking habits: how often did they drink tea and what type of tea did they drink? The options for types of teas were “Ceylon/English” tea aka black tea, “Chinese tea” which I think is oolong, and “Green” tea which–correct me if I’m wrong–refers to green tea. They also asked for gender (male or female, in this case) and whether participants had a specific allele of a gene that is a risk for developing Alzheimer’s disease (an APOEε4 gene, if you’re interested). Finally, they looked at incidence of developing a “neurocognitive disorder” such as Alzheimer’s disease between 2006 and 2010 (72 of the participants fell into this category). They controlled for a bunch of variables, too, like BMI, whether people smoked, education, age, etc, to try to only be looking at the effect of tea.

What they found: This is where it gets cool. They did some magic stats (not really, they did some two-sided Chi-square tests and logistic regression models) where they looked at whether drinking tea was associated with a lower incidence of neurocognitive disorders at their later time point. They did this first with just tea as their comparison and then also while controlling for a bunch of other variables (education level, alcohol consumption, physical activity, etc.) that also might have an effect on cognition. They partly control for other variables because they want to make sure they’re testing JUST FOR TEA, but also because their groups had some baseline differences in these measures so we need to put them into our statistical models in an effort to say, “if I hold this constant, does tea still have an effect.”

Guys, it totally does. They found that the group with consistent tea consumption throughout the experiment (can be black, oolong, or green) had a much lower incidence of neurocognitive disorders (aka percentage of people who developed neurocognitive disorders) later on. This protection, however, is ONLY for women and maybe also (but the stats aren’t sure) for people with that APOE risk allele we talked about earlier. So men without an APOE risk gene, you don’t have extra protection (but good job on not having a risk allele, I guess?) but can still enjoy tea for it’s other helpful properties like attention or alertness.

So ladies (and everyone with an Alzheimer’s risk allele), go forth and buy tea.

Inner Skeptic:

Let’s talk about how to look at this paper critically. I’ll go through just a few of my thoughts (not all of them but some). First, there were some big baseline differences between tea drinkers and non-tea drinkers in 2003-2005. Does this mean these two groups of people are fundamentally different other than their tea drinking? Are there separate factors that drive both tea drinking AND a lower chance of neurocognitive disorders? Maybe. Science is hard and we can’t always control for every little thing. These guys actually did a pretty good job with what they had to work with. I’ll give them the benefit of the doubt.

Also, what about white tea? I love me some white tea and I keep hearing about how good it is for you. How am I supposed to know if these claims are real if science doesn’t include it? I assume it wasn’t included because white tea isn’t as prominently imbibed in this participant pool. Still would have loved to see it.

Finally, and they say this in their discussion section, statistical power is better with more participants, and they didn’t have as many as they wanted in some of their groups (like green tea only drinkers) which makes it hard to say for sure whether this is real or whether it’s by chance because we have a small population. It’s a pretty big group of people and the oolong/black tea group is definitely large enough to show support for tea drinking, but to be certain it would be nice to see more participants in the future.

Final Thoughts:

Let me start by just saying that tea is delicious and cozy and perfect so you may as well drink a cup every day. But also tea may or may not decrease your risk for developing a neurocognitive disorder when you get older. So, best casenario, you fend off dementia. Worst casenario, you drink delicious tea your whole life.

I’m hoping to see future studies looking at the underlying reasons for this protective effect. They mention the components of tea that they think are at play, but, you know, I want to see concrete evidence and all that jazz.

Have a science news article you want a closer look at? A concept you want to learn more about? Leave it in a comment or email us at phteatime@gmail.com!
About the author
14595564_10155083719871840_4974523626401782470_nMari is a graduate student studying psychology and neuroscience at the University of Minnesota. Her research focuses on affective, behavioral, and molecular aspects of opiate addiction. Mari loves all science and wants everyone else to be as excited about it and as critical of it as she is.