I disagree with the author's interpretation of this.
As a neurologist myself, I was taught it was specifically to simplify visual processing, although there may be other theories but this is what I was taught. Like others commenting here, the way the lens works in each eye is by flipping the image onto your retina. If we had only one eye, there would be no issue, the image would appear as a continuous image, just flipped around. However, because we have two eyes, they both individually flip different fields, thus separating the continuity of the image horizontally. If you try drawing out various different ways to try and remedy this problem of binocular vision, the way nature's approach is quite elegant in reuniting the image as well as separating visual processing into left/right.
The way it works is by separating the left and right fields of each eye, and then crossing them so that the left fields goes to the right half of the brain and the right fields go to the left half of the brain. Each right/left half is now interpreted by one side of the brain and the image is again continuous if you draw it out on the brain. Of course now each side of the brain sees the opposite side, but we remedy this by crossing everything else so it plays well with visual interpretation. Now the right side of the brain sees, senses, and controls the left side of the body and vice versa.
When it comes to everything else, there isn't a clear benefit for having processing swapped to opposite hemispheres. But visual processing benefits from it greatly, and so the rest of the nervous system goes along with it.
I don't think you understood the author's interpretation well enough to say you disagree with it.
The problem you describe, of mapping binocular vision is an example of the topological problem described by the author. But it's not the only example: feeling nerves, for example, have the same symmetrical problem with mapping your skin sensations to the physical space, and your hearing also is "binocular" (there's actually a separate word for this, "binaural"). The visual problem you're describing is part of the topological problem. You're describing the same problem, but you're describing a part of the problem.
Where you're just wrong is on two points:
1. "When it comes to everything else, there isn't a clear benefit for having processing swapped to opposite hemispheres." Wrong. As mentioned before, binaural hearing also needs to map a 3d topology to a 2d topology from two data collection points, and skin needs to map a 3d topology from many more points (but also symmetrical). Additionally, the effect works on "outputs" as well as "inputs", mapping the 2d space to a 3d space so that you can control symmetrical tools such as your arms and legs means that the swapping is needed when sending signals outward as well.
2. "[V]isual processing benefits from it greatly, and so the rest of the nervous system goes along with it." Vision is not the evolutionary driver here. The criss-crossed neurology predates the existence of vision in our evolutionary heritage. The article mentions worms, for example: how does your hypothesis explain why their nerves crossed hemispherically given they don't have lenses and retinas?
I think the eye example is in fact different because light passing through the lense is inverted onto the retina as the root comment explains, there's no such inversion for perceiving other senses. I find the explanation intuitively appealing at first, but given connections are criss crossed for far simpler animals such as worms like you mention, I don't think the idea that vision is the primary driver of this phenomenon is correct.
It's not different, because the left-right flip by the lens is part of a rotationally symmetric image translation (that also flips up for down, e.g.), not a bilaterally symmetric reflection. With the rotation, there is no change in the relationship of parts of the image one to another, relative to our personal orientation, the way there is in the reflection, so it's trivial for the brain to account for it - up on the retina is always down in the real world, left on the retina is always right in the real world, etc.
I think the point you're making is that orientation of the image is arbitrary, and the original commenter agrees that's the case for one eye: "If we had only one eye, there would be no issue, the image would appear as a continuous image, just flipped around."
But we have two eyes, so if you directly connect the two inverted images observed by each retina, there would be a discontinuity in the middle of the joined image (peripheral light from the outer sides of each eye would be mapped to the middle of the joined retinal image). The original commenters point was that criss crossing the neural connections from the retina would resolve this discontinuity, allowing the brain to process a continuous image.
Those kind of light receptors don't have the lenses that cause our eyes to flip the image. They are omnidirectional and usually not even on the surface of the critter. Just a small bag of rhodopsin that triggers a nerve to depolarize. I think the geometric arguments in the article make sense in that context as well, the same way they would for a chemotactic or pressure sensor.
I only have one eye (retinoblastoma) and have never been able to see through my left eye, you can't imagine the amount of questions that just arrived in my head, do you have some material to explain this a bit more? Specially in regards to the flipping different fields? Thanks so much!
I agree that we don't know, but we can weight the different possible explanations by plausibility.
The article's explanation would explain all the facts we do know, so we can reasonably weight that as a very plausible explanation. I'll also add that the article says, 'Now, this all makes sense mathematically, but it’s important to note that we don’t know for certain that this is truly why our brains and bodies are connected the way they are. There is very little biological research on this intriguing question. The convenient dodge often heard is that the scientific method tells us “what,” not “why.”'
The GP's explanation doesn't explain why worms have criss-crossed nervous systems despite not having retinas or lenses, and it incorrectly assumes that other systems don't benefit from a criss-crossed nervous systems, so we can reasonably weight the GP's explanation as highly implausible.
> we can [weigh] the different possible explanations by plausibility
that's not science. we have no idea what is plausible or not, really, and we should not forget that. we can make up reasons that seem reasonable or which makes sense when combined with other unproven hypotheses but we simply do not know and we should not be offering up any words other than "we don't know" when asked for explanations.
> we have no idea what is plausible or not, really, and we should not forget that. we can make up reasons that seem reasonable or which makes sense when combined with other unproven hypotheses but we simply do not know and we should not be offering up any words other than "we don't know" when asked for explanations.
You're saying "we have no idea what is plausible or not" and then go on to describe what plausibility is.
The one part of your definition of plausibility that you're leaving out is observation, which is critical. We aren't just comparing hypotheses to other unproven hypotheses, we're comparing hypotheses to what we observe.
We observe that criss-crossed nervous systems predate eyes in the phylogenic record, so from that observation, we can fairly conclusively say that criss-crossed nervous systems did not evolve as a result of eyesight. You can say that this is implausible, unreasonable, or doesn't make sense--I don't particularly care which terminology you prefer, but they're all saying basically the same thing: we know (i.e. have high degree of confidence) that a criss-crossed nervous system did not result from eyesight.
I'm not sympathetic to Platonic idealist arguments that "it's not possible to know anything" because that's a completely useless way of thinking, which even the people saying it don't believe. If I offer a philosopher the opportunity to get punched in the face, they'll decline my offer, because they know from prior experience that getting punched in the face will be an unpleasant experience. You can't reasonably claim that it's impossible to know anything in conversation when all the choices in your life are based around the things that you know. Platonic idealist epistemology is a convenience argument that people only trot out when they want to disagree with something.
Additionally, the idea is self defeating: if it's impossible to know things, then how do you know it's impossible to know things?
hypothesize all you want, imagine the causes all you like, I don't care, but don't say you know, when you don't, that's all.
if you don't know, and you're talking to a layman audience, don't say you know. don't pretend you know, don't even present guesses, even when they are framed as guesses, because people will hear you saying you know.
"we think [educated guess] but we don't know" is the only acceptable phrasing, to me.
Remember this: science can never tell you when your hypothesis is correct. science can only ever tell you when your hypothesis is wrong.
I think the entire world has forgotten this.
Richard Feynman explains it very well in this lecture, particularly in the bit starting at 20:04.
> if you don't know, and you're talking to a layman audience, don't say you know. don't pretend you know, don't even present guesses, even when they are framed as guesses, because people will hear you saying you know.
> "we think [educated guess] but we don't know" is the only acceptable phrasing, to me.
I understand that it's irresponsible to communicate a greater degree of confidence than is supported by the evidence, but I'm saying that it can also be irresponsible to communicate a lesser degree of confidence than is supported by the evidence.
Consider, for example, the statement "vaccines don't cause autism". There is absolutely no evidence that vaccines cause autism (and if you want to argue that, go elsewhere--I'm not going to argue with assholes). Saying "we think vaccines don't cause autism, but we don't know" is irresponsible, because you have people saying, "Vaccines cause autism! I'm 100% sure!" A layman audience, hearing both people, hears that one isn't sure, and the other one is absolutely sure, and so they believe the absolutely sure one. The result is unvaccinated kids, the revitalization of nearly-extinct diseases, and widespread human death and suffering.
Pedantically using words that, by their dictionary definition, mean a certain thing, doesn't result in quality communication. If you say words that pedantically mean the truth, but fail to produce the true belief in the minds of your audience, you've failed to communicate. That's not entirely your fault--some of the responsibility for communication rests on the listener--but if you can improve your chances of communicating the truth by speaking with confidence that is supported by the evidence, it is your right and perhaps even obligation to do so.
> Remember this: science can never tell you when your hypothesis is correct. science can only ever tell you when your hypothesis is wrong.
This is trivially wrong:
Let's say your hypothesis is "vaccines cause autism". According to what you just said, we can't prove that hypothesis correct, we can only prove it wrong.
So let's say we've proven wrong the hypothesis, "vaccines cause autism". Now consider the hypothesis "vaccines don't cause autism". Haven't you just proven that hypothesis correct?
> I think the entire world has forgotten this.
Don't you mean "I think the entire world has forgotten this, but I don't know"? /s
Cut the melodrama. You're not so special that you have some unique or even rare knowledge that everyone else has forgotten. Lots of people know a hell of a lot more about science than either you or I do.
The Feynman video you linked doesn't load the video for me.
Here is the same video on youtube, in much worse quality. maybe this will work. I've linked to the correct timestamp, but if that doesn't work, seek to about 19:50 and listen for ~60 seconds: https://youtu.be/phfaDMEMFaU?t=1189
well Feynman said the same thing I did. I quoted a single sentence in that lecture.
to elaborate on that point a tiny bit more: science cannot prove itself correct; science can only ever prove itself incorrect, because if your theory is incorrect, future experiments will eventually reveal that. if your theory is correct, you won't ever be proven correct, you will simply never be proven wrong.
this isn't about language and who is sure and who is not, this is about lying.
it's true that there is no evidence that vaccines cause autism. it's also true that scientists have looked and looked and looked for that link, and found nothing at all. with current technology and understanding, there is no link, and no one can prove a link between the two. no one can prove that link exists; not even those who are absolutely sure it exists.
see? no lies, no hyperbole, no guesswork, and the facts are clearly communicated.
To be mobile and agile in a three dimensional world, a creature needs to be able to process information about its environment such as adjacency, and direction - that is, the relationship of different parts of space, or things in space, to one another, matters a lot to the organism. You could store store each individual perceivable bit of spacial information randomly, but then to get this structural information you'd need an elaborate mapping layer that allowed the brain to compute distance and direction. It's far simpler to rely on actual spatial relationships in the cortex to model the structural information by mapping it to an analogous spatial structure information. Simpler means less energy in construction and operation of the facility, and that wins out in an evolutionary race.
This just seems like conjecture. There is already a mapping layer between the specific nerve activation and spatial information. A random mapping wouldn't be any more or less efficient in that regard.
I could see something like going from one to two eyes causing this. When having one eye, you'd have a random nerve mapping. It's advantageous to have two eyes over one, but if the optical inputs for two eyes were to be randomly remapped, then the evolutionary knowledge stored in the single-eye mapping would be lost. So it would advantageous to map the optical nerves from two eyes in a way that mostly fits the single-eye mapping. Obviously, this is just a random theory without any evidence. I offer it only as an example of a logical argument as to why the spatial orientation of an object would affect the spatial orientation of the nerve mapping.
> Of course now each side of the brain sees the opposite side, but we remedy this by crossing everything else so it plays well with visual interpretation.
Why? I don’t understand the logic of what you’re theorising. If your right side is damaged, why does having your ipsilateral side help? How common would this have been from an evolutionary perspective? And if your right side is damaged, and it’s taken out your right brain, now you’ve got a right side that doesn’t work and a left side you can’t control
I kind of get the idea: if damage is coming to one side of the body, then the sensory data reporting it would be better handled by putting the brain half dealing with it on the opposite side, to give it a chance to react rather then also be damaged.
But, I think the visual processing explanation is more compelling - since it seems unlikely this scenario would arrive in enough non-catastrophic situations to be evolutionary significant.
That was my intuitive first thought, but a healthy left brain stuck trying to control a crippled right body is a worse situation than a healthy left brain controlling a healthy left body and merely deadweight on the right.
Thanks for the explanation, it makes much more sense than the original article and the attached image was not even necessary for me to "get" the idea while many paragraphs and diagrams just left me confused before reading it.
The flip is both vertical and horizontal. Imagine all the rays converging at the focal point and carrying on. Each ray ends up on the opposite side of the centre of the image. Up->down, left->right, etc.
Tangentially related to this is when I installed a patio in my yard two summers ago. Okay, let me explain:
I had a sugar maple about 3 feet away from where I had to dig the foundation for the patio. An arborist said that it’s a bit close but the maple is strong and it should recover fine.
I cut out a bunch of roots and within a month the exact sections of the canopy corresponding to the roots I cut went brown.
It was incredible to me how the roots relate directly to the canopy. I always kinda thought it was one big circulatory system, where everything supports everything. I expected the whole tree to struggle a bit.
Next season the tree was fully recovered.
The neurological system seems to work the same way? It’s a directed graph where one root supports a very specific set of branches? I guess the circulatory system is like that too if you separate the two sets. Nature doesn’t really like cyclic graphs, does it?
> I cut out a bunch of roots and within a month the exact sections of the canopy corresponding to the roots I cut went brown.
Root systems in general (for trees at least) mirror what's happening above ground. Pruning trees is a beneficial intervention, as it causes the corresponding roots to die and decompose. This not only makes precious biomatter available for recycling by the microorganisms in the soil, but also releases chemical signals that cause the tree itself and neighbouring plants to send out new growth.
When I worked for the park service, my botanist boss told me that the reason junipers and that sort of scrubby, stress-tolerant tree have twisty trunks is so that if they lose a section of roots they don't lose a sector of sunlight in the canopy. Because sunlight can be focused on one side of a tree (especially if growing on a steep slope), a twisting trunk can save a tree in the case of root damage on one side.
> Nature doesn’t really like cyclic graphs, does it?
I had a course in computational neuroscience as part of my bachelor's and one of the things that we covered was that the timing of fires is important, in that depending on how soon before or after a neighbouring neuron fires, the connection may be weakened or strengthened. This is called Spike-timing-dependent plasticity:
> Under the STDP process, if an input spike to a neuron tends, on average, to occur immediately before that neuron's output spike, then that particular input is made somewhat stronger. If an input spike tends, on average, to occur immediately after an output spike, then that particular input is made somewhat weaker hence: "spike-timing-dependent plasticity"
From [1].
The implication of that, I believe, is that it prevents short cyclic graphs, for the sole reason of avoiding feedback loops that can cause the brain to go haywire (lol) due to the feedback loop. It sounds like an evolutionary adaptation to prevent short-circuiting.
From Hebbian Learning, we have that the cycles would become easier to trigger, meaning that it is a feedback loop that increases efficiency, however, without a mechanism to prevent this cyclical feedback loop, the brain could be filled with cycles that eventually turn to just rings, which is probably not a desirable property.
If anyone knows more about this please tell me. If it's a new idea, please remember to add my name :')
just keep inmind, this, and other phenomenon dont happen in all neurons, or in any particular neurons 100% of the time.
neurons change functional, and structural state, depending on past events [hysterisis] and will shut down/modify state activities depending on feedback from post synapic neurons.
also neurons will get tired and handoff activity to similar neurons in a cohort.
Its very much not a directed graph. We do have brain loops. That's where brain waves come from, circular paths of neurons activating themselves in a circular firing squad.
There's a theory that says an ancestor of all vertebrates just flipped its head around and it stayed that way. (Source: https://arxiv.org/abs/1003.1872). Can someone who knows more about animal physiology explain this paper? Thanks.
But that issue is related to the fact that insects have their nerves in the inferior part of their bodies, and the digestive tract on top, while we have our nerves in the back (protected by bones), and the digestive tract on the front, which would be the lower part if we were still walking with four limbs.
The issue described here is left-right symmetry, and it also applies to insects, so it is more general.
So far I have read that these are related theories and the "somatic twist" theory is an expansion on the earlier theory of inversion. And there seems to be another related but separate theory called the axial twist theory (explained in the linked paper).
I had always presumed this was the reason, and just assumed that crustaceans, insects, etc. didn't have bilaterally crossed nervous systems. However, the linked article mentions nematodes also having a nervous system with bilaterally crossed connections, so it can't be the entire story (and it seems my assumptions about crustaceans, insects, etc. is wrong).
This should be the top comment here: a reference to an actually scientific analysis that uses an argument that is plausible from an evolutionary perspective.
E.g.: someone else here was arguing that maybe the mirroring helps the brain keep processing inputs from the side that was hit. Evolution does not work this way! Flipping doesn’t “just” happen, that’s a huge morphological change. It had to have evolved incrementally, with each intermediate step having an immediate benefit.
The paper explains how and why this may have occurred.
> Flipping doesn’t “just” happen, that’s a huge morphological change.
In some primitive ancestor, it might have 'just' happened randomly. Some mutations that are small in genetic code terms can have huge effects on body structure.
You say that, however, there is still no convincing scientific explanation for irreducible complexity in evolution. Interestingly, this paradox is exemplified best by the irreducible complexity in the nature of the eyes
> irreducible complexity in the nature of the eyes
There have been several papers published that outline how eyes could have evolved via a series of incremental steps.
I don't have references handy[1], but the process is thought to go something like this:
1. The earliest, primitive animals were tiny. Think small worms and the like.
2. Soft-bodied creatures are always at least somewhat translucent to light, at least to a certain depth: a few millimeters at least. Just shine a torch through the thin part of your hand between your thumb and forefinger! Similarly, this is why you know it is daylight or not even with your eyelids closed.
3. If a nerve in the brain of a primitive creature contains a chemical that is both neurologically active and light sensitive, then even without any "eye structure" at all, it can detect lightness and darkness. Melatonin is thought to be a candidate for this chemical. This can happen by accident but is immediately useful for seeking shelter, escaping a "sudden shadow" (predator), detecting day/night cycles, etc...
4. If those nerves migrate closer to the surface of the skin, then they receive more light, and the sensitivity becomes directional. The most obvious thing is for a spot to develop on top of the head, which is still seen in many creatures today!
5. Having multiple such spots over an area, sensitivity increases.
6. If that light-sensitive patch becomes concave[2], then this provides crude directional sensitivity. The more concave it becomes, the more accurate the direction sense, until it invaginates completely to form a cavity with a small hole as the pupil -- a pinhole camera. There are creatures living today with similar primitive eyes!
7. If the cavity becomes filled with a transparent variant of the skin, then it can be protected from filling up with dirt, etc...
8. If this transparent flesh has uneven index of refraction, it can focus light. This is a primitive lens.
9. Etc...
You get the idea. Essentially, every step can occur incrementally, providing benefits at every step, and these steps are littered throughout the tree of life, we just have to put the steps back in order to see the timeline.
I'm surprised the article and comments haven't mentioned the axial twist hypothesis [0], which IMO is the best explanation I've seen so far for contralateral wiring. The axial twist hypothesis has experimental evidence and is also predicted from physical first principles of what is known about embryonic development. It explains the central decussation, which is a stronger prediction than the existence of some decussation (from what I understand of the article). I still don't quite understand how one gets from the existence of a decussation between two distinct body-cortex paths to contralateral organization, but maybe after reading the paper I will get it.
After an explanation that without L/R crossing the body map in the brain would be flipped upside down, comes this revealing passage:
"To make sense of the sensation [...] your brain would have to switch from one somatotopic map to another one with the opposite z-axis orientation".
This a textbook example of the "Cartesian theater" fallacy. It assumes a little person inside the brain who has to deal with an image projected upside-down. Of course that doesn't make sense.
Slightly related: there’s a YouTube video [1] of a guy teaching himself how to ride a bicycle “in reverse”, i.e. you turn left, and it goes right. It takes some practice but in the end it just “clicks”. So now he’s balancing and moving completely opposite to perception.
So you’re right about the little man. I struggle to see why some arbitrary axis transform is “too hard”.
I vaguely remember reading about some similar experiments with goggles that mirrored vision. As I remember, after a few days, people can mostly overcome the difficulties of having their vision reversed.
to counteract your point though he does struggle a lot, and he does find riding the bicycle the usual way very hard after that. if you watch the video you can see him falling over and over
But that’s probably because it’s two sets of muscle memory competing for the exact same space. It’s like when a new game decides to reinvent controls, and every reviewer slams it for “janky controls”, because we have years of training in a particular layout. That’s why we have the concept of “unlearning things”, because the brain is really good at learning things, even wrong things. But that sounds to me to be an entirely different discussion than “brain orientation”.
The pictures with the finger at the end are even more confusing. They conflate the mapping from body parts to cerebral cortex (the cortical homunculus) with the mapping from the homunculus to some other part of the brain were the 3D environment is allegedly mapped. They don't make sense to me.
I still don't buy it. Once you cut a person vertically in two half with a guillotine, you get two topological disks of skin. Each disk can be mapped into the 2D surface of the brain. It doesn't matter if the parts of the skin are in the same plane or rotated 90°.
Obviously some parts of the skin are stretched, so a 2D map will cause a lot of deformation. Also some parts of the skin are more sensitive than other and will need more brain surface. But this is what is happening, there are a few maps in the brain https://en.wikipedia.org/wiki/Cortical_homunculus and they are quite deformed, and they even have a few cuts here and there.
Once you decide to cut the map in two parts, each part can be projected in both orientations without geometric problems.
Maybe related, maybe not, but I noticed this quote is incorrect:
> Odd things happen when we [project 3D space onto a 2D surface]. On a 2D map, an airplane taking the most direct path between two cities appears to travel in an arc, and satellites orbiting the globe appear to oscillate in a sinusoidal path
If you use the Gnomonic projection then all great circles become straight lines.[0] The only "catch" is that you need to cut the Earth into two hemispheres.
Once you cut the person in two halves, it's easy to map the half to a plane.
Imagine a sphere. You cut it in two halves, and you get something like this https://en.wikipedia.org/wiki/Nicolosi_globular_projection and use a scissor to cut it in the middle. Now imagine the initial sphere is made of rubber and it contracts to a body glove thigh around the person.
There are no discontinuity inside each half. Just a huge discontinuity between the two halves, but each one is processed by a different side of the brain anyway.
The projections in each half can be made in both orientations, the one that is like the skin and the mirror one. The non-mirrored is difficult to wire, but the mirrored one is easy to wire.
About the discontinuity, there is a huge discontinuity between the two sides of your body that are processed by the two sides of your brain, and you don't notice it.
Moreover, in each eye, there is a discontinuity because each half of each of your eyes is proceed in a different side of your brain https://www.quora.com/Which-side-of-the-brain-does-the-optic... With that hardware I expect to see a black vertical line in the middle of my eyes, but the transition is quite smooth.
I don't find the TFA explanation convincing; it's too abstract.
I like the explanation in terms of predator avoidance behavior. Imagine a primitive fish with eyes that can detect motion. If it sees something moving, usually it wants to get away from that thing. If you see something moving in your left eye, the best way to swim away is to send a signal for a muscle contraction in your right side, which will cause you to curl and swim to the right. So the best wiring is a direct connection from left eye to right side, and right eye to left side. The brain is built up starting from that kind of connection.
But sensory input is also reversed. If you're touched on the right side of your body, it projects to the left side of your brain, which then projects back to the right side of your body again. If the goal were to minimize wire length, everything would stay on the right side.
> I don't find the TFA explanation convincing; it's too abstract.
...meaning you didn't understand it.
It may not be a good explanation, but the problem isn't that it's too abstract.
> If you see something moving in your left eye, the best way to swim away is to send a signal for a muscle contraction in your right side, which will cause you to curl and swim to the right. So the best wiring is a direct connection from left eye to right side, and right eye to left side. The brain is built up starting from that kind of connection.
If your fish only contracts the right side of it's body, that's not going to create effective motion, and while your fish is having the seizure you've described, it's going to get eaten.
Even if there were some sort of direct eye-to-muscle connection (which there isn't) the left eye would connect to the right side of the brain, which would then connect to the left side muscle, so you'd have left eye to left muscle (via the brain), not left eye to right muscle.
This is my take. With two sensors connected crosswise to musculature that pushes forward, you get goal seeking for targets in front and avoidant behaviour for targets behind.
It's what our ancient ancestors had. And they were successful, and elaborated on that theme, and by the time they were complicated enough to start thinking "hey wait, why is our nervous system crossed up like this" it was too much bother to uncross it.
You're just making shit up. There's zero evidence for this.
You also don't seem to understand that inputs (senses) are also crossed, meaning that in your hypothetical inputs-directly-tied-to-outputs scenario, the movement produced would be in exactly the opposite direction to what you're describing, i.e. toward the predator.
And even if you found a way to resolve these problems, movement is far more complex than you're describing, and practically requires a more complex structure between sensation and reaction to coordinate muscular contractions which produce movement. The sort of reflexive muscular contraction you're describing would look more like a seizure than a contraction which produces useful movement.
I'm all for preferring the simplest explanation which explains our observations, but your explanation doesn't explain what we observe in any way.
> Letters on your T-shirt appear reversed for the same reason that the name “Quanta” would appear flipped, as “Quanta” if you wrote it with your finger on a frosty window and then went outside to look at it.
I'm amused at the audacity of the author for asking the webdevs to manually wire up a unique HTML span with a custom CSS transform solely to make a single word appear to be rendered as though seen in a mirror. :)
It's the inline style is in a hidden div at the end of the story and within #postbody, I suspect the author did it -- it's part of the story content at least -- and so didn't need the webdevs to do anything different. It's a nice touch.
A theory I heard that I like, is that if you are getting attacked from the right, and suffer damage to the right side of your head, you probably want your right arm to work more than your left for the highest chance of fighting off the attack.
If your brain is hurt to that degree on either side, you are unlikely to be able to continue to fight. Evolution doesn’t usually work to offset unusual events like this. It is more about optimizing operations on a daily basis.
But maybe you get a few more seconds, one more swing, and take out your opponent. Your tribe kills the lion or wins the war. If the initial mutation wasn't detrimental so wasn't tested right away on an individual basis, but allowed to reproduced to form a population, it would be the group test that gets passed. Just a thought.
it should? natural selection progresses through the reproducers that survive. the ones that could attack on their right side for right side attack survived?
Survived with severe brain damage. Are they going to be able to survive for much longer to reproduce? It sounds that feature is only useful in a very specific circumstance. Evolution is usually happy with good enough. It seldom does micro optimisations like that
> Since Quanta is a nonprofit foundation-funded publication, all of its resources go toward producing responsible, freely accessible journalism that is meticulously researched, reported, edited, copy-edited and fact-checked. And our editorial independence ensures the impartiality of our science coverage — our articles do not reflect or represent the views of the Simons Foundation.
I read some brain encyclopedia ages ago, so details are a bit foggy, but when the connections between the two hemispheres of the brain gets injured/damaged it can have some really strange effects.
In the book they retold tests where they did things like showing a picture of a shovel to only one eye and ask the person to think of a garden tool, and they'd say shovel. Then they'd ask the person to explain why they're thinking of a shovel, and they'd tell some elaborate story like having met their neighbour a few days ago who said that they need to buy a shovel, or something similar. This due to the connection between the part(s) of the brain that constructs the story having severed connections to the parts the receives and processes the visual input of that eye. There was a few hundred pages of tests like these with wildly different effects depending on where the connections had been damaged.
Without injury the input should be shared just fine, but since the difference is so severe when the connections are damaged I guess (with no credentials or so to back it up) that there could be some hard-to-measure differences in thoughts formed depending on which eye is used.
An intressting thing with that, is that the side of the brain that controls speech might be completly accurate. It could have said showel cause that side of the brain thoght of its neighbors shovel. The only thing that it would be missing would be that it was influenced to think of that shovel event by input given to the other brain half.
A severed corpus callosum - sometimes done to mitigate the effects of sever epilepsy (the seizure on one side of the brain can't travel to the other side).
Normally when you look into your own eyes in a mirror they are each looking into themselves.
If you cross your eyes and get the distance just right, you can look into each eye from the other.
For me it causes a strange effect, or seems to. I would be interested to hear reports from others of their subjective experience of doing that?
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Edit to add: Reading aloud also has different effects than reading silently. I surmise that the extra feedback loop from voice to ear has something to do with it.
A common proofreading trick is to read your writing aloud. You catch errors that are [negative hallucination?] elided by, uh, non-external loops.
Your auditory memory is a different space than other forms of memory, so when you read aloud to yourself it permits you to buffer additional information and get to it later, in addition to mapping it through different perceptual space as you’ve noted. So at least the perceptual circuit and the time constraints are changed by doing so.
I find that it no longer works very well for me though: I often read aloud without experiencing or remembering anything I’ve read at all. It’s the same autopilot that takes over driving.
A life hack I found useful: if I need to remember a few numbers for a few minutes before I can write them down, I keep quietly repeating them in my mind. It works much better for me than trying to memorize them since I think it uses auditory memory; after a few repetitions the sequence of words becomes automatic and easy to repeat without thinking.
"Some of the most famous examples of confabulation come "split-brain" patients, whose left and right brain hemispheres have been surgically disconnected for medical treatment. Neuroscientists have devised clever experiments in which information is provided to the right hemisphere (for instance, pictures of naked people), causing a change in behavior (embarrassed giggling). Split-brain individuals are then asked to explain their behavior verbally, which relies on the left hemisphere. Realizing that their body is laughing, but unaware of the nude images, the left hemisphere will confabulate an excuse for the body's behavior ("I keep laughing because you ask such funny questions, Doc!")." https://www.edge.org/response-detail/11513
For others interested, look up Roger Sperry's split-brain experiments[1], done at CalTech. He received the 1981 Nobel Prize for the work. I'm surprised the above article doesn't mention it.
We don't cut cut peoples' brains in half any more, so it was a unique moment in time when they had people available with this condition, and the results are quite illuminating.
Cutting (or partially severing) the corpus callosum connecting the hemispheres of the brain has been shown to have some interesting results along those lines, though: https://en.wikipedia.org/wiki/Split-brain
That is such a wild idea. I wonder if you dance with one eye covered or learn a language solely thru input from right vs. left eye (and ears) would it matter? Or what about musicians like Jimi Hendrix who played their instrument backwards?
It seems un-testable in terms of eliminating any sort of placebo/expectation effect though.
Various corrective surgeries for vision over the years have intentionally mismatched focal distance between eyes. Presumably there are at least tens of thousands of people that can only read up close with one eye, and at a distance with the other.
I personally was born with a crossed eye. It's been corrected, but the reading acuity of my secondary eye is worse than my primary. Everything is in focus optically, but reading is more strenuous. It's almost as if there's some letter or syllable sized gaps my brain is interpolating around. Perhaps I only notice it when reading because of the density of high frequency content in all the letters.
Be wary, in my personal case it was neck tightness restricting blood flow to the face and jaw. Normally you should be able to make a square by touching fingers to your opposing shoulders and touch wrists to your nose with no pain or tightness, I could not.
I understand that 2d brain to 3d brain connection requires an intersection (criss-cross) I drew that on a piece of paper. But I didn't really get why that has to be the case with 3D brain to 3D brain mapping. I am able to connect them without a need for an intersection. Are there easier examples to understand the intuition behind this hypothesis?
The real reason is much simpler: first step in evolution is 1 ligt sensor connected with 1 muscle. If the eyes sees danger you need to swim away from it. If you see food you need to swim towards it. Food was initially abundant l. Do moving your right muscle would cause you to move toward the food.
> The nervous system is cross-wired [...] I asked my doctor last week why this should be, all I got was a shrug. So I asked Catherine Carr, a neuroscientist at the University of Maryland, College Park. “No good answer,” she replied.
After reading the piece, as he's proposition a potential theory based on mathematics and elegance of the solution, her reply still feels totally apt. That makes the title slightly misrepresent what he's trying to convey. We don't get the why, just a maybe.
Otherwise I'm not sure 3d mapping simplicity is enough of an answer when the brain can also adapt to way more complicated configurations when receiving partial damage for instance. It also feels like we have very few organs that developped along the most simple solution
The recurrent laryngeal nerve too I'm not sure if it's all or most or some animals. It loops around the heart like a noob PC builder's first build and poor cable management. Giraffes have the best most extreme example of this.
> While there are lots of solutions to this wiring problem, the most elegant is to have two bilaterally symmetrical systems of wiring between the brain and the body, with the connections from each side of the body crossing the midline.
Wouldn't a 3-D brain mapping also solve this issue? Do we just have this flipped symmetry because neural nets started out non-3-D in simple organisms, and we have all just inherited the 2-D structure as our brains have grown? Were there ever 1-D neural networks, and if so, how did they work?
I also didn’t follow the leap requiring animal experience to represent 3D phenomena in 2D mapping in brain space — it feels like an oversimplification in order to force the peg to fit the hole.
I think it has to do with the brain being built up in layers. Even though our brains are 3-D in shape, the layers are effectively thick 2-D surfaces. This is just a guess though.
the problem is mirror image one, when mapping sensory field stimlus, to cortical field state.
as far as 1-d networks are concerned, electrical excitation is not an absolute property of neurons. unicellular organisms employ variations of electrical potential to initiate, coordinate, and buffer functions, and future changes of state.
> the problem is mirror image one, when mapping sensory field stimlus, to cortical field state.
For 3-D mapping onto 3-D I don't understand what you're saying. Except for vision, for which I understand there are optical properties that require image flipping and inversion.
light bounces off objects and travels through the lens of the eye.
when light exits the lens it is inverted, so things to your right are projected on the left side of the retina, the left retinae then communicate contralaterally to the right optical cortex.
sensory field is the snapshot state of each neuron in a 2-d array.
cortical field is same but it is now destined for processing.
left and right fields differ by paralax and this difference is used, to construct a 3-d percept
My theory, this is not about crisscrossing but about splitting. Splitting is done to avoid shared state. Non shared state is crucial for individuality. Other senses - hearing, touch, smell are wired in the same splitting way - hearing from the left ear is processed in both brain hemispheres, so is hearing from the right ear. Now the problems with digital photos is that they are the very thing the brain wiring avoids - a single non-split capture, this is the cause of confusion on a mass scale. This is gravely amplified by recent advances in "AI" object renderings. Brain or unconscious has no tags to differentiate between real and artificial. I have multiple experiences of software systems displaying artificial splitting and duplication, I also experienced duplication of objects in the real world. If anyone knows anything about such experiences or can correct errors in this comment or provide further clearer explanation, please do. I believe some quantum phenomena can be at play here too. I also experienced double stereo hearing, my hearing was as if I heard two separate stereo inputs, as if I had four ears. I have aphantasia, if that matters.
Not that I fully disagree, but this reply is of limited helpfulness. I don't think quantum phenomena can be ignored within the context of human body. I don't know what happens with double-slit experiments, how the sight of it is encoded in the body memory. Software developers have great tools for assuring and checking source code correctness, but the situation for meat-space bodies is very different in practice. Unless you live in some advanced techno-utopia with access to advanced medicine. I don't know where to look for help. I can't run fsck-brain /dev/brain on me.
From the point of view of quantum mechanics your body is very 'noisy'.
You only see quantum mechanical effects, like what you see in the double-slit experiment, in essentially undisturbed systems. That's why when you 'measure' which path the photons take, the interference pattern in the double-slit experiment fails to occur. Your body having lots and lots of atoms sloshing around at body temperature is analogues to taking measurements. It 'collapses' the wave function, if you pardon me using terminology from the Copenhagen interpretation.
It reminds me of the routing for an integrated circuit to do a Fast Fourier Transform. The butterfly operation on which an FFT is based involves a crossover, so the basic problem in routing a planar chip is how to make all those crossed over connections. It would be pretty cool if the brain was doing an FFT!
I once read that an ancestor of ours evolved to have its head rotated 90' relative to its body (like a flatfish or something), but then later when it evolved a normally aligned head again, instead of twisting back 90' the way it had come it just twisted another 90'degrees
I have always assumed that bilaterally symmetric animals have neural cross-wiring so that the two hemispheres of the brain are forced to cooperate more than they otherwise would. Simple animals are prevented from, say, hoarding resources selfishly and maladaptively on the right.
this would be dependency of new structure, on founding structure, and methods.
a plan is developed early,and departure from that initial architechture, is a scorched earth style revision, versus patching old proven fixes,on new hardware.
its a tendency of biological systems to innovate one step at a time, as persistence is a demand, so the system is not overhauled large scale, that would be tantamount to major negative selection, thus non-persistent properties.
My guess is that this enables crosstalk between the nerves which would have been entirely absent otherwise. And crosstalk between left and right sides of the brain is beneficial evolutionarily.
Why is the brain's representation of the 3d world 2d? Wouldn't it be more natural to map the infinity of space, body included, onto a (topologically open) ball in the brain?
As much as I like Quanta Magazine, they dropped the ball on this one. I didn't understand anything of the summary of the paper. I hope they attach some images to the next piece about topology...
this may be effective, when the time comes to allow a synthetic, to have a mobile body, that must model its sensory input to a common format to parse against a stored data array, in order to decide what scheme to employ when negotiating a physical, 3+d world using 2-d arrays of neuromime excitation.
Odd that in the entire explanation they completely ignore embryology and the pathway dependence that came with evolutionary progression between species
As someone with a high signal lesion in the genu of the corpus callosum caused by childhood head injuries I think the brain split in two halfs is simply an impact "kill switch" for severe adult head injuries.
Ergo extreme impact trauma to the head results in the brain breaking the connections between the two hemispheres at the corpus callusom, resulting in immobolisation. However this could also be a temporary kill switch which immobolises the body until such time as the brain's neuroplasticity has restored the corpus callosum.
In such a condition the individual would likely be left for dead, be going hungry and quite likely thirsty which creates an increase in phagocytosis which in turn causes an increase in h2o2 and then catalase the enzyme from the liver breaks this down to water and oxygen, ergo the conditions to help the body live, if not in a slimmed down form (pun intended) still exists and lends credence to fasting.
I think it evolved to be crisscrossed, likely non crisscrossed ones were just eliminated, I’m guessing for redundant reasons. Having it cross covers a bigger area and may serve to cover issues if part of the other side get severed.
As a neurologist myself, I was taught it was specifically to simplify visual processing, although there may be other theories but this is what I was taught. Like others commenting here, the way the lens works in each eye is by flipping the image onto your retina. If we had only one eye, there would be no issue, the image would appear as a continuous image, just flipped around. However, because we have two eyes, they both individually flip different fields, thus separating the continuity of the image horizontally. If you try drawing out various different ways to try and remedy this problem of binocular vision, the way nature's approach is quite elegant in reuniting the image as well as separating visual processing into left/right.
To avoid a large text explanation, this is a simple diagram of the concept how the brain reforms the arrow. https://nba.uth.tmc.edu/neuroscience/s2/images/html5/s2_15_1...
The way it works is by separating the left and right fields of each eye, and then crossing them so that the left fields goes to the right half of the brain and the right fields go to the left half of the brain. Each right/left half is now interpreted by one side of the brain and the image is again continuous if you draw it out on the brain. Of course now each side of the brain sees the opposite side, but we remedy this by crossing everything else so it plays well with visual interpretation. Now the right side of the brain sees, senses, and controls the left side of the body and vice versa.
When it comes to everything else, there isn't a clear benefit for having processing swapped to opposite hemispheres. But visual processing benefits from it greatly, and so the rest of the nervous system goes along with it.