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The incredible shrinking hippocampus (and how to stop it)

September 27th, 2011

Over the last few years, a bunch of studies have built the case that aerobic exercise does something to keep your brain in good working order as you age — or perhaps more accurately, it does several good things for your brain. Last week, I blogged about a study showing that exercise stimulates the growth of new mitochondria in the brain. In the comments of that post, Seth Leon pointed out another new study — this one in the September issue of Neuropsychology — that links exercise to greater volume of the hippocampus, which in turn improves memory.

I’ve been particularly interested in the hippocampus ever since I wrote this article in The Walrus back in 2009, looking at suggestions that increased use of GPS navigation would lead to decreased volume of the hippocampus, where our direction-finding skills reside. And smaller hippocampi are associated with increased risk of age-related cognitive impairment. One of the researchers I spoke to worried that this is part of larger shift:

But Bohbot sees the decline in spatial thinking as part of a broader shift toward stimulus-response, reward-linked behaviour. The demand for instant gratification, for efficiency at all costs and productivity as the only measure of value — these sound like the laments of the nostalgist in the Age of the Caudate Nucleus. But here, they’re based on neuroscience. “Society is geared in many ways toward shrinking the hippocampus,” she says. “In the next twenty years, I think we’re going to see dementia occurring earlier and earlier.”

I can’t count the number of times I’ve taken wrong turns since writing that article because of my stubborn refusal to use GPS unless absolutely necessary! But I digress…

Anyway, this new study, by researchers at the University of Illinois, looked at a group of 158 sedentary adults between 60 and 80 years old, to look for evidence for the following model:

The basic gist is straightforward: they hypothesize that fitness (as measured by a graded exercise test to exhaustion) predicts hippocampus size, which in turn predicts working memory, which in turn predicts how frequently you forget things. What’s new about this study is that they separately consider age, BMI, sex, physical activity, and education to see if any of them are skewing the results. Here’s what they find:

By and large, the data supports their hypothesis. There are a few wrinkles: for example, age, in addition to affecting fitness, also has a direct effect on hippocampus size. That means no matter how fit you are, your hippocampus is still getting smaller. Also, physical activity (that’s the PASE box) didn’t directly contribute to fitness — but that’s not surprising, because the volunteers had to be sedentary in order to be admitted to the study, so they all had roughly the same (lack of) physical activity.

Bottom line: aerobic fitness is good for the brain — and in particular, it’s good for the hippocampus. So maybe if I get enough exercise, I’ll start letting myself use that GPS navigation system.

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  1. September 27th, 2011 at 11:47 | #1

    I am new to your blog and love it.
    I don’t know if you remember some years ago there was a lot of talk about London cab drivers whose hippocampi (?) were measured quite a bit larger than average. They have to undergo rigorous testing on their knowledge of the city before they are licensed. I need to ditch my GPS. :) That and running and I am all set, right?

  2. Gladys Ulrich
    September 27th, 2011 at 15:01 | #2

    I am a 78 (soon to be 79) female. I started walking two years ago; at first a half mile with huffing and puffing. I now do a 3 mile fitness regimen daily following an exercise program on disk. I’m doing this with my weight in mind. Recently, I’ve become enamored with the thought that I’m doing good for my brain. I enjoyed this article. However, my GPS and I are still buddies.

  3. Seth Leon
    September 27th, 2011 at 16:36 | #3

    Thanks for posting the path results.

    I am a bit confused however as to the direction of some of the path coefficients. There is a direct negative effect of hippocampal volume on spatial memory RT (-.21)? That seems counter-intuitive unless RT represents memory lost. But then spatial memory RT also has a direct negative effect on the frequency of forgetting?

    The direct positive effect of fitness on hippocampal volume is clear and intuitive. The direct effect of hippocampal volume on frequency of forgetting is small but positive suggesting that the frequency of forgetting is really a measure of reduction in forgetting (more volume -> more reduction).

    With that assumption I guess the indirect path is that more hippocampal volume -> less spatial memory loss ->more reduction in forgetting which would make sense.

    I’m to cheap to pay to see how they defined the measured path variables. It seems encouraging that although there is a direct negative effect of age on hippocampal volume (-.22), the direct positive effect of fitness is stronger ( 0.39).

  4. September 28th, 2011 at 11:24 | #4

    Is this perhaps a reason why walking a race course prior to running it is helpful during the race? Walking (or driving) a course prior to running it would allow us to use the less demanding and faster stimulus-response a bit easier instead of worrying about where we are going?

  5. marcj
    September 28th, 2011 at 15:36 | #5

    Seth: my guess is that RT here means reaction time, where low scores are better. So the idea is that there’s a negative correlation wherein bigger hippocampi yield faster (= smaller) reaction times, hence the predicted negative correlation.

    More generally note that the “Spatial memory” box is a bit of a misnomer – it’s a measure of spatial working memory, which involves both short-term retention of a spatial scene, and its immediate manipulation. It’s not the same as things like navigation or memory of where you left your car keys, which is long-term memory. This study only finds a modest relationship between spatial WM and long-term spatial memory, so there are quite a few jumps to make between having a sedentary lifestyle and maintaining good long-term spatial memory.

  6. Seth Leon
    September 28th, 2011 at 20:56 | #6

    Ahh reaction time. That makes sense.

    Thanks marcj !

  7. Sarah
    October 27th, 2011 at 00:02 | #7

    I would love to discuss this more but…my hippocampus is full.

  1. September 28th, 2011 at 00:10 | #1
  2. October 21st, 2011 at 10:46 | #2