7 ms·

Brain connectivity levels are equal in all mammals, including humans: study

197 points by hhs 6y ago

ben_w 6y ago
I’m surprised that an MRI scan can allow a synapse-level reconstruction. So surprised that I suspect I’ve misunderstood (I can’t read the original paper — I probably wouldn’t understand it even if it wasn’t paywalled). Is MRI really that high-resolution now?
- jonnycomputer 6y ago
  No, it isn't that high resolution. I'd have to read paper to know what they mean.
- elektropionir 6y ago
  They did diffusion tensor imaging. What this does, using MRI, is determine the local anisotropy of water flow in each voxel. You assume that this anisotropy aligns with with the axis of axons, since they limit the diffusion of water across their axis (water diffuses along them). You can then use the principal directions of the diffusion tensor to estimate in what direction the water, i.e. the axons are "flowing" giving you an approximate picture of how axons connect different parts of the brain.
  - caust1c 6y ago
    Neat! So it's like an EM Flux measurement, but for the brain?! If so, that's fascinating :-)
    - tbenst 6y ago
      MRI is ~5 orders of magnitude less precise than EM. Not even close to cellular resolution, let along single axon resolution. You can only see axon tracts, where thousands of axons may make up one pixel.
  - leemailll 6y ago
    The problem is the voxels is not the same for each species considering brain size, and the limit of machine’s resolution.
- cmehdy 6y ago
  It's a bit of a tough read for outsiders (which I am), but with some basic understanding of the brain and a few lookups I think the paper is actually pretty readable in the end, so I'm attempting a quick explanation. There's a lot of interesting stuff to read about Connectomes[0] on wikipedia if you're curious about the mapping thing. I don't think they have an actual network map there, but in the initial pages of the paper they describe using MRI measurements to assess 200 areas they split the brain into ("normalized to 200 voxels per brain"), and they test their MRI methods by re-creating two tangentially related measurements which attach importance to geometric constraints of the brain. They mention: "Note that, as tractography does not actually measure axons but rather axonal bundles and fascicles, our length estimate reflects the wiring length of the macro-scale network." So it's more akin to getting a mapping of Earths (as in, each animal is one) and splitting it into 200 voxels, then looking at the density of fiber optic cables laid out, for many types of "Earths". So they don't see each strand but the bundles, which could mean that they don't know how much "data" actually goes through but they do know what bundles go where, which is more the point of connectivity. Then they go on to notice that there's overall little change of density across the measurements (40% maximum over 4 orders of magnitude of volumes) even though there are different structures (some might have only one one dominating continent while others have two, for example), and that within each "family" of measurements there's consistency in measured density across their samples. They also mention: "Results suggest that intra-hemispheric connectivity compensates for poorer inter-hemispheric connectivity, maintaining the overall connectivity." Which I think is something that at least from a functional standpoint has started to be looked at for humans (in studies like this[1]) but I don't know if any other study has done such an analysis as systematically as these guys, and I don't think ANY other study has done so across so many species and orders of magnitude of brain volumes. (I am happy to be corrected by any actually-knowledgeable person passing by, if they are so kind as to strike down any mistake) [0] https://en.wikipedia.org/wiki/Connectome https://en.wikipedia.org/wiki/Connectome [1] https://www.sciencedaily.com/releases/2019/11/191120070710.htm https://www.sciencedaily.com/releases/2019/11/191120070710.h...
- leemailll 6y ago
  MRI can’t do imaging at synapse level, even high powered on small animals. This has nothing to do with connectivity between neurons. It is more like they do correlations on correlations, and find mammals share some basic connection pattern (by correlation measurements). It might surprise those who don’t believe in evolution
- seesawtron 6y ago
  Of course not. This is a misleading title.
jonnycomputer 6y ago
"Our study revealed a universal law: Conservation of Brain Connectivity," Prof. Assaf concludes. "This law denotes that the efficiency of information transfer in the brain's neural network is equal in all mammals, including humans." I thought this was a little over the top. Its nothing like, say, the laws of gravitation. Its a regularity observed between species in a specific taxon on a specific planet at a specific time. And it was just one study. Still, I think the research is really cool. And I wonder whether this is an emergent property of how mammalian brains develop, or whether the regularity is the result of evolutionary pressure (because, i.e. there is selection for a specific connectivity profile).
- opwieurposiu 6y ago
  If someone gets split brain surgery, does this law mean they stop being a mammal? Personally I think you should get your nipples removed if you want to stop being a mammal. https://en.wikipedia.org/wiki/Split-brain https://en.wikipedia.org/wiki/Split-brain
  - darkerside 6y ago
    You do stop having a typical mammalian brain. This seems no more subjective than Moore's Law, for one, or Conway's Law for another.
  - draw_down 6y ago
    Humans typically have two arms, if one of yours gets chopped off you don't stop being human
  - tgb 6y ago
    It's a good question, but the article claims there's a compensation: "when connectivity between the hemispheres is high, connectivity within each hemisphere is relatively low, and vice versa". There's no reason that couldn't apply to someone with a split brain or a single hemisphere, at least after given time to adapt to the surgery.
  - wwwwewwww 6y ago
    Marsupials and monotremes lack the corpus callosum that facilities communication between left and right brain in placental mammal, so it is as if they already had this surgery. https://en.wikipedia.org/wiki/Corpus_callosum https://en.wikipedia.org/wiki/Corpus_callosum This seems to put into question their statement about "all mammals", but I haven't read the article, so maybe they actually mean placental mammals only. Monotreme mammals don't have nipples.
yboris 6y ago
"We discovered that brain connectivity — namely the efficiency of information transfer through the neural network — does not depend on either the size or structure of any specific brain. In other words, the brains of all mammals, from tiny mice through humans to large bulls and dolphins, exhibit equal connectivity, and information travels with the same efficiency within them."
- CiTyBear 6y ago
  I find this quote as important as yours: "This mechanism ensures that high connectivity in a specific area of the brain, possibly manifested through some special talent (e.g. sports or music) is always countered by relatively low connectivity in another part of the brain"
jjclarkson 6y ago
I found this interesting: "Our study revealed a universal law: Conservation of Brain Connectivity," Prof. Assaf concludes. "This law denotes that the efficiency of information transfer in the brain's neural network is equal in all mammals, including humans. We also discovered a compensation mechanism which balances the connectivity in every mammalian brain. This mechanism ensures that high connectivity in a specific area of the brain, possibly manifested through some special talent (e.g. sports or music) is always countered by relatively low connectivity in another part of the brain. In future projects we will investigate how the brain compensates for the enhanced connectivity associated with specific capabilities and learning processes."
- Tade0 6y ago
  It would be great/dystopian to, in the future, figure out what particular people are good at by analysing their brains.
  - deleted 6y ago
    [deleted]
  - msp_yc 6y ago
    Mr. Burns : Absolutely! Who could forget such a monstrous visage? She has the sloping brow and cranial bumpage of the career criminal. Waylon Smithers : Uh, Sir? Phrenology was dismissed as quackery 160 years ago. Mr. Burns : Of course you'd say that... you have the brainpan of a stagecoach tilter!
  - user982 6y ago
    A more accurate ASVAB?
    - toomuchtodo 6y ago
      I smell a DoD grant in the making!
    - Tade0 6y ago
      Probably less, but with better UX.
gerbal 6y ago
The full text of the paper is available on ResearchGate[1] or paywalled from the publisher [2] [1] https://www.researchgate.net/publication/342022024_Conservation_of_brain_connectivity_and_wiring_across_the_mammalian_class https://www.researchgate.net/publication/342022024_Conservat... [2] https://www.nature.com/articles/s41593-020-0641-7 https://www.nature.com/articles/s41593-020-0641-7
jjclarkson 6y ago
TAU is doing some interesting research: https://www.aftau.org/press-release---vapor https://www.aftau.org/press-release---vapor
tbenst 6y ago
This is outrageously misleading. To make a claim about the number of synapses between neurons based on MRI data is completely unwarranted. Voxel size (single volumetric pixel) in MRI is approximately 1mm, while synapse size is way less than a micron. You need resolution per pixel on the order of 10s of nanometers to identify synapses. I wouldn’t be surprised if a dead salmon also has “equal” connectivity: https://www.wired.com/2009/09/fmrisalmon/ https://www.wired.com/2009/09/fmrisalmon/
- gspr 6y ago
  Cool your outrage: https://en.wikipedia.org/wiki/Connectome#At_multiple_scales https://en.wikipedia.org/wiki/Connectome#At_multiple_scales
  - deleted 6y ago
    [deleted]
  - tbenst 6y ago
    “In other words, information travels from one location to another through the same number of synapses.” —-Yaniv Assaf This statement is outrageous, and an example of how some scientists gain the ire of their colleagues by exaggerating their findings and misleading the press.
- leemailll 6y ago
  And when you put the brain size into consideration, the results for some mammals might not too far a way from a fuzzy mosaic while human’s like a 10 k pixels image
- nabla9 6y ago
  They study macro-scale connectomes.
  - mmastrac 6y ago
    Would it be fair to say that the conclusions were that "large scale processing blocks have similar connection complexity across mammals, regardless of brain size?" -- obviously including that the complexity and/or function of the regions may be wildly different.
seesawtron 6y ago
Talking about brain connectivity being equal in all mammals using MRI? This is a joke! The resolution of MRI is too big to map the connectivity at the level of single synapses. Only Electron Microscopes are known to achieve that resolution and so far mapping a mammalian brain with Electron Microscope is very much impossible because of several reasons [0] [0] https://drops.dagstuhl.de/opus/volltexte/2019/10358/pdf/dagrep_v008_i011_p112_18481.pdf https://drops.dagstuhl.de/opus/volltexte/2019/10358/pdf/dagr...

197 points by hhs 6y ago

I’m surprised that an MRI scan can allow a synapse-level reconstruction. So surprised that I suspect I’ve misunderstood (I can’t read the original paper — I probably wouldn’t understand it even if it wasn’t paywalled). Is MRI really that high-resolution now?

jonnycomputer 6y ago
No, it isn't that high resolution. I'd have to read paper to know what they mean.
elektropionir 6y ago
They did diffusion tensor imaging. What this does, using MRI, is determine the local anisotropy of water flow in each voxel. You assume that this anisotropy aligns with with the axis of axons, since they limit the diffusion of water across their axis (water diffuses along them). You can then use the principal directions of the diffusion tensor to estimate in what direction the water, i.e. the axons are "flowing" giving you an approximate picture of how axons connect different parts of the brain.
- caust1c 6y ago
  Neat! So it's like an EM Flux measurement, but for the brain?! If so, that's fascinating :-)
  - tbenst 6y ago
    MRI is ~5 orders of magnitude less precise than EM. Not even close to cellular resolution, let along single axon resolution. You can only see axon tracts, where thousands of axons may make up one pixel.
- leemailll 6y ago
  The problem is the voxels is not the same for each species considering brain size, and the limit of machine’s resolution.
cmehdy 6y ago
It's a bit of a tough read for outsiders (which I am), but with some basic understanding of the brain and a few lookups I think the paper is actually pretty readable in the end, so I'm attempting a quick explanation. There's a lot of interesting stuff to read about Connectomes[0] on wikipedia if you're curious about the mapping thing. I don't think they have an actual network map there, but in the initial pages of the paper they describe using MRI measurements to assess 200 areas they split the brain into ("normalized to 200 voxels per brain"), and they test their MRI methods by re-creating two tangentially related measurements which attach importance to geometric constraints of the brain. They mention: "Note that, as tractography does not actually measure axons but rather axonal bundles and fascicles, our length estimate reflects the wiring length of the macro-scale network." So it's more akin to getting a mapping of Earths (as in, each animal is one) and splitting it into 200 voxels, then looking at the density of fiber optic cables laid out, for many types of "Earths". So they don't see each strand but the bundles, which could mean that they don't know how much "data" actually goes through but they do know what bundles go where, which is more the point of connectivity. Then they go on to notice that there's overall little change of density across the measurements (40% maximum over 4 orders of magnitude of volumes) even though there are different structures (some might have only one one dominating continent while others have two, for example), and that within each "family" of measurements there's consistency in measured density across their samples. They also mention: "Results suggest that intra-hemispheric connectivity compensates for poorer inter-hemispheric connectivity, maintaining the overall connectivity." Which I think is something that at least from a functional standpoint has started to be looked at for humans (in studies like this[1]) but I don't know if any other study has done such an analysis as systematically as these guys, and I don't think ANY other study has done so across so many species and orders of magnitude of brain volumes. (I am happy to be corrected by any actually-knowledgeable person passing by, if they are so kind as to strike down any mistake) [0] https://en.wikipedia.org/wiki/Connectome https://en.wikipedia.org/wiki/Connectome [1] https://www.sciencedaily.com/releases/2019/11/191120070710.htm https://www.sciencedaily.com/releases/2019/11/191120070710.h...
leemailll 6y ago
MRI can’t do imaging at synapse level, even high powered on small animals. This has nothing to do with connectivity between neurons. It is more like they do correlations on correlations, and find mammals share some basic connection pattern (by correlation measurements). It might surprise those who don’t believe in evolution
seesawtron 6y ago
Of course not. This is a misleading title.

jonnycomputer 6y ago

"Our study revealed a universal law: Conservation of Brain Connectivity," Prof. Assaf concludes. "This law denotes that the efficiency of information transfer in the brain's neural network is equal in all mammals, including humans." I thought this was a little over the top. Its nothing like, say, the laws of gravitation. Its a regularity observed between species in a specific taxon on a specific planet at a specific time. And it was just one study. Still, I think the research is really cool. And I wonder whether this is an emergent property of how mammalian brains develop, or whether the regularity is the result of evolutionary pressure (because, i.e. there is selection for a specific connectivity profile).

opwieurposiu 6y ago
If someone gets split brain surgery, does this law mean they stop being a mammal? Personally I think you should get your nipples removed if you want to stop being a mammal. https://en.wikipedia.org/wiki/Split-brain https://en.wikipedia.org/wiki/Split-brain
- darkerside 6y ago
  You do stop having a typical mammalian brain. This seems no more subjective than Moore's Law, for one, or Conway's Law for another.
- draw_down 6y ago
  Humans typically have two arms, if one of yours gets chopped off you don't stop being human
- tgb 6y ago
  It's a good question, but the article claims there's a compensation: "when connectivity between the hemispheres is high, connectivity within each hemisphere is relatively low, and vice versa". There's no reason that couldn't apply to someone with a split brain or a single hemisphere, at least after given time to adapt to the surgery.
- wwwwewwww 6y ago
  Marsupials and monotremes lack the corpus callosum that facilities communication between left and right brain in placental mammal, so it is as if they already had this surgery. https://en.wikipedia.org/wiki/Corpus_callosum https://en.wikipedia.org/wiki/Corpus_callosum This seems to put into question their statement about "all mammals", but I haven't read the article, so maybe they actually mean placental mammals only. Monotreme mammals don't have nipples.

yboris 6y ago

"We discovered that brain connectivity — namely the efficiency of information transfer through the neural network — does not depend on either the size or structure of any specific brain. In other words, the brains of all mammals, from tiny mice through humans to large bulls and dolphins, exhibit equal connectivity, and information travels with the same efficiency within them."

CiTyBear 6y ago
I find this quote as important as yours: "This mechanism ensures that high connectivity in a specific area of the brain, possibly manifested through some special talent (e.g. sports or music) is always countered by relatively low connectivity in another part of the brain"

jjclarkson 6y ago

I found this interesting: "Our study revealed a universal law: Conservation of Brain Connectivity," Prof. Assaf concludes. "This law denotes that the efficiency of information transfer in the brain's neural network is equal in all mammals, including humans. We also discovered a compensation mechanism which balances the connectivity in every mammalian brain. This mechanism ensures that high connectivity in a specific area of the brain, possibly manifested through some special talent (e.g. sports or music) is always countered by relatively low connectivity in another part of the brain. In future projects we will investigate how the brain compensates for the enhanced connectivity associated with specific capabilities and learning processes."

Tade0 6y ago
It would be great/dystopian to, in the future, figure out what particular people are good at by analysing their brains.
- deleted 6y ago
  [deleted]
- msp_yc 6y ago
  Mr. Burns : Absolutely! Who could forget such a monstrous visage? She has the sloping brow and cranial bumpage of the career criminal. Waylon Smithers : Uh, Sir? Phrenology was dismissed as quackery 160 years ago. Mr. Burns : Of course you'd say that... you have the brainpan of a stagecoach tilter!
- user982 6y ago
  A more accurate ASVAB?
  - toomuchtodo 6y ago
    I smell a DoD grant in the making!
  - Tade0 6y ago
    Probably less, but with better UX.

gerbal 6y ago

The full text of the paper is available on ResearchGate[1] or paywalled from the publisher [2] [1] https://www.researchgate.net/publication/342022024_Conservation_of_brain_connectivity_and_wiring_across_the_mammalian_class https://www.researchgate.net/publication/342022024_Conservat... [2] https://www.nature.com/articles/s41593-020-0641-7 https://www.nature.com/articles/s41593-020-0641-7

jjclarkson 6y ago

TAU is doing some interesting research: https://www.aftau.org/press-release---vapor https://www.aftau.org/press-release---vapor

tbenst 6y ago

This is outrageously misleading. To make a claim about the number of synapses between neurons based on MRI data is completely unwarranted. Voxel size (single volumetric pixel) in MRI is approximately 1mm, while synapse size is way less than a micron. You need resolution per pixel on the order of 10s of nanometers to identify synapses. I wouldn’t be surprised if a dead salmon also has “equal” connectivity: https://www.wired.com/2009/09/fmrisalmon/ https://www.wired.com/2009/09/fmrisalmon/

gspr 6y ago
Cool your outrage: https://en.wikipedia.org/wiki/Connectome#At_multiple_scales https://en.wikipedia.org/wiki/Connectome#At_multiple_scales
- deleted 6y ago
  [deleted]
- tbenst 6y ago
  “In other words, information travels from one location to another through the same number of synapses.” —-Yaniv Assaf This statement is outrageous, and an example of how some scientists gain the ire of their colleagues by exaggerating their findings and misleading the press.
leemailll 6y ago
And when you put the brain size into consideration, the results for some mammals might not too far a way from a fuzzy mosaic while human’s like a 10 k pixels image
nabla9 6y ago
They study macro-scale connectomes.
- mmastrac 6y ago
  Would it be fair to say that the conclusions were that "large scale processing blocks have similar connection complexity across mammals, regardless of brain size?" -- obviously including that the complexity and/or function of the regions may be wildly different.

seesawtron 6y ago

Talking about brain connectivity being equal in all mammals using MRI? This is a joke! The resolution of MRI is too big to map the connectivity at the level of single synapses. Only Electron Microscopes are known to achieve that resolution and so far mapping a mammalian brain with Electron Microscope is very much impossible because of several reasons [0] [0] https://drops.dagstuhl.de/opus/volltexte/2019/10358/pdf/dagrep_v008_i011_p112_18481.pdf https://drops.dagstuhl.de/opus/volltexte/2019/10358/pdf/dagr...