Why is the cerebral cortex folded?

[Lumpy]

@Blue_Blistering_Barnacle

but either technical challenges or inherent limitations to the design prevent us from “taking it further”.

This Scientific American article speculates that human brains are about as large and complex as biological limits will allow, short of inherently more efficient biochemistry:

http://www.cs.virginia.edu/~robins/The_Limits_of_Intelligence.pdf

[Der_Trihs]

@Chronos

But the brain isn’t “foreign” in the same way that sperm are: Sperm, being haploid, have a different genome than other bodily cells, but the brain should have the same genome. If autoimmune disorders of the brain are more common than elsewhere in the body, I would expect that to be an effect, not a cause, of the brain-blood barrier.

I recall reading of a hypothesis that the problem is that some parts of the immune system read the natural changes caused by learning in the neurons of the brain & spine as “damage”, and so will try to fix/destroy the cells if they can reach them. Therefore our ancestors evolved the blood/brain barrier to protect the brain.

[Leo_Bloom]

Interesting good thread.

This certainly comes out of nowhere:

@Corporal_Clegg

Long-held belief is that the brain is static. It has been scientifically established that the opposite is true–it dynamically grows new neurology and in ways that answer challenges we place upon ourselves or that come at us regularly. The cultural hang-over of “beliefs” related to the static brain are still ingrained in our elites who casually write off vast wealths of human potential and sentence individuals to be stigmatized when it’s not a matter of intelligence but readiness at a particular time. This also calls into question the general assumption that you can regimen education into a smorgasbord of studies. That model places the cart of learning before the cart of motivation and the ability to establish meaning relevance. The brain’s grows new neurology daily. But it’s mass does not change much. Evidence has been found that mass increases in some spots based upon what what does and pushes folds to accommodate that growth. The significance of neuroplacticity is monumental, but it is taken by an arrogant society as just some reaction that goes into effect only to repair loss of brain tissue through trauma et al. It must become the central criterion of radical reform and I’m sure that will take a great work to lead people to rebel against orthodoxy.

And goes back there too.

[MichaelEmouse]

@Ignotus

Still, the closest thing to brains we have engineered, i.e. integrated circuits, are also basically two-dimensional.

@leahcim

Which is also a manufacturing constraint. Certainly multi-layer, or fully three-dimensional ICs are conceived of. But they are hard to impossible to make with current tech.

I thought the main reason for the widespread use of 2D IC over 3D IC was heat dissipation, no?

Also, while consumer-level die-to-die 3D integration is recent*, isn’t the die itself a 3D integrated circuit with its several layers of interconnects? https://upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Cmos-chip_structure_in_2000s_(en).svg/2000px-Cmos-chip_structure_in_2000s_(en).svg.png

Do neurons only act like switches and amplifiers like transistors do? Do they form groups which resemble logic gates?

*RAM is an IC. Linking up several VRAM dies together as in HBM is 3D IC even if the link from VRAM to processors is 2.5D.

[KarlGrenze]

I’ll point out that several mammalian species have naturally smooth brains (lyssencephalia). These includes rodents, rabbits, and marsupials.

The cortical layers are a feature of the mammalian brain, but that is different from gyri and sulci (the grooves).

[Siam_Sam]

I recall reading that the Homo brain could not grow any larger and still be accommodated by natural birth. The baby’s head simply would simply no longer be able to fit through Mama’s opening. So the folds were evolution’s way of increasing brain size while keeping it in the same space. (I suppose birth canals could also increase, but there’s got to be a limit.)

On a side note, I’ve always been tickled by the Thai government’s push for what they call “brain-based learning.” I dunno, maybe it’s a real thing everywhere these days and I’ve only heard of it while here, but I’ve always wondered about the alternatives. Spleen-based learning? Liver-based learning?

[Leo_Bloom]

On the growth and form of cortical convolutions
http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3632.html

Tuomas Tallinen, Jun Young Chung, François Rousseau, Nadine Girard, Julien Lefèvre & L. Mahadevan
AffiliationsContributionsCorresponding authors
Nature Physics (2016) doi:10.1038/nphys3632
Received 27 September 2015 Accepted 09 December 2015 Published online 01 February 2016
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The rapid growth of the human cortex during development is accompanied by the folding of the brain into a highly convoluted structure1, 2, 3. Recent studies have focused on the genetic and cellular regulation of cortical growth4, 5, 6, 7, 8, but understanding the formation of the gyral and sulcal convolutions also requires consideration of the geometry and physical shaping of the growing brain9, 10, 11, 12, 13, 14, 15. To study this, we use magnetic resonance images to build a 3D-printed layered gel mimic of the developing smooth fetal brain; when immersed in a solvent, the outer layer swells relative to the core, mimicking cortical growth. This relative growth puts the outer layer into mechanical compression and leads to sulci and gyri similar to those in fetal brains. Starting with the same initial geometry, we also build numerical simulations of the brain modelled as a soft tissue with a growing cortex, and show that this also produces the characteristic patterns of convolutions over a realistic developmental course. All together, our results show that although many molecular determinants control the tangential expansion of the cortex, the size, shape, placement and orientation of the folds arise through iterations and variations of an elementary mechanical instability modulated by early fetal brain geometry.

Last week out of Stanford came the short vid Unfolding the Brain, also on the dynamics of the outside-in and inside-out models. (Unfolding The Brain - YouTube) It mentions translational medicine, somehow, of applying compression to (prevent?) aspects of autism.

Also: Wiki Gyrification

Gyrification

first graf:
Gyrification is the process of forming the characteristic folds of the cerebral cortex.[1] The peak of such a fold is called a gyrus (plural: gyri), and its trough is called a sulcus (plural: sulci). In most mammals, gyrification usually begins during embryogenesis and fetal development when neurogenesis is building the neuronal cortical layers, although some mammals, such as the ferret, are precociously born[citation needed] and develop gyri mainly after birth. Most rodents do not form cortical gyri. Primates, carnivores, cetaceans, and ungulates have extensive cortical gyri, with a few species exceptions, and gyrification in these animals continues well into postnatal life. Gyrification permits a larger cortical surface area and hence greater cognitive function in a smaller cranium.

[BigT]

@Siam_Sam

On a side note, I’ve always been tickled by the Thai government’s push for what they call “brain-based learning.” I dunno, maybe it’s a real thing everywhere these days and I’ve only heard of it while here, but I’ve always wondered about the alternatives. Spleen-based learning? Liver-based learning?

This is what Google gave me. Apparently it means teaching techniques based on cognitive science.