6 ms·

I do MRI work, and my gut is that none of the claims about dance vs. exercise would replicate. The behavioral data suggests that activity of some type will impr

by bogtog 2y ago

I do MRI work, and my gut is that none of the claims about dance vs. exercise would replicate. The behavioral data suggests that activity of some type will improve cognitive function (main effects of time). Such beneficial effects of activity on the brain have been shown before, and this is generally accepted. However, the authors' behavioral data doesn't show any difference between the dance vs. exercise groups. This means that the study is overall off to a pretty bad start if their goal is to study dance vs. exercise differences... The brain data claims to show that the dance vs. exercise groups showed different levels of improvement in various regions. However, the brain effects are tiny and are probably just random noise (I'm referring to those red spots, which are very small and almost certainly don't reflect proper correction for multiple hypotheses given that the authors effectively tested 1000s or 10000s of different areas). The authors' claims about BDNF are supported by a p-value of p = .046, and having main conclusions hinge on p-values of p > .01 usually means the conclusions are rubbish. In general, my priors on "we can detect subtle changes in brain matter over a 6-week period" are also very low. Perhaps, a study with this sample size could show that activity of some kind influences the brain over such a short length, but I am extremely skeptical that this type of study could detect differences between dance vs. exercise effects.

aswegs8 2y ago
I lack the in-depth knowledge but correcting p-value thresholds for multiple hypotheses is very basic science. I doubt your criticism is valid given that some basic error like this would never pass peer review.
- bogtog 2y ago
  Correcting for p-values in brain imaging research is kinda elaborate, since you are essentially performing a t-test separately for each brain voxel. A brain image like the authors' will have about a million voxels (0.7 x 0.7 x 0.7 mm voxels). For multiple hypothesis correction, correcting for 1 million tests would be overly strict because neighboring voxels are highly correlated with one another, and it's unlikely for brain effects to really be confined to such a small area. Hence, researchers usually define a primary threshold for voxels (here p < .001 uncorrected), and then look for patches of many p < .001 voxels together. Here, the authors stated that they looked for patches of at least 50 contiguous voxels. The authors are just using some loose old-timey heuristic without justification or citation. These have been getting phased out mostly in the past decade. These types of heuristics don't actually test to establish that these thresholds won't yield tons of false positives (one of the best ways to do this is to basically randomly shuffle your data and see what are the actual cluster sizes generated by chance). > some basic error like this would never pass peer review It indeed shouldn't pass peer review! Yet, here we are. I think standards have gotten better since the paper's publication (2018), but there are no doubt there are still many reviewers who don't have a good intuition about what a significant cluster size should be. Off the top of my head, I can't give an exact number on the cluster size needed, but I'd be willing to bet a ton that what the authors used is not enough.
- deleted 2y ago
  [deleted]
bbstats 2y ago
I think all the things that dance brings to the table over the mean "exercise" are clear first-principles wins (using your whole body, listening and dancing in rhythm, listening to music, letting yourself go / being silly)
zophiana 2y ago
I agree that the sample size might be a bit small so it could be noise, but the study did went 6-month not 6-weeks. And there are findings like these https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0196636#pone-0196636-g004 https://journals.plos.org/plosone/article?id=10.1371/journal...
- bogtog 2y ago
  Thanks, that sounds more reasonable. I'm still generally bearish on this type of brain-volume-change work (and extremely so on any study trying to compare brain-volume effects between different groups), but I guess 6-months is a finer premise.
- wdkrnls 2y ago
  Or it could be a problem of seeking statistical detection of any difference whatsoever versus detecting a practically meaningful difference... a type III error (answering the wrong question).
westurner 2y ago
Cardiovascular exercise correlates with subsequent synthesis of endocannabinoids, which affect hippocampal neurogeneration and probably thereby neuroplasticity. From "Environment shapes emotional cognitive abilities more than genes" (2024) https://news.ycombinator.com/item?id=40105068#40107602 https://news.ycombinator.com/item?id=40105068#40107602 : > hippocampal plasticity and hippocampal neurogenesis also appear to be affected by dancing and omega-3,6 (which are transformed into endocannabinoids by the body): https://news.ycombinator.com/item?id=15109698 https://news.ycombinator.com/item?id=15109698 Also, isn't there selection bias to observational dance studies? If not in good general health, is a person likely to pursue regular dancing? Though, dance lifts mood and gets the cardiovascular system going. Dance involves spatial sense and proprioception and probably all of the senses.
agumonkey 2y ago
My random opinion is that dance or dance like activities are a sweet spot between low intensity and high intensity exercise that involves a lot more balance, coordination and fluidity than most physical activities promoted for health overall (they're either too simple or too hard), these traits are (I believe) very important to your brain. Add the social aspect as an important bonus.
- pjerem 2y ago
  Totally anecdotal and probably 99% placebo but I started rollerblading (which also require _a lot_ of balance and coordination) for the first time in my life, like, I take courses in a skatepark and never wore rollerblades before (I’m 33). After some weeks I’m totally perceiving "something" changed in my brain. It’s like doing mental things is somehow easier. I also happen to microdose since a few months ago but the change I felt coincided exactly about when I felt my fear to fall disappeared, when I "got" the balancing. That’s totally an anecdote and not science but this feeling of change in my brain was so strong that I perceived it.
  - agumonkey 2y ago
    I'd put all our stories in the same bag as taxi drivers having brain areas very deeply developed. I'm not surprised by your story. After health issues, my brain was clogged most of the time, and anything involving balance, rotation, rapidly moving surroundings. I tried a lot of stuff to feel my brain working again, one of the most impactful was balancing on a wood beam and trying to pivot (not far from roller skates moves). Our brain respond very well to some primitive stimuli (visual, balance, geometry).
- WalterBright 2y ago
  Yes, moving as one with your partner is a big part of it, and where much of the pleasure comes from.
  - agumonkey 2y ago
    Yeah I believe that our brains are extremely sensitive to shared experience, work, art, movement or else (singing in harmony would work too). It might even tap in primitive toddler brain phases.
0xcde4c3db 2y ago
> The authors' claims about BDNF are supported by a p-value of p = .046, and having main conclusions hinge on p-values of p > .01 usually means the conclusions are rubbish. Also, I don't have the references handy, but I recall other studies showing that exercise-induced BDNF changes can be mediated by e.g. air pollution. So even if the difference there is real, it might be premature to attribute it specifically to the mode of training.
- tech_ken 2y ago
  This is a good point, maybe the dance studio has a better air filtration system than the other exercise location
givemeethekeys 2y ago
Do more complex movements stimulate our neural pathways more than less complex movements?
tech_ken 2y ago
> The authors' claims about BDNF are supported by a p-value of p = .046, and having main conclusions hinge on p-values of p > .01 usually means the conclusions are rubbish. Your other points I agree with but I actually think the BDNF result has some standing. I'm looking at Fig. 4 and just by an eyeball test there's clear difference in the distributions of the intra-individual BDNF increase. It's not like there's some miniscule variation in the means that they make significant with really small error bars, the actual effect size appears to be notable. Moreover there's clearly some effect on the width of the distributions which could support their ultimate conclusion (ex. even if the mean effect is the same, it's possible the population-wide ceiling on gains is higher for dance). Now with all that said this could definitely still be a multiple comparisons thing, I'm just a statistician with no background in neuro-stuff so possibly the BDNF thing is just a bad indicator here. Certainly the behavioral outcomes not showing an interaction difference isn't a great sign as you point out, but in my personal and unimportant opinion I would at least say this study would be good justification for a follow-up with a better design and bigger population.
- bogtog 2y ago
  I know nearly nothing about BDNF specifically. Whether it should motivate a follow-up is mostly only something known to the authors, as a p = .046 suggests a chance they may have tested numerous outcome variables and reported only one (e.g,. this could very well be 1/10). The fact that the p-value is almost comically close to p = .05, makes me suspect that this happened. Perhaps, if this goes in line with other BDNF research, then that could motivate it some further work. Notably, even if we take this p = .046 as a given, and assume there was no p-hacking, then this type of result implies that statistical power is tiny, and a proper "bigger population" study would likely have to be several hundreds of people. Even a study with 50% power, should have a majority of significant results land p < .01.
  - tech_ken 2y ago
    > assume there was no p-hacking Agree that this is definitely an assumption one needs to make, could easily be that BDNF was one variable among many unreported ones, and this case would be consistent with the other outcome variables in the paper so seems plausible. > this type of result implies that statistical power is tiny, Yes, definitely, BUT the effect in question is an interaction effect so yeah, power's just going to be small from the nature of the design. I was definitely thinking that you'd be looking at a follow up study of the size of multiple hundreds to confirm something like this. I'm realizing that thinking this is a trivial follow-up is is the difference between someone actually might work on real experiments and someone who just works with the numbers. Just want to re-emphasize though that the thing which makes me give this result (some) credence (assuming it's not a desk drawer p-hack) is just the distributions of the observation variable for the two treatment groups. Like even if the means of the BDNF increase are equal between the two arms of the trial, and this p-value is a false pos (which as you say, seems very possible), there's still clearly some other differences between the groups. I strongly suspect a quantile regression on the p50 or p75, rather than an ANOVA on the means, would show a 'more significant' effect; heck even just a log-linear model or something seems like it would be an improvement since there's clearly some skew in the 'Dance' population.
jon_richards 2y ago
See also the dead salmon study https://www.scientificamerican.com/blog/scicurious-brain/ignobel-prize-in-neuroscience-the-dead-salmon-study/ https://www.scientificamerican.com/blog/scicurious-brain/ign...
- hunter-gatherer 2y ago
  > "The original poster almost didn't make it to a conference, but when it did, it made a major splash" Best pun ever.
starluz 2y ago
[flagged]
yellow_postit 2y ago
Replicability was my first thought as well. These papers make great headlines but how much shaky pyramids of conclusions are built on non-reproducible conclusions?
kukkeliskuu 2y ago
I have done lots of free-form couples dancing (over 20 years, several times per week, some of it in complex styles like argentine tango) and in my first-hand experience the major difference from other kinds of exercise is that you need to harmonize your movements with your partner and music, and you need to improvise. The complexity of the movement is not it, nor the "exercise". There is lots of other research suggesting that couples dancing is more beneficial to the mental health and memory than other kinds of exercise. That said (and having no background in an very little knowledge of MRI research), I am also skeptical like you that there would appear such clear visible signs so soon in the brain images.
- johtso 2y ago
  I also wonder if even just the close physical contact itself has a positive impact on brain chemistry.
  - kukkeliskuu 2y ago
    Yes, I think it does. But in my understanding that has been controlled in the research as well. Also, there is also a short-term downside to the physical contact. For me it took years of training to become less anxious about the proximity of another person. You are minutes at a time in hugging position with a person who can be a total stranger.
- Notatheist 2y ago
  I'm a professional dancer and music and freestyle are the most demanding aspects of dance by far. That said I'm also skeptical. Music and dance are being compared to "bicycle ergometers" and "training with equipment such as barbells and rubber bands". I'm pretty sure only one of these groups was having any fun. Unless the dance group were forced to social dance bachata in which case the misery probably evens out.
  - zemvpferreira 2y ago
    You might be surprised at how many people enjoy the feeling of grinding out improvement in the gym. In my experience it can be a lot more fun than dancing for certain personality types (mine included)

by bogtog 2y ago

aswegs8 2y ago

I lack the in-depth knowledge but correcting p-value thresholds for multiple hypotheses is very basic science. I doubt your criticism is valid given that some basic error like this would never pass peer review.

bogtog 2y ago
Correcting for p-values in brain imaging research is kinda elaborate, since you are essentially performing a t-test separately for each brain voxel. A brain image like the authors' will have about a million voxels (0.7 x 0.7 x 0.7 mm voxels). For multiple hypothesis correction, correcting for 1 million tests would be overly strict because neighboring voxels are highly correlated with one another, and it's unlikely for brain effects to really be confined to such a small area. Hence, researchers usually define a primary threshold for voxels (here p < .001 uncorrected), and then look for patches of many p < .001 voxels together. Here, the authors stated that they looked for patches of at least 50 contiguous voxels. The authors are just using some loose old-timey heuristic without justification or citation. These have been getting phased out mostly in the past decade. These types of heuristics don't actually test to establish that these thresholds won't yield tons of false positives (one of the best ways to do this is to basically randomly shuffle your data and see what are the actual cluster sizes generated by chance). > some basic error like this would never pass peer review It indeed shouldn't pass peer review! Yet, here we are. I think standards have gotten better since the paper's publication (2018), but there are no doubt there are still many reviewers who don't have a good intuition about what a significant cluster size should be. Off the top of my head, I can't give an exact number on the cluster size needed, but I'd be willing to bet a ton that what the authors used is not enough.
deleted 2y ago
[deleted]

bbstats 2y ago

I think all the things that dance brings to the table over the mean "exercise" are clear first-principles wins (using your whole body, listening and dancing in rhythm, listening to music, letting yourself go / being silly)

zophiana 2y ago

I agree that the sample size might be a bit small so it could be noise, but the study did went 6-month not 6-weeks. And there are findings like these https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0196636#pone-0196636-g004 https://journals.plos.org/plosone/article?id=10.1371/journal...

bogtog 2y ago
Thanks, that sounds more reasonable. I'm still generally bearish on this type of brain-volume-change work (and extremely so on any study trying to compare brain-volume effects between different groups), but I guess 6-months is a finer premise.
wdkrnls 2y ago
Or it could be a problem of seeking statistical detection of any difference whatsoever versus detecting a practically meaningful difference... a type III error (answering the wrong question).

westurner 2y ago

Cardiovascular exercise correlates with subsequent synthesis of endocannabinoids, which affect hippocampal neurogeneration and probably thereby neuroplasticity. From "Environment shapes emotional cognitive abilities more than genes" (2024) https://news.ycombinator.com/item?id=40105068#40107602 https://news.ycombinator.com/item?id=40105068#40107602 : > hippocampal plasticity and hippocampal neurogenesis also appear to be affected by dancing and omega-3,6 (which are transformed into endocannabinoids by the body): https://news.ycombinator.com/item?id=15109698 https://news.ycombinator.com/item?id=15109698 Also, isn't there selection bias to observational dance studies? If not in good general health, is a person likely to pursue regular dancing? Though, dance lifts mood and gets the cardiovascular system going. Dance involves spatial sense and proprioception and probably all of the senses.

agumonkey 2y ago

My random opinion is that dance or dance like activities are a sweet spot between low intensity and high intensity exercise that involves a lot more balance, coordination and fluidity than most physical activities promoted for health overall (they're either too simple or too hard), these traits are (I believe) very important to your brain. Add the social aspect as an important bonus.

pjerem 2y ago
Totally anecdotal and probably 99% placebo but I started rollerblading (which also require _a lot_ of balance and coordination) for the first time in my life, like, I take courses in a skatepark and never wore rollerblades before (I’m 33). After some weeks I’m totally perceiving "something" changed in my brain. It’s like doing mental things is somehow easier. I also happen to microdose since a few months ago but the change I felt coincided exactly about when I felt my fear to fall disappeared, when I "got" the balancing. That’s totally an anecdote and not science but this feeling of change in my brain was so strong that I perceived it.
- agumonkey 2y ago
  I'd put all our stories in the same bag as taxi drivers having brain areas very deeply developed. I'm not surprised by your story. After health issues, my brain was clogged most of the time, and anything involving balance, rotation, rapidly moving surroundings. I tried a lot of stuff to feel my brain working again, one of the most impactful was balancing on a wood beam and trying to pivot (not far from roller skates moves). Our brain respond very well to some primitive stimuli (visual, balance, geometry).
WalterBright 2y ago
Yes, moving as one with your partner is a big part of it, and where much of the pleasure comes from.
- agumonkey 2y ago
  Yeah I believe that our brains are extremely sensitive to shared experience, work, art, movement or else (singing in harmony would work too). It might even tap in primitive toddler brain phases.

0xcde4c3db 2y ago

> The authors' claims about BDNF are supported by a p-value of p = .046, and having main conclusions hinge on p-values of p > .01 usually means the conclusions are rubbish. Also, I don't have the references handy, but I recall other studies showing that exercise-induced BDNF changes can be mediated by e.g. air pollution. So even if the difference there is real, it might be premature to attribute it specifically to the mode of training.

tech_ken 2y ago
This is a good point, maybe the dance studio has a better air filtration system than the other exercise location

givemeethekeys 2y ago

Do more complex movements stimulate our neural pathways more than less complex movements?

tech_ken 2y ago

> The authors' claims about BDNF are supported by a p-value of p = .046, and having main conclusions hinge on p-values of p > .01 usually means the conclusions are rubbish. Your other points I agree with but I actually think the BDNF result has some standing. I'm looking at Fig. 4 and just by an eyeball test there's clear difference in the distributions of the intra-individual BDNF increase. It's not like there's some miniscule variation in the means that they make significant with really small error bars, the actual effect size appears to be notable. Moreover there's clearly some effect on the width of the distributions which could support their ultimate conclusion (ex. even if the mean effect is the same, it's possible the population-wide ceiling on gains is higher for dance). Now with all that said this could definitely still be a multiple comparisons thing, I'm just a statistician with no background in neuro-stuff so possibly the BDNF thing is just a bad indicator here. Certainly the behavioral outcomes not showing an interaction difference isn't a great sign as you point out, but in my personal and unimportant opinion I would at least say this study would be good justification for a follow-up with a better design and bigger population.

bogtog 2y ago
I know nearly nothing about BDNF specifically. Whether it should motivate a follow-up is mostly only something known to the authors, as a p = .046 suggests a chance they may have tested numerous outcome variables and reported only one (e.g,. this could very well be 1/10). The fact that the p-value is almost comically close to p = .05, makes me suspect that this happened. Perhaps, if this goes in line with other BDNF research, then that could motivate it some further work. Notably, even if we take this p = .046 as a given, and assume there was no p-hacking, then this type of result implies that statistical power is tiny, and a proper "bigger population" study would likely have to be several hundreds of people. Even a study with 50% power, should have a majority of significant results land p < .01.
- tech_ken 2y ago
  > assume there was no p-hacking Agree that this is definitely an assumption one needs to make, could easily be that BDNF was one variable among many unreported ones, and this case would be consistent with the other outcome variables in the paper so seems plausible. > this type of result implies that statistical power is tiny, Yes, definitely, BUT the effect in question is an interaction effect so yeah, power's just going to be small from the nature of the design. I was definitely thinking that you'd be looking at a follow up study of the size of multiple hundreds to confirm something like this. I'm realizing that thinking this is a trivial follow-up is is the difference between someone actually might work on real experiments and someone who just works with the numbers. Just want to re-emphasize though that the thing which makes me give this result (some) credence (assuming it's not a desk drawer p-hack) is just the distributions of the observation variable for the two treatment groups. Like even if the means of the BDNF increase are equal between the two arms of the trial, and this p-value is a false pos (which as you say, seems very possible), there's still clearly some other differences between the groups. I strongly suspect a quantile regression on the p50 or p75, rather than an ANOVA on the means, would show a 'more significant' effect; heck even just a log-linear model or something seems like it would be an improvement since there's clearly some skew in the 'Dance' population.

jon_richards 2y ago

See also the dead salmon study https://www.scientificamerican.com/blog/scicurious-brain/ignobel-prize-in-neuroscience-the-dead-salmon-study/ https://www.scientificamerican.com/blog/scicurious-brain/ign...

hunter-gatherer 2y ago
> "The original poster almost didn't make it to a conference, but when it did, it made a major splash" Best pun ever.

starluz 2y ago

[flagged]

yellow_postit 2y ago

Replicability was my first thought as well. These papers make great headlines but how much shaky pyramids of conclusions are built on non-reproducible conclusions?

kukkeliskuu 2y ago

I have done lots of free-form couples dancing (over 20 years, several times per week, some of it in complex styles like argentine tango) and in my first-hand experience the major difference from other kinds of exercise is that you need to harmonize your movements with your partner and music, and you need to improvise. The complexity of the movement is not it, nor the "exercise". There is lots of other research suggesting that couples dancing is more beneficial to the mental health and memory than other kinds of exercise. That said (and having no background in an very little knowledge of MRI research), I am also skeptical like you that there would appear such clear visible signs so soon in the brain images.

johtso 2y ago
I also wonder if even just the close physical contact itself has a positive impact on brain chemistry.
- kukkeliskuu 2y ago
  Yes, I think it does. But in my understanding that has been controlled in the research as well. Also, there is also a short-term downside to the physical contact. For me it took years of training to become less anxious about the proximity of another person. You are minutes at a time in hugging position with a person who can be a total stranger.
Notatheist 2y ago
I'm a professional dancer and music and freestyle are the most demanding aspects of dance by far. That said I'm also skeptical. Music and dance are being compared to "bicycle ergometers" and "training with equipment such as barbells and rubber bands". I'm pretty sure only one of these groups was having any fun. Unless the dance group were forced to social dance bachata in which case the misery probably evens out.
- zemvpferreira 2y ago
  You might be surprised at how many people enjoy the feeling of grinding out improvement in the gym. In my experience it can be a lot more fun than dancing for certain personality types (mine included)