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> Is the neocortex not an outer layer? That is not present in reptiles? So how is the stratified model incorrect as a high-level structural categorization? Not

by xg15 3y ago

> Is the neocortex not an outer layer? That is not present in reptiles? So how is the stratified model incorrect as a high-level structural categorization? Not sure about reptiles, but the author write this about mammals: > Neurobiologists do not debate whether any cortical regions are evolutionarily newer in some mammals than others. To be clear, even the prefrontal cortex, a region associated with reason and action planning, is not a uniquely human structure. Although there is debate concerning the relative size of the prefrontal cortex in humans compared with nonhuman animals (Passingham & Smaers, 2014; Sherwood, Bauernfeind, Bianchi, Raghanti, & Hof, 2012; Teffer & Semendeferi, 2012), all mammals have a prefrontal cortex. I also read some interesting papers a few years ago about corvids - particular New Caledonian Crows: Those animals do not have a neocortex and hence were thought incapable of many higher-level cognitive tasks, such as planning, tool use, etc. Turned out the crows were in fact capable of them. One hypothesis I read suggested that, as crow brains are structured differently, another structure may have taken the role that the neocortex has in humans. So even if it's an anatomical distinction, it's an unreliable indicator of mental capacity.

crazygringo 3y ago
OK, but again -- none of that refutes the triune brain hypothesis at all. Literally nobody is claiming that only humans have neocortexes. Nor is anyone claiming it's an indicator of mental capacity. The recent discoveries about crows were interesting, but that doesn't have anything to do with the fact that the neocortex in mammals plays a particular, functional, well-recognized role.
- theptip 3y ago
  The refutation is of the idea that it’s a strictly chronological layering, with the old layers inside and intact. The correct view is that while the neocortex is indeed mostly new, the “older” more central structures were modified throughout evolution.
  - JohnAaronNelson 3y ago
    No one thinks the older structures are static. No one is arguing that. It's a simplified model about the origin. This argument is akin to saying we're not "newer" apes ala > The refutation is of the idea that it’s a strictly chronological ordering of species, with the old species still inside and intact. The correct view is that while homosapiens are indeed mostly "newer", the “older” apes were also modified throughout evolution Obviously.
    - theptip 3y ago
      I mean… the quote from TFA that they are arguing against is > As Paul MacLean (1964), originator of the triune-brain theory, stated, >> man, it appears, has inherited essentially three brains. Frugal Nature in developing her paragon threw nothing away. The oldest of his brains is basically reptilian; the second has been inherited from lower mammals; and the third and newest brain is a late mammalian development which reaches a pinnacle in man and gives him his unique power of symbolic language. And they quote other textbooks that are making claims along these lines too; this is right at the beginning of TFA. So I think you are wrong that “no one thinks that”. Of course they don’t think the old brains are 100% static but there are claims that they are largely conserved.
      - tigen 3y ago
        MacLean doesn't say the brain is an onion with a tiny reptile inside!
      - jacquesm 3y ago
        > there are claims that they are largely conserved. That they're not static doesn't necessarily mean that they aren't largely conserved.
    - Retric 3y ago
      It’s an incorrect and misleading model about the origin. Bat wings and bird wings share many traits but the common answer didn’t fly it’s simply convergent evolution. The brain structures of that same common ancestor is only vaguely related to modern structures in mammals and reptiles. Modern reptiles, birds, and humans have experienced the same amount of evolution. There’s similar traits, but we don’t call whale flippers hands because that’s what the structures was in some of their ancestors or even what it is in related species. Similarly we don’t call human hands flippers because that’s what the structure started out as even further back and it’s still preforming that function in modern fish. The human visual cortex is larger than most creatures entire brain, it’s a wildly different structure than you find on a frog which plays a wider role in cognition than just decoding vision.
- makeitdouble 3y ago
  From the wikipedia: > The triune brain consists of the reptilian complex (basal ganglia), the paleomammalian complex (limbic system), and the neomammalian complex (neocortex), viewed each as independently conscious, and as structures sequentially added to the forebrain in the course of evolution. According to the model, the basal ganglia are in charge of our primal instincts, the limbic system is in charge of our emotions and the neocortex is responsible for objective or rational thoughts. We disproved: - the sequentially added nature - what these zones are responsible for So in the end we're only left with a semi-arbitrary split of the brain in 3 zones and none of the hypothised implications. That to me refutes the hypothesis as a whole, and we're keeping the zone naming by sheer inertia.

by xg15 3y ago

crazygringo 3y ago

OK, but again -- none of that refutes the triune brain hypothesis at all. Literally nobody is claiming that only humans have neocortexes. Nor is anyone claiming it's an indicator of mental capacity. The recent discoveries about crows were interesting, but that doesn't have anything to do with the fact that the neocortex in mammals plays a particular, functional, well-recognized role.

theptip 3y ago
The refutation is of the idea that it’s a strictly chronological layering, with the old layers inside and intact. The correct view is that while the neocortex is indeed mostly new, the “older” more central structures were modified throughout evolution.
- JohnAaronNelson 3y ago
  No one thinks the older structures are static. No one is arguing that. It's a simplified model about the origin. This argument is akin to saying we're not "newer" apes ala > The refutation is of the idea that it’s a strictly chronological ordering of species, with the old species still inside and intact. The correct view is that while homosapiens are indeed mostly "newer", the “older” apes were also modified throughout evolution Obviously.
  - theptip 3y ago
    I mean… the quote from TFA that they are arguing against is > As Paul MacLean (1964), originator of the triune-brain theory, stated, >> man, it appears, has inherited essentially three brains. Frugal Nature in developing her paragon threw nothing away. The oldest of his brains is basically reptilian; the second has been inherited from lower mammals; and the third and newest brain is a late mammalian development which reaches a pinnacle in man and gives him his unique power of symbolic language. And they quote other textbooks that are making claims along these lines too; this is right at the beginning of TFA. So I think you are wrong that “no one thinks that”. Of course they don’t think the old brains are 100% static but there are claims that they are largely conserved.
    - tigen 3y ago
      MacLean doesn't say the brain is an onion with a tiny reptile inside!
    - jacquesm 3y ago
      > there are claims that they are largely conserved. That they're not static doesn't necessarily mean that they aren't largely conserved.
  - Retric 3y ago
    It’s an incorrect and misleading model about the origin. Bat wings and bird wings share many traits but the common answer didn’t fly it’s simply convergent evolution. The brain structures of that same common ancestor is only vaguely related to modern structures in mammals and reptiles. Modern reptiles, birds, and humans have experienced the same amount of evolution. There’s similar traits, but we don’t call whale flippers hands because that’s what the structures was in some of their ancestors or even what it is in related species. Similarly we don’t call human hands flippers because that’s what the structure started out as even further back and it’s still preforming that function in modern fish. The human visual cortex is larger than most creatures entire brain, it’s a wildly different structure than you find on a frog which plays a wider role in cognition than just decoding vision.
makeitdouble 3y ago
From the wikipedia: > The triune brain consists of the reptilian complex (basal ganglia), the paleomammalian complex (limbic system), and the neomammalian complex (neocortex), viewed each as independently conscious, and as structures sequentially added to the forebrain in the course of evolution. According to the model, the basal ganglia are in charge of our primal instincts, the limbic system is in charge of our emotions and the neocortex is responsible for objective or rational thoughts. We disproved: - the sequentially added nature - what these zones are responsible for So in the end we're only left with a semi-arbitrary split of the brain in 3 zones and none of the hypothised implications. That to me refutes the hypothesis as a whole, and we're keeping the zone naming by sheer inertia.