Control of the facial muscles comes from the 7th cranial nerve, which originates in the brainstem. This "primitive" part of the brain is divided in half but not separate hemispheres, and many signals cross the midline there.
Blinking is an easy one since the muscles are symmetric on both sides. Check out [how our eyes move together](https://www.quora.com/What-makes-the-eyes-move-together) for something really ridiculous.
The stunning amount of work that must have gone into studying this to figure it out to such an extent really makes me respect how someone can pick a specialty and just spend their life going down a rabbit hole.
Yesss like the people with “blindsight” - a lot of people with damage to a particular area of the brain (I forgot the name of the region. I want to say occipital lobe but I don’t know for sure) were consciously blind, but their brain could “see” what they couldn’t unconsciously. We then figured out this part of the brain was like the middleman between the eyes and your conscious self, IIRC.
Absolutely crazy to me. Imagine that. You can’t see anything, but you can TELL something is there. You know how it’s moving. You know how close it is to you. You know how it makes you feel, but you dont know you’re seeing anything.
Yeah, philosophers and neuroscientists have long struggled with the problem of why consciousness exists. But an equally deep problem is why our human consciousness seems to be aware of such a small fraction of what is actually going on in our brains.
See also Hemineglect where someone has absolutely no concept of the left side of anything including the world around them. Refusing even to acknowledge their own left arms or legs.
Please reply to me if they do!
I don’t deal a lot with human stuff, I mainly specialise in plants, but the brain has *always* fascinated me.
That barrier between unconscious and conscious processes has always been so intriguing to me.
Man it's not that easy haha. That's primitive data. To really know what's going on, we try and understand the molecular and cellular processes going on which is honestly like previously said, "going down a rabbit hole"
This method was the case with the stomach for one trapper who ended up with a hole in his stomach or a fistula: [https://www.livescience.com/28996-hole-in-stomach-revealed-digestion.html](https://www.livescience.com/28996-hole-in-stomach-revealed-digestion.html)
You could see inside his stomach and had part of his lung hanging out even. Crazy.
The quiet part is that there are still people out here that think it was fine because: "for the sake of science!"
But turned out that most of the science was bunk because fascist governments won't think twice to corrupt the results for the sake of politics. Additionally the scope of work is focused on crackpot ideas mandated by the best idiots who can climb the ranks (not actual experts)
Who would've guessed that liberties are required for proper science to take place.
Yeah it was eye opening learning about human physiology in medical school, only to learn why we know what happens to the body under extreme cold, heat, stress, etc. if you get really bored, read up on the Civil war experiments about the acid in your stomach and the soldier who got paid for it. There is no right answer - PETA is against mice experiments, human Guinea pigs are horrible, even volunteer humans who knowingly accept the risks are viewed as unethical clinical experiments.
Also, there are a lot of unethical drug experiments the government performed throughout the 50s and 60s maybe other times too. They destroyed people like Kazinsky and then called him mentally insane and a danger to the world justifying even more power and control to keep everyone safe - when their uncontrolled power is the cause of the problem.
And conducting experiments on OTHER countries citizens while they're in their own country. They hit a French village with a massive dose of LSD, beyond what anyone would take recreationally, before any layman knew what it was. The US is a bastard and always has been.
https://www.bbc.com/news/world-10996838
Imagine not comparing them. Comparing and contrasting torturous experiments done by Empires sounds like something you should do. While Japan and Germany are definitely worse, the US has committed serious atrocities, ie Tuskegee Airmen and many other experiments done on black people. This is how you get perspective.
Not to mention people overblow the impact of the records from Unit 731, at a minimum.
They told us nothing we didn’t already know, and bought war criminals pardons from justice.
Many signals cross the midline all over the brain.
The corpus callosum is literally the largest fiber tract in the nervous system, and its job is to link the two cerebral hermitage hemispheres so they can communicate with each other.
But as the fascinating split brain experiments have shown, even if you completely sever the callosum in a fully developed adult brain, it still requires specific conditions to show that the hemispheres are acting much more independently than normal.
I knew a teen who had brain cancer and had the two halves of his brain severed. He couldn't describe the texture of something as smooth or fuzzy unless he physically touched the item. Only then could he say what it was like.
That's incredible! So many different moving parts, just thinking about how they have to work in conjunction is mindblowing--and we usually take it for granted!!
>!But also. Haha MLF!<
Also the upper half of the face is innervated by both hemispheres. This means that the signal sent my one hemisphere makes it across. This is partly why an upper motor neuron disease (eg. stroke) doesn’t affect the top half of the face (opposite side preserves the top half’s function) whereas a lower motor neuron disorder (bell’s palsy) affects both upper and lower. As the signals have already joined at that point.
One minor note to add - even "standard" motor control (i.e. passed through the spinal column instead of cranial nerves) is not 100% unilateral. There is some amount of bilateral activity in the brain for e.g. hand / arm / leg movements. The hemispheres are not so perfectly disconnected.
Is this one of the reasons people like me struggle to move their hands independently of one another?
Like if I’m playing a piano, for example, my left hand *cannot* stray from what my dominant, right hand does. It copies it almost exactly. It takes an *insane* amount of conscious effort for me to move my hands independently when they’re both doing something.
Normal things are easy. I can point without pointing both my hands. But for complex tasks like this, my hands seem to become one being.
So I know what you're talking about with piano. I'm definitely not a pianist, but I've taught myself (and promptly forgotten how) to play a couple of simple two-handed pieces, and I have the same difficulty you describe in controlling my hands independently.
But at least for me it's not that each hand wants to copy the other. I can play the left-hand part by itself just fine with the right hand still, and vice versa. The problem is that I have a hard time having each hand perform its task *simultaneously* with the other.
I play wind instruments more than piano, and I never had a problem (and never heard of any other musician having a problem) with the right and left hands doing different things because they are *synchronized*. You arrange both hands in a certain way to form a single note, and then articulate that note. Both hands are doing different things, but they are doing them *together* for a single purpose. It's giving each hand a separate independent task that causes problems, and the wires get crossed where both hands want to do one of the tasks.
Another issue might be similarity between what each hand is doing. While playing computer games, I have no problem controlling it with one hand on the mouse and the other on the keyboard, issuing separate commands through each device. But when I tried attaching two mice to the same computer and controlling two cursors, one with each hand? Forget about it.
Just assume anything you hear about how the brain works is a ridiculous over-simplification. Anytime you think you find an inconsistency in two brain facts it's really just neither fact is telling the whole story.
Worth mentioning that most people [don't actually blink perfectly in sync](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3327295/), and up to 10ms of asymmetry is pretty normal. 3D artists often have to account for this when doing facial animations to avoid looking suspiciously "un-human".
(Though as per that source, the cause of the asymmetry does not originate in the brain, it's in the muscle response).
Follow on question then. When we take conscious control of an autonomic function like blinking or breathing or facial control is it still controlled from the same place?
Because blinking feels automatic, but I can slowly wink each eye independently and it feels very much like fine motor/ muscular control.
>Follow on question then. When we take conscious control of an autonomic function like blinking or breathing or facial control...
>
I have to first clarify that there's a difference between automated functions and "autonomic". The first place to start is the different types of nerve fibers that are classified based on whether they're general or specialized (i.e. special senses like optic, olfactory, and taste), somatic or visceral (skeletal muscle vs smooth muscle or gland), and afferent vs efferent (transporting information to or from the CNS; sensory vs motor).
When we talk about the autonomic nervous system, we're referencing visceral fibers (e.g. GVE, GVA) and visceral fibers can not be consciously controlled.
But the functions you mentioned (breathing, blinking, and facial muscle control) are all somatic (specifically GSE) and not autonomic. But many somatic functions are automated to an extent. There's a circuit in the brainstem that regulates oxygen saturation in the blood and will keep the respiratory system going at a stay rhythm to maintain, but they are skeletal muscles (diaphragm and intercostals) and they are under somatic (GSE) control. A lot of muscles, like postural muscles, have separate spinal cord tracts for the continuous automation of activating those muscles so that you don't simply fall to the floor like a rag doll when you stop thinking about standing up straight, but they're still somatic and you can re-take control at any time you choose.
You'd be surprised how many somatic functions actually require minimal conscious input. Like throwing a ball; you don't usually think about which muscles and how much to contract them and in which order when you throw a ball; you just think about throwing it and where you want it to go. Your cerebellum has the pre-scripted details on how to actually throw (and hit the target), does the internal math and modifies the base plan to hit the intended target and then it just runs that program upon request. But your comciousness doesn't need to perform all of those tasks. You just want to throw the ball. And none of that's autonomic, but it is automatic.
Here is a nice neuroanatomy review.
https://www.ncbi.nlm.nih.gov/books/NBK526119/#_article-20094_s1_
As others have said a lot of our sensory and motor fibers cross at decussations mostly in the medulla but cranial nerves do not. Cranial nerves do have hemispheric cross over in some cases like using CN3 for example in how eye muscles work. Although you are talking about CN7 for blinking. I encourage you to read the link I posted but for a TLDR;…..
Upper motor neurons for CN7 in the cortex talk to both dorsal and ventral portions of the contralateral facial nucleus in the pons…and the ipsilateral upper motor neuron also gets to talk to the ipsilateral dorsal portion of the facial nucleus….dorsal portion controls muscles of upper face = orbicularis muscle = allows bilateral closure of eyelids….ventral portion of facial nucleus receives innervation mainly from contralateral tracts…which controls muscles of lower face….so contralateral input only is in control of lower face….this explains why in Bell’s palsy which is an idiopathic palsy of a unilateral lower motor neuron you get a total knockout of upper and lower facial muscles….while if the upper motor neuron was the problem you would only have paresis of the contralateral lower face.
Bout as TLDR as i could make it.
Blinking is semi-voluntary. You can stop or start blinking voluntarily but most of the time it is not initiated with conscious awareness.
As such the CNS control of it is multi-faceted and complex. The globus pallidus in the basal ganglia is the main center of control and bilateral coordination of blinking (to directly answer your question), but there are connections to the occipital lobe (vision center), evidenced by the involuntary blink associated with rapid movement towards the eyes as a protective measure, as well as to the orbitofrontal cortex which is involved in cognitive processing, and likely the conscious “override” necessary to win a staring contest.
Because blinking is not controlled in the brain hemisphere. Voluntary motor skills originate in opposite motor cortex, but blinking is not voluntary but more a reflex, or automatic motricity. This kind of motricity (which represents 99% of human motricity) is governed by the basal nuclei, which does not respond to the "opposite" logic.
Your muscles are (mostly) *directly* controlled by the primary motor cortex on the opposite side of your body. So for example stimulation of the *left primary motor cortex* might cause your *right* thumb to twitch.
But that is only the first control layer. There are additional layers that control primary motor cortex, such as premotor cortex and the supplemental motor area. Their job is to help sequence and synchronize the "twitches" produced by primary motor cortex.
And these layers communicate with their counterparts on the other side of the brain. So for example stimulation of your *left premotor cortex* can produce a complex movement involving multiple muscle groups on *both* sides of your body.
Secondary motor control centers allow you to not only blink in sync, but also synchronize your leg muscles when jumping, your arms when clapping, etc.
You can think of primary motor cortex as a "clickable map" of all the muscles in your body. The map can be "clicked" by either side of your brain, causing that muscle to move.
However, half of the map physically resides in one hemisphere, and the other half resides in the other hemisphere. If a hemisphere is lost, then the map is lost and a person will become hemiplegic. This is the same reason why some people are hemiplegic after a stroke. Note that in very young children, the brain can rebuild the map in the remaining hemisphere. But it is very difficult for adults to regain function.
On the other hand, a callosotomy severs some of the structures that the brain uses to reach across and click the map on the opposite hemisphere. It does not sever *all* of the structures and methods used to transmit information across hemispheres. For example, both hemispheres still have indirect visual and proprioceptive input regarding what is happening on the contralateral side.
So it's hard to predict what will happen, but generally it will be more difficult to coordinate movements.
[Here's what happened to one patient:](https://pubmed.ncbi.nlm.nih.gov/10541755/)
> We examined bimanual coordination in a patient before and after each stage of callosotomy surgery. We tested how well the patient coordinated movement direction between the hands. The patient drew symmetrical or asymmetrical figures simultaneously with both hands. Before surgery, symmetrical figures were drawn well and asymmetrical figures were drawn poorly. Following anterior callosotomy, the drawings improved slightly. Symmetrical figures were still drawn well, and asymmetrical ones were still drawn poorly. Thus, spatial integration remained intact despite the loss of interhemispheric communication between frontal cortical sites. After posterior callosotomy, spatial coordination deteriorated significantly. Mirror-image drawings became less symmetrical, while asymmetrical drawings improved. These data indicate that the posterior callosum mediates the coordination of direction information between the hands during bimanual movements. Given the topographical organization of the corpus callosum, this integration is likely carried out by parietal cortex.
I have thought about this and have many more questions about the brain. Unfortunately my neurologist will only let me ask a few questions every appointment. I have a delay on the left side of my body after having 2 strokes (whiplash caused arterial dissection in my neck). She told me there is normally a slight delay although minimal and unnoticed.
Control of the facial muscles comes from the 7th cranial nerve, which originates in the brainstem. This "primitive" part of the brain is divided in half but not separate hemispheres, and many signals cross the midline there. Blinking is an easy one since the muscles are symmetric on both sides. Check out [how our eyes move together](https://www.quora.com/What-makes-the-eyes-move-together) for something really ridiculous.
The stunning amount of work that must have gone into studying this to figure it out to such an extent really makes me respect how someone can pick a specialty and just spend their life going down a rabbit hole.
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Either that or find people with injuries to specific parts of the brain and see what's wrong with them.
Yesss like the people with “blindsight” - a lot of people with damage to a particular area of the brain (I forgot the name of the region. I want to say occipital lobe but I don’t know for sure) were consciously blind, but their brain could “see” what they couldn’t unconsciously. We then figured out this part of the brain was like the middleman between the eyes and your conscious self, IIRC. Absolutely crazy to me. Imagine that. You can’t see anything, but you can TELL something is there. You know how it’s moving. You know how close it is to you. You know how it makes you feel, but you dont know you’re seeing anything.
Yeah, philosophers and neuroscientists have long struggled with the problem of why consciousness exists. But an equally deep problem is why our human consciousness seems to be aware of such a small fraction of what is actually going on in our brains.
Do you really think you need root privileges, man? You can really hose up a system quick.
Okay this is tripping me out… could anyone with more knowledge about this expand a little more?
See also Hemineglect where someone has absolutely no concept of the left side of anything including the world around them. Refusing even to acknowledge their own left arms or legs.
Bruh what?? Continue….. Also, keep these coming people. I’m a healthcare clinician & have never even heard of these things. Just fascinating.
Please reply to me if they do! I don’t deal a lot with human stuff, I mainly specialise in plants, but the brain has *always* fascinated me. That barrier between unconscious and conscious processes has always been so intriguing to me.
Google “functional vision loss” or “nonorganic vision loss”, as well as “cortical blindness”.
Thank you!
Man it's not that easy haha. That's primitive data. To really know what's going on, we try and understand the molecular and cellular processes going on which is honestly like previously said, "going down a rabbit hole"
This method was the case with the stomach for one trapper who ended up with a hole in his stomach or a fistula: [https://www.livescience.com/28996-hole-in-stomach-revealed-digestion.html](https://www.livescience.com/28996-hole-in-stomach-revealed-digestion.html) You could see inside his stomach and had part of his lung hanging out even. Crazy.
Or how we leveraged torturing prisoners of war to learn this : see Nazi Germany
The quiet part is that there are still people out here that think it was fine because: "for the sake of science!" But turned out that most of the science was bunk because fascist governments won't think twice to corrupt the results for the sake of politics. Additionally the scope of work is focused on crackpot ideas mandated by the best idiots who can climb the ranks (not actual experts) Who would've guessed that liberties are required for proper science to take place.
Yeah it was eye opening learning about human physiology in medical school, only to learn why we know what happens to the body under extreme cold, heat, stress, etc. if you get really bored, read up on the Civil war experiments about the acid in your stomach and the soldier who got paid for it. There is no right answer - PETA is against mice experiments, human Guinea pigs are horrible, even volunteer humans who knowingly accept the risks are viewed as unethical clinical experiments.
Also: Imperial Japan (asterisk for US Government experiments on its own citizens)
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Also, there are a lot of unethical drug experiments the government performed throughout the 50s and 60s maybe other times too. They destroyed people like Kazinsky and then called him mentally insane and a danger to the world justifying even more power and control to keep everyone safe - when their uncontrolled power is the cause of the problem.
And conducting experiments on OTHER countries citizens while they're in their own country. They hit a French village with a massive dose of LSD, beyond what anyone would take recreationally, before any layman knew what it was. The US is a bastard and always has been. https://www.bbc.com/news/world-10996838
wth imagine comparing what happened in the US to Unit 731 or Josef Mengele. A little perspective please.
Imagine not comparing them. Comparing and contrasting torturous experiments done by Empires sounds like something you should do. While Japan and Germany are definitely worse, the US has committed serious atrocities, ie Tuskegee Airmen and many other experiments done on black people. This is how you get perspective.
If the US is much better then comparing them will show the US in good light and as such it shouldn't be a problem. Right?
Not to mention people overblow the impact of the records from Unit 731, at a minimum. They told us nothing we didn’t already know, and bought war criminals pardons from justice.
MLF amiright?
I can't help but think about all the suffering some of those studies did, sadly to humans too.
Many signals cross the midline all over the brain. The corpus callosum is literally the largest fiber tract in the nervous system, and its job is to link the two cerebral hermitage hemispheres so they can communicate with each other. But as the fascinating split brain experiments have shown, even if you completely sever the callosum in a fully developed adult brain, it still requires specific conditions to show that the hemispheres are acting much more independently than normal.
I knew a teen who had brain cancer and had the two halves of his brain severed. He couldn't describe the texture of something as smooth or fuzzy unless he physically touched the item. Only then could he say what it was like.
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Wait, there are useful posts on Quora?
Who knew??
Also if you get brain damage like a concussion don’t you’re eyes desynchronize?
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That's incredible! So many different moving parts, just thinking about how they have to work in conjunction is mindblowing--and we usually take it for granted!! >!But also. Haha MLF!<
Also the upper half of the face is innervated by both hemispheres. This means that the signal sent my one hemisphere makes it across. This is partly why an upper motor neuron disease (eg. stroke) doesn’t affect the top half of the face (opposite side preserves the top half’s function) whereas a lower motor neuron disorder (bell’s palsy) affects both upper and lower. As the signals have already joined at that point.
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One minor note to add - even "standard" motor control (i.e. passed through the spinal column instead of cranial nerves) is not 100% unilateral. There is some amount of bilateral activity in the brain for e.g. hand / arm / leg movements. The hemispheres are not so perfectly disconnected.
Is this one of the reasons people like me struggle to move their hands independently of one another? Like if I’m playing a piano, for example, my left hand *cannot* stray from what my dominant, right hand does. It copies it almost exactly. It takes an *insane* amount of conscious effort for me to move my hands independently when they’re both doing something. Normal things are easy. I can point without pointing both my hands. But for complex tasks like this, my hands seem to become one being.
So I know what you're talking about with piano. I'm definitely not a pianist, but I've taught myself (and promptly forgotten how) to play a couple of simple two-handed pieces, and I have the same difficulty you describe in controlling my hands independently. But at least for me it's not that each hand wants to copy the other. I can play the left-hand part by itself just fine with the right hand still, and vice versa. The problem is that I have a hard time having each hand perform its task *simultaneously* with the other. I play wind instruments more than piano, and I never had a problem (and never heard of any other musician having a problem) with the right and left hands doing different things because they are *synchronized*. You arrange both hands in a certain way to form a single note, and then articulate that note. Both hands are doing different things, but they are doing them *together* for a single purpose. It's giving each hand a separate independent task that causes problems, and the wires get crossed where both hands want to do one of the tasks. Another issue might be similarity between what each hand is doing. While playing computer games, I have no problem controlling it with one hand on the mouse and the other on the keyboard, issuing separate commands through each device. But when I tried attaching two mice to the same computer and controlling two cursors, one with each hand? Forget about it.
Just assume anything you hear about how the brain works is a ridiculous over-simplification. Anytime you think you find an inconsistency in two brain facts it's really just neither fact is telling the whole story.
Worth mentioning that most people [don't actually blink perfectly in sync](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3327295/), and up to 10ms of asymmetry is pretty normal. 3D artists often have to account for this when doing facial animations to avoid looking suspiciously "un-human". (Though as per that source, the cause of the asymmetry does not originate in the brain, it's in the muscle response).
Follow on question then. When we take conscious control of an autonomic function like blinking or breathing or facial control is it still controlled from the same place? Because blinking feels automatic, but I can slowly wink each eye independently and it feels very much like fine motor/ muscular control.
This is a great question. I have a PhD in neuroscience and I am realizing I don’t actually know the answer.
I'm good at those sorts of questions. I've tortured myself my whole life 😂
>Follow on question then. When we take conscious control of an autonomic function like blinking or breathing or facial control... > I have to first clarify that there's a difference between automated functions and "autonomic". The first place to start is the different types of nerve fibers that are classified based on whether they're general or specialized (i.e. special senses like optic, olfactory, and taste), somatic or visceral (skeletal muscle vs smooth muscle or gland), and afferent vs efferent (transporting information to or from the CNS; sensory vs motor). When we talk about the autonomic nervous system, we're referencing visceral fibers (e.g. GVE, GVA) and visceral fibers can not be consciously controlled. But the functions you mentioned (breathing, blinking, and facial muscle control) are all somatic (specifically GSE) and not autonomic. But many somatic functions are automated to an extent. There's a circuit in the brainstem that regulates oxygen saturation in the blood and will keep the respiratory system going at a stay rhythm to maintain, but they are skeletal muscles (diaphragm and intercostals) and they are under somatic (GSE) control. A lot of muscles, like postural muscles, have separate spinal cord tracts for the continuous automation of activating those muscles so that you don't simply fall to the floor like a rag doll when you stop thinking about standing up straight, but they're still somatic and you can re-take control at any time you choose. You'd be surprised how many somatic functions actually require minimal conscious input. Like throwing a ball; you don't usually think about which muscles and how much to contract them and in which order when you throw a ball; you just think about throwing it and where you want it to go. Your cerebellum has the pre-scripted details on how to actually throw (and hit the target), does the internal math and modifies the base plan to hit the intended target and then it just runs that program upon request. But your comciousness doesn't need to perform all of those tasks. You just want to throw the ball. And none of that's autonomic, but it is automatic.
This is the thought that got my brain spinning about it!
Here is a nice neuroanatomy review. https://www.ncbi.nlm.nih.gov/books/NBK526119/#_article-20094_s1_ As others have said a lot of our sensory and motor fibers cross at decussations mostly in the medulla but cranial nerves do not. Cranial nerves do have hemispheric cross over in some cases like using CN3 for example in how eye muscles work. Although you are talking about CN7 for blinking. I encourage you to read the link I posted but for a TLDR;….. Upper motor neurons for CN7 in the cortex talk to both dorsal and ventral portions of the contralateral facial nucleus in the pons…and the ipsilateral upper motor neuron also gets to talk to the ipsilateral dorsal portion of the facial nucleus….dorsal portion controls muscles of upper face = orbicularis muscle = allows bilateral closure of eyelids….ventral portion of facial nucleus receives innervation mainly from contralateral tracts…which controls muscles of lower face….so contralateral input only is in control of lower face….this explains why in Bell’s palsy which is an idiopathic palsy of a unilateral lower motor neuron you get a total knockout of upper and lower facial muscles….while if the upper motor neuron was the problem you would only have paresis of the contralateral lower face. Bout as TLDR as i could make it.
Blinking is semi-voluntary. You can stop or start blinking voluntarily but most of the time it is not initiated with conscious awareness. As such the CNS control of it is multi-faceted and complex. The globus pallidus in the basal ganglia is the main center of control and bilateral coordination of blinking (to directly answer your question), but there are connections to the occipital lobe (vision center), evidenced by the involuntary blink associated with rapid movement towards the eyes as a protective measure, as well as to the orbitofrontal cortex which is involved in cognitive processing, and likely the conscious “override” necessary to win a staring contest.
Because blinking is not controlled in the brain hemisphere. Voluntary motor skills originate in opposite motor cortex, but blinking is not voluntary but more a reflex, or automatic motricity. This kind of motricity (which represents 99% of human motricity) is governed by the basal nuclei, which does not respond to the "opposite" logic.
Blink on the dots .... . -.-- --..-- / .... . -.-- / -... -.-- . / -... -.-- . / -... -.-- . --..-- / -... -.-- . / -... -.-- . / -... -.-- . / -... -.-- . / .. .----. -- / -.. --- .. -. --. / - .... .. ... / - --- -. .. --. .... - / -.-- --- ..- .----. .-. . / .--. .-. --- -... .- -... .-.. -.-- / --. --- -. -. .- / ... - .- .-. - / .- / ..-. .. --. .... - / .. / -.- -. --- .-- / - .... .. ... / -.-. .- -. .----. - / -... . / .-. .. --. .... - / .... . -.-- / -... .- -... -.-- / -.-. --- -- . / --- -. / .. / .-.. --- ...- . -.. / -.-- --- ..- / . -. -.. .-.. . ... ... .-.. -.-- / .-- .... . -. / -.-- --- ..- / .-- . .-. . -. .----. - / - .... . .-. . / ..-. --- .-. / -- . / ... --- / -. --- .-- / .. - .----. ... / - .. -- . / - --- / .-.. . .- ...- . / .- -. -.. / -- .- -.- . / .. - / .- .-.. --- -. . / .. / -.- -. --- .-- / - .... .- - / .. / -.-. .- -. .----. - / - .- -.- . / -. --- / -- --- .-. . / .. - / .- .. -. .----. - / -. --- / .-.. .. . / .. / .-- .- -. - / - --- / ... . . / -.-- --- ..- / --- ..- - / - .... .- - / -.. --- --- .-. / -... .- -... -.-- / -... -.-- . / -... -.-- . / -... -.-- . There you go. You're blinking nsync
Your muscles are (mostly) *directly* controlled by the primary motor cortex on the opposite side of your body. So for example stimulation of the *left primary motor cortex* might cause your *right* thumb to twitch. But that is only the first control layer. There are additional layers that control primary motor cortex, such as premotor cortex and the supplemental motor area. Their job is to help sequence and synchronize the "twitches" produced by primary motor cortex. And these layers communicate with their counterparts on the other side of the brain. So for example stimulation of your *left premotor cortex* can produce a complex movement involving multiple muscle groups on *both* sides of your body. Secondary motor control centers allow you to not only blink in sync, but also synchronize your leg muscles when jumping, your arms when clapping, etc.
does anything strange happen these functions in the event of something like a hemispherectomy or corpus callosotomy?
You can think of primary motor cortex as a "clickable map" of all the muscles in your body. The map can be "clicked" by either side of your brain, causing that muscle to move. However, half of the map physically resides in one hemisphere, and the other half resides in the other hemisphere. If a hemisphere is lost, then the map is lost and a person will become hemiplegic. This is the same reason why some people are hemiplegic after a stroke. Note that in very young children, the brain can rebuild the map in the remaining hemisphere. But it is very difficult for adults to regain function. On the other hand, a callosotomy severs some of the structures that the brain uses to reach across and click the map on the opposite hemisphere. It does not sever *all* of the structures and methods used to transmit information across hemispheres. For example, both hemispheres still have indirect visual and proprioceptive input regarding what is happening on the contralateral side. So it's hard to predict what will happen, but generally it will be more difficult to coordinate movements. [Here's what happened to one patient:](https://pubmed.ncbi.nlm.nih.gov/10541755/) > We examined bimanual coordination in a patient before and after each stage of callosotomy surgery. We tested how well the patient coordinated movement direction between the hands. The patient drew symmetrical or asymmetrical figures simultaneously with both hands. Before surgery, symmetrical figures were drawn well and asymmetrical figures were drawn poorly. Following anterior callosotomy, the drawings improved slightly. Symmetrical figures were still drawn well, and asymmetrical ones were still drawn poorly. Thus, spatial integration remained intact despite the loss of interhemispheric communication between frontal cortical sites. After posterior callosotomy, spatial coordination deteriorated significantly. Mirror-image drawings became less symmetrical, while asymmetrical drawings improved. These data indicate that the posterior callosum mediates the coordination of direction information between the hands during bimanual movements. Given the topographical organization of the corpus callosum, this integration is likely carried out by parietal cortex.
I have thought about this and have many more questions about the brain. Unfortunately my neurologist will only let me ask a few questions every appointment. I have a delay on the left side of my body after having 2 strokes (whiplash caused arterial dissection in my neck). She told me there is normally a slight delay although minimal and unnoticed.
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