8 ms·

Perhaps people who are either predisposed toward unhealthy outcomes, or are currently experiencing them (whether they realize it or not) are more sedentary. Cor

Perhaps people who are either predisposed toward unhealthy outcomes, or are currently experiencing them (whether they realize it or not) are more sedentary. Correlation does not establish causation.

callesgg 8y ago
Um yes, the title should be more like: "Sitting correlates to Thinning in certain brain regions"
- nonbel 8y ago
  Is it bad to have a "thin" brain and good to have a "fat" brain now? Can't this brain region become too large? What if the area is enlarged due to inflammation/swelling and these people with "thinning" are those without that problem? If the brain is too large it is considered a problem: https://en.wikipedia.org/wiki/Megalencephaly https://en.wikipedia.org/wiki/Megalencephaly This guy apparently has the second largest brain ever measured, and he was a serial killer: https://en.wikipedia.org/wiki/Edward_H._Rulloff https://en.wikipedia.org/wiki/Edward_H._Rulloff
  - MikkoFinell 8y ago
    The study was regarding density, not size.
    - nonbel 8y ago
      Where are you seeing that? Also, fine density/volume/mass, does it really change the argument? There is some optimal size for this region when it comes to certain functions, probably relative to the size of other regions. That size is probably suboptimal when it comes to other functions and there are tradeoffs going on. The press release seems to be assuming that thinner is bad automatically.
      - MikkoFinell 8y ago
        Yeah I do believe it makes a difference, because brain atrophy is linked to a range of cognitive impairments, for example strongly correlated with Alzheimer's disease. But you're right on the last point though, about assuming thinner is bad automatically. Heavy and chronic cannabis usage has been linked to an increase in density, but a reduction in total volume, which resulted in a slight overall decrease in IQ. The takeaway from all this being: Cognitive function is affected by a variety of parameters and we got more neuroscience to do still.
        nonbel 8y ago
        >"Heavy and chronic cannabis usage has been linked to an increase in density, but a reduction in total volume, which resulted in a slight overall decrease in IQ." I wouldn't put much stock into these type of non-quantitative explanations wherein "this makes that go up which makes this go down", etc. Usually the researchers measure a bunch of different things, analyze the data in a bunch of different ways, and only publish whatever is "significant". This works at the single lab level and multi-lab level since the "non-significant" results are considered boring and don't get published. By "usually" I mean this is standard behavior. You can call it p-hacking, file drawer effect, and more recently "forking paths": http://andrewgelman.com/2017/12/29/forking-paths-plus-lack-theory-no-reason-believe/ http://andrewgelman.com/2017/12/29/forking-paths-plus-lack-t... >"Cognitive function is affected by a variety of parameters and we got more neuroscience to do still." Sure, that was the case before these studies were done too though.
      - always_good 8y ago
        > The press release seems to be assuming that thinner is bad automatically. Well, it's not unreasonable. I don't know of any literature that says that a sedentary lifestyle is healthy for the brain, but a lot of it has found the opposite. I would like to avoid anything that reproduces the neurological effects of being sedentary.
        nonbel 8y ago
        >"I don't know of any literature that says that a sedentary lifestyle is healthy for the brain" Here are two I found: >"More sedentary behavior was strongly predictive of more depressive symptomatology and, unexpectedly, of better cognitive performance." https://journals.humankinetics.com/doi/pdf/10.1123/japa.13.3.294 https://journals.humankinetics.com/doi/pdf/10.1123/japa.13.3... >"Self-reported sedentary behavior was related to better performance on one cognitive task (trails A; p < .05)." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4861254/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4861254/ Obviously these are "undesirable" results, so you have to look a little bit deeper to find them.
    - nonbel 8y ago
      It looks like this was the study (emphasis added): Sedentary behavior associated with reduced medial temporal lobe thickness in middle-aged and older adults http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0195549 http://journals.plos.org/plosone/article?id=10.1371/journal....
      - MikkoFinell 8y ago
        As far as I know, thickness is a synonym for density. Quote from the article: To calculate thickness, for each gray matter voxel we computed the distance to the closest non-gray matter voxel. In 2D-space, for each voxel, we took the maximum distance value of the corresponding 3D voxels across all layers and multiplied by two. Mean thickness in each subregion was calculated by averaging thickness of all 2D voxels within each region of interest.
        nonbel 8y ago
        I think it is literal thickness since they report the results in units of millimeters. (eg figure 2)
        MikkoFinell 8y ago
        The authors explained quite carefully what they mean by thickness, as per the quote I provided. They are measuring the average distance between voxels in MRI scans. Since thickness is a measure of average distance in this case, it makes sense to provide it in millimeters like in the figure you mentioned. If you read the article, the authors make distinction between volume, surface area, and thickness under the "Discussion" part [0]. [0] http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0195549#sec010 http://journals.plos.org/plosone/article?id=10.1371/journal....
        nonbel 8y ago
        Their description sounds like literal thickness. They took the distance to the border (white matter) of all the points in a region. This is like the radius of a circle, and then multiplied by 2, to get a value like the diameter of a circle. It does sound like quite a convoluted process but I don't see where you are getting anything like "density" from that description. Also, reading the methods closer makes me think these are cherry picked results: >"Once segmentation is complete, the original images are interpolated by a factor of 7, resulting in a final voxel size of 0.39 × 0.39 × 0.43 mm. Next, up to 18 connected layers of gray matter are grown out from the boundary of white matter, using a region-expansion algorithm to cover all pixels defined as gray matter." Why 7? Why 18? These magic numbers shouldn't be there without some kind of sensitivity analysis. Finally, you can see the dimensions of the voxels is something determined by their methods, not a property of the brains.

Perhaps people who are either predisposed toward unhealthy outcomes, or are currently experiencing them (whether they realize it or not) are more sedentary. Correlation does not establish causation.

callesgg 8y ago

Um yes, the title should be more like: "Sitting correlates to Thinning in certain brain regions"

nonbel 8y ago
Is it bad to have a "thin" brain and good to have a "fat" brain now? Can't this brain region become too large? What if the area is enlarged due to inflammation/swelling and these people with "thinning" are those without that problem? If the brain is too large it is considered a problem: https://en.wikipedia.org/wiki/Megalencephaly https://en.wikipedia.org/wiki/Megalencephaly This guy apparently has the second largest brain ever measured, and he was a serial killer: https://en.wikipedia.org/wiki/Edward_H._Rulloff https://en.wikipedia.org/wiki/Edward_H._Rulloff
- MikkoFinell 8y ago
  The study was regarding density, not size.
  - nonbel 8y ago
    Where are you seeing that? Also, fine density/volume/mass, does it really change the argument? There is some optimal size for this region when it comes to certain functions, probably relative to the size of other regions. That size is probably suboptimal when it comes to other functions and there are tradeoffs going on. The press release seems to be assuming that thinner is bad automatically.
    - MikkoFinell 8y ago
      Yeah I do believe it makes a difference, because brain atrophy is linked to a range of cognitive impairments, for example strongly correlated with Alzheimer's disease. But you're right on the last point though, about assuming thinner is bad automatically. Heavy and chronic cannabis usage has been linked to an increase in density, but a reduction in total volume, which resulted in a slight overall decrease in IQ. The takeaway from all this being: Cognitive function is affected by a variety of parameters and we got more neuroscience to do still.
      - nonbel 8y ago
        >"Heavy and chronic cannabis usage has been linked to an increase in density, but a reduction in total volume, which resulted in a slight overall decrease in IQ." I wouldn't put much stock into these type of non-quantitative explanations wherein "this makes that go up which makes this go down", etc. Usually the researchers measure a bunch of different things, analyze the data in a bunch of different ways, and only publish whatever is "significant". This works at the single lab level and multi-lab level since the "non-significant" results are considered boring and don't get published. By "usually" I mean this is standard behavior. You can call it p-hacking, file drawer effect, and more recently "forking paths": http://andrewgelman.com/2017/12/29/forking-paths-plus-lack-theory-no-reason-believe/ http://andrewgelman.com/2017/12/29/forking-paths-plus-lack-t... >"Cognitive function is affected by a variety of parameters and we got more neuroscience to do still." Sure, that was the case before these studies were done too though.
    - always_good 8y ago
      > The press release seems to be assuming that thinner is bad automatically. Well, it's not unreasonable. I don't know of any literature that says that a sedentary lifestyle is healthy for the brain, but a lot of it has found the opposite. I would like to avoid anything that reproduces the neurological effects of being sedentary.
      - nonbel 8y ago
        >"I don't know of any literature that says that a sedentary lifestyle is healthy for the brain" Here are two I found: >"More sedentary behavior was strongly predictive of more depressive symptomatology and, unexpectedly, of better cognitive performance." https://journals.humankinetics.com/doi/pdf/10.1123/japa.13.3.294 https://journals.humankinetics.com/doi/pdf/10.1123/japa.13.3... >"Self-reported sedentary behavior was related to better performance on one cognitive task (trails A; p < .05)." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4861254/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4861254/ Obviously these are "undesirable" results, so you have to look a little bit deeper to find them.
  - nonbel 8y ago
    It looks like this was the study (emphasis added): Sedentary behavior associated with reduced medial temporal lobe thickness in middle-aged and older adults http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0195549 http://journals.plos.org/plosone/article?id=10.1371/journal....
    - MikkoFinell 8y ago
      As far as I know, thickness is a synonym for density. Quote from the article: To calculate thickness, for each gray matter voxel we computed the distance to the closest non-gray matter voxel. In 2D-space, for each voxel, we took the maximum distance value of the corresponding 3D voxels across all layers and multiplied by two. Mean thickness in each subregion was calculated by averaging thickness of all 2D voxels within each region of interest.
      - nonbel 8y ago
        I think it is literal thickness since they report the results in units of millimeters. (eg figure 2)
        MikkoFinell 8y ago
        The authors explained quite carefully what they mean by thickness, as per the quote I provided. They are measuring the average distance between voxels in MRI scans. Since thickness is a measure of average distance in this case, it makes sense to provide it in millimeters like in the figure you mentioned. If you read the article, the authors make distinction between volume, surface area, and thickness under the "Discussion" part [0]. [0] http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0195549#sec010 http://journals.plos.org/plosone/article?id=10.1371/journal....
        nonbel 8y ago
        Their description sounds like literal thickness. They took the distance to the border (white matter) of all the points in a region. This is like the radius of a circle, and then multiplied by 2, to get a value like the diameter of a circle. It does sound like quite a convoluted process but I don't see where you are getting anything like "density" from that description. Also, reading the methods closer makes me think these are cherry picked results: >"Once segmentation is complete, the original images are interpolated by a factor of 7, resulting in a final voxel size of 0.39 × 0.39 × 0.43 mm. Next, up to 18 connected layers of gray matter are grown out from the boundary of white matter, using a region-expansion algorithm to cover all pixels defined as gray matter." Why 7? Why 18? These magic numbers shouldn't be there without some kind of sensitivity analysis. Finally, you can see the dimensions of the voxels is something determined by their methods, not a property of the brains.