#corpus callosum

[crustacreation]

sorry for the inactivity ! been working on alot. also forgot i had social media

[mcbonypants]

guess whos been locking in on renders recently!

[educatedh0rses]

Long time no see. If I remember I’ll just start posting my backlog of things I’ve drawn

[thejakeformerlyknownasprince]

Hey sorry, what was that in the tags about humans having two brains?? I haven’t read any of the Visser books…

So in Visser, Edriss describes her first experience in the human brain as:

Then I discovered something strange and disturbing. A huge, deep chasm. It seemed to separate the human brain into two halves. And between the halves was only a nerve bundle not much thicker than my own true body... This second half of the brain was an almost mirror image, but not. It could have functioned all on its own, if necessary, and yet it was in some ways radically different in its memories, its sensory interpretation, even its will. Two almost entirely functional brains in one skull, communicating across a channel of nerves. Not a fully redundant system, almost a second, different brain! ...This brain worked by dialectic. Each half of the brain saw and heard and smelled and touched a slightly different world. Each tended toward specialization, but not a hard, fast split. The left half had more language, but not all the language. The right side had more spatial perception, but not all of the spatial perception... This brain contained its own traitor!

And that's a pretty accurate description of how human brains work, and how they differ from those of non-mammals. It's not about individuals being "right brain" or "left brain" (that's nonsensical; anyone who says differently is selling something). It's talking about the fact that the two halves of the brain are partially but not fully redundant, meaning they work as a team. That way there's backup for the super-important functions like breathing, but not for the nifty-not-necessary ones like language.

I think the stuff about the two halves talking to each other from slightly different worlds refers to split brain research. Split brain patients are those who've had that "nerve bundle not much thicker than [a yeerk]" severed in order to prevent seizures. These individuals tend to have normal quality of life (improved after the surgery)... unless you cut off their ability to use sensory information to compensate for the lack of brain-to-brain information. This interview with one such woman says:

neuroscientists now know that the healthy brain can look like two markedly different machines, cabled together and exchanging a torrent of data. But when the primary cable is severed, information — a word, an object, a picture — presented to one hemisphere goes unnoticed in the other.

If you shut a split-brain individual's right eye, then show their left eye the word "baseball", then they can grab a baseball out of a box by touch — but only if they use their left hand. When asked out loud "What did you grab?", they'll answer "I don't know" because they don't — the right hemisphere which controls the left half of the body has almost no language comprehension. If you show the right eye only the words "stand up", most patients will stand, but when asked why, will say things like "I guess I wanted a bathroom break" or "I must be getting restless" because they have no conscious awareness of being told to stand.

Anyway, this system is pretty great, since it means humans can have pretty good quality of life with huge chunks of their brains missing. And it's kinda baffling, because there have also been people who had all quality of life destroyed by minuscule localized damage. Our brains really are their own traitors. Le sigh.

[genderless-girl]

[harpagornis]

Did multituberculates and co have a corpus callosum?

Filikomys reconstruction by Misaki Ouchida. Multituberculates are now thought to have been intelligent mammals, so this discussion is worth having.

Modern placental mammals have something marsupials and monotremes lack: a corpus callosum. This allows for connectivity between the brain hemispheres and thus higher intelligence (though marsupials might be more clever than we give them credit for, and birds lack a corpus callosum and are next in line for civilization). Its thus worth to ask: did extinct non-placental groups have a corpus callosum?

On one hand, the fact that only placentals out of all amniotes have one would imply that this is a feature exclusive to them. On the other hand, marsupials and monotremes both produce undeveloped, fetal young, so they could have secondarily lost the corpus callosum as part of their simplified development. Extinct groups like multituberculates not only were as intelligent as placental mammals but had parts of their braincase not seen in other mammal groups, so it's not unreasonable to assume either the corpus callosum was a mammal synapomorphy and lost on multiple groups or it developed independently. Or maybe multies and co didn't have one and simply got smart via other ways like birds.

Hopefully future finds (or genetic and developmental studies in living mammals) answer this.

[revretch]

Hey Rev I know hivemind stuff is normally based on like bees and ants and such, but my understanding is that it's not really a 1:1 with what we see in media. That being said, what's the actual truth of how these systems work, and is there a real world equivalent that works something like old-school dnd mindflayers?

To be honest, nothing in nature is a true hivemind--not even your own brain. Not every part of the network is immediately hooked up to the others, and it can take a variable amount of time for information to get through to all of it, depending on how your brain is wired.

The effect is most apparent in large animals without corpus callosums (bridge between the hemispheres of the brain)--so, most non-mammal vertebrates. It takes so long for information to get across that, by blindfolding first one eye on a baby duck, then the other, they were able to get it to imprint on two different parents.

The same thing happens with humans that were born without corpus callosums or had them damaged or removed, too, sometimes resulting in Alien Hand Syndrome--a hand you can't control. Effectively, two brains in one head. (Emphasis on "effectively," since information does sync up across the hemispheres eventually.)

In the end, it's all just a matter of how quickly information disseminates, and how obedient the nodes in a network are. Even without telepathy, speech is a way of disseminating information. When we're in sync enough, humans are close enough to hiveminds on their own--and since our communication is so advanced, perhaps the closest to a hivemind of any multicellular creature.

Sources: https://www.sciencedaily.com/releases/2016/11/161117150513.htm

https://www.brainandlife.org/articles/what-is-alien-hand-syndrome

https://www.nature.com/articles/s41467-020-17540-7

[dare-g]

*Corpus Callosum (2002)