
Brain connectivity levels are equal in all mammals, including humans: study - hhs
https://www.aftau.org/press-release---brain-connectivity---july-20-2020
======
tbenst
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/)

~~~
egocodedinsol
Surely there's something to learn here though. I haven't read the original
paper but a quantity that's preserved across brain scales is either an
artifact or a neat insight.

Your criticism reads like someone accusing economists of being outrageously
misleading when they don't sample individual households but measure macro
indicators. It's like saying Ramon y cajal was ridiculous because he couldn't
image the neuropil effectively. Or like saying early optogenetics experiments
were ridiculous because who knows if you're stimulating a neuron in a
realistic manner?

And in any case, it's true that synapses are comically small relative to voxel
size, but we also have some reasonable information about projection patterns
and synapse number from various tracer or rabies studies with which you are no
doubt familiar.

I haven't read the nature paper the press release is about and I'm not a huge
fan of many d/fMRI practices or derived claims. And I've worked with enough
mammalian dwi data to be skeptical of specific connection claims. But this
strikes me as a rather interesting result even if you can't measure all the
synapses at the right resolution: either the tractography method has
connectivity conservation artifacts baked in, or there's something interesting
going on.

~~~
westurner
"fNIRS Compared with other neuroimaging techniques"
[https://en.wikipedia.org/wiki/Functional_near-
infrared_spect...](https://en.wikipedia.org/wiki/Functional_near-
infrared_spectroscopy#fNIRS_Compared_with_other_neuroimaging_techniques)

> _When comparing and contrasting these devices it is important to look at the
> temporal resolution, spatial resolution, and the degree of immobility._

~~~
egocodedinsol
I think I missed your overall point?

~~~
westurner
OP suggests that the spatial resolution of existing MRI neuroimaging
capabilities is insufficient to observe or so characterize or so generalize
about neuronal activity in mammalian species. fNIRS (functional near-infrared
spectroscopy) is one alternative neuroimaging capability that we could compare
fMRI with according to the criteria for comparison suggested in the cited
Wikipedia article: _" temporal resolution, spatial resolution, and the degree
of immobility"_.

------
jonnycomputer
"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
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)

~~~
wwwwewwww
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.

------
jjclarkson
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
It would be great/dystopian to, in the future, figure out what particular
people are good at by analysing their brains.

~~~
user982
A more accurate ASVAB?

~~~
toomuchtodo
I smell a DoD grant in the making!

------
gerbal
The full text of the paper is available on ResearchGate[1] or paywalled from
the publisher [2]

[1]
[https://www.researchgate.net/publication/342022024_Conservat...](https://www.researchgate.net/publication/342022024_Conservation_of_brain_connectivity_and_wiring_across_the_mammalian_class)

[2]
[https://www.nature.com/articles/s41593-020-0641-7](https://www.nature.com/articles/s41593-020-0641-7)

------
yboris
"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
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"

------
seesawtron
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/dagr...](https://drops.dagstuhl.de/opus/volltexte/2019/10358/pdf/dagrep_v008_i011_p112_18481.pdf)

------
ben_w
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?

~~~
elektropionir
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
Neat! So it's like an EM Flux measurement, but for the brain?! If so, that's
fascinating :-)

~~~
tbenst
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.

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jjclarkson
TAU is doing some interesting research: [https://www.aftau.org/press-release
---vapor](https://www.aftau.org/press-release---vapor)

