Split Brains: What Happens When You Sever the Corpus Callosum? (Intro Psych Tutorial #36) 

Wow, that's quite interesting, thanks for commenting!

Why not two different lenses? Or differing laser eye surgery?

I'm glad I could help, thanks for commenting!

Glad you enjoyed it, thanks for commenting and let me know if you have any questions!

Kamala I'm glad it helped, thanks for watching!

Haha, thanks, glad it was helpful!

yea i noticed as well. btw the video was very informative thx

You're welcome!

You're welcome, thanks for commenting!

You're welcome, glad to hear that!

@Nadodi Mannan Girl why does this sound like Schizophrenia and less like a spilt brain thing

You're welcome, best of luck on your exam!

PsychExamReview aw thank you! I ended up getting a 95%, only missing 2 questions. I’m very happy about it!

@@CatnipMed That's great, keep up the good work!

You're welcome, glad to hear you're enjoying it!

You're welcome!

You can go further and ask if that's true without the split too

Glad to hear that!

I hope you do better than passing, best of luck!

Great!

Jeremy, did you end up doing this procedure? My daughter's epilepsy team is suggesting it for her. She also has drop attacks several times a day and is always showing some sort of bruise/cut/scrape/burn on her face at a given time. She is only 5.

Wow, I am so glad for you to find out about this so you can consider your options.

Yes, good point, I would certainly agree that the wiring is really for binocular depth perception, not redundancy for losing an eye. But imagining losing an eye and still having information sent to both hemispheres can make the concept that vision is split by visual field rather than by eye easier to remember. Thanks for commenting!

I'm so curious of these after reading your comment!

Great question! The oculomotor nerve controls most eye movements and connects both eyes to the midbrain. This is not severed in these patients, so they don't have changes in their eye movements. Thanks for commenting!

Hope you manage to get your work done but watching educational videos probably isn't the worst way to procrastinate

It might be possible that those are related but I can't really say. I'm not a doctor or neurologist; even if I knew more specific details I still wouldn't be qualified to offer any sort of opinion or medical advice. My only (non-medical) advice is to try to ask questions and learn as much as you can from the doctors or specialists you talk to while recognizing that the brain is incredibly complex and they may not always be able to provide clear answers or understand exactly how things are related. Sorry I can't offer more specific help and thanks for commenting!

This is a good question that I don't really have a full answer to. The general explanation seems to be that the left hemisphere is good at generating explanations for behavior, but the person's belief or doubt in that explanation may be difficult to assess. What we even mean by the "person" may be challenging; the right hemisphere would certainly disagree if it could, but can the left hemisphere doubt its own explanations? I'm not sure what you mean when saying they can't draw from memory though. In my example it's possible that he really had used a key as a screwdriver recently and remembered that, but this still doesn't make it the reason that the left hand drew a key (it drew a key because the right hemisphere saw a key). The left hemisphere attempts to generate a plausible explanation for this event and it may be based in accurate memories, but it's not the real reason, because the experiment design means the left hemisphere can't know the real reason that he drew a key (or whatever other stimulus). The same concept of the left hemisphere generating explanations may be true for non-split-brain people in everyday life too. If someone were to suddenly quiz you on your daily behaviors, you might find yourself coming up with plausible explanations that might not really be accurate. If I were to ask you why you chose a particular menu item or why you chose to stand up from the couch at a particular moment, you might be able to come up with a reasonable justification but that doesn't necessarily mean it was the real reason for the behavior. But it might be very tough to assess how much you sincerely believe those explanations that you generate. I think this leads us to larger questions about the challenges of understanding consciousness that I can't fully address 😅 Thanks for commenting!

You're right, in everyday life split-brain patients are able to move their eyes around and this allows them to send information to both visual fields and thus both hemispheres.

Right, because they travel for some part trough both hemispheres ofcourse. Thanks! This video helped a lot. Will definitely look at more of your videos.

You're welcome!

If the screwdriver is seen in the right visual field then it will be processed in the left hemisphere, which then controls the right hand. So using the right hand, the patient would draw the screwdriver. In this case, since the information is in the left hemisphere, the patient could also say the word "screwdriver" and then both hemispheres would know and then it could be drawn with either hand. This can't be done for information in the right hemisphere though, because the right hemisphere isn't able to produce speech.

@@PsychExamReview Thank you for the prompt response. I understand now!

@@nathalineg9491 I'm glad I could help, let me know if you have other questions!

@@PsychExamReview so both hemisphere hear what he says? how loud he should say it?

It's not a silly question, I think it's a great one that points out an interesting aspect of these studies. When asked, obviously the question goes to both hemispheres for the split-brain patient so we should wonder why only the left attempts an answer (by speaking) while the right doesn't immediately tell the left hand to start drawing or trying to communicate in some way unless instructed. I don't have an answer, but this could be related to Alien Hand Syndrome, which involves losing control over a hand, usually the left hand (right hemisphere). As for the awareness of being a split-brain patient, this also raises some interesting questions about consciousness because while the person can know and remember this information on a conscious level, it's unclear if this affects other unconscious brain processes. A related question is whether a split-brain patient has two separate consciousnesses (one for each hemisphere) or not, and as far as I know, researchers are still divided on this point - pun intended :)

I don't think that this situation usually occurs for those with agenesis of the corpus callosum but there is a lot of variation between individuals and differences in the degree of connection between the hemispheres. They can usually transfer some information between hemispheres but this is impaired and often there are problems with coordination. The early split brain studies by Roger Sperry and Michael Gazzaniga demonstrating hemispheric specialization used participants who had undergone surgery to sever the corpus callosum. Agenesis will influence brain development and may cause some tasks to be more distributed across the hemispheres, which won't have occurred in those who have the surgery later in life. For example, savant Kim Peek (who had agenesis of the corpus callosum) developed language processing in both hemispheres, while someone who had the CC severed in adulthood would likely only have language processing in the left hemisphere.

This tactile input example is based on Roger Sperry's early work with split-brain patients in which he tested both visual and tactile presentations. Here's a somewhat lengthy quote from Sperry (1968) describing these tactile tasks: "A similar separation in mental awareness is evident in tests that deal with stereognostic or other somesthetic discriminations made by the right and left hands, which are projected separately to the left and right hemispheres, respectively. Objects put in the right hand for identification by touch are readily described or named in speech or writing, whereas, if the same objects are placed in the left hand, the subject can only make wild guesses and may often seem unaware that anything at all is present. As with vision in the left field, however, good perception, comprehension, and memory can be demonstrated for these objects in the left hand when the tests are so designed that the subject can express himself through nonverbal responses. For example, if one of these objects which the subject tells you he cannot feel or does not recognize is taken from the left hand and placed in a grab bag or scrambled among a dozen other test items, the subject is then able to search out and retrieve the initial object even after a delay of several minutes is deliberately interposed." Hopefully this helps address your question, you can find the original paper by Sperry here (above paragraphs on page 726 / page 4 of the pdf): sci-hub.st/10.1037/h0026839

The right hemisphere isn't able to control speech, but it has some language processing and the left hand (controlled by the right hemisphere) can indicate responses by pointing. So for something like recognizing a face, the right hemisphere can be shown an image and then be given a choice of what was seen and use the left hand to point to one of the responses. So a face made of books could be shown, then the patient would point to either "face" or "books". The right hemisphere (left hand) will point to "face" while the left hemisphere (right hand) would only identify books because it lacks the ability to recognize the overall face pattern. You can see a demonstration of this with a split-brain patient here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-lfGwsAdS9Dc.html Hope this helps!

PsychExamReview thanks!

This kind of dramatic rewiring doesn't seem to be possible later in life. While the spinal cord does have connections to both hemispheres, there is specialization of these pathways, sending information from the body to only one hemisphere contralaterally and split-brain patients don't show new pathways developing to send information across hemispheres. That said, neuroplasticity for these pathways may be possible very early in development and there are cases of young children undergoing hemispherectomy (surgical removal of one hemisphere) and having the remaining hemisphere take over some of the functions of the missing hemisphere.

I wouldn't think of it as the right hemisphere not being active, it's processing information but it's limited in how it can communicate that processing. It can't speak so it appears silent while the left hemisphere can respond quickly to verbal prompts. As for writing, I'm not sure how well split-brain patients can write with the left hand since language processing is more limited. Generally I've seen pointing to simple responses with the left hand used, I'd have to look into attempts involving writing.

Phillip Wareham I haven't read Waking Up but I'll check it out. As for the nature of consciousness, you're right that it raises the questions of how and why consciousness feels unitary despite containing multiple systems which appear to operate independently. These split brain studies also introduce the question of how much of your sense of self might just be post-hoc explanations of behavior coming from the left hemisphere. Perhaps this can serve as a reminder to think of ourselves as collections of motivations and processes (conscious and unconscious) that somehow converge to create a sense of self that feels unified and in control. One might argue that unity and control are just an illusion, but it seems to me to be a particularly useful illusion and far superior to the chaos of fragmented consciousnesses.

Hi Alexander, essentially any spoken responses coming from a split-brain patient are just coming from the left hemisphere since it controls speech. So the left hemisphere certainly seems to have a fairly fully-developed sense of self. The more difficult part is assessing the right hemisphere because communication using language is necessarily simplified. This makes it much harder to really know what's going on in the right hemisphere. Michael Gazzaniga is one of the leading researchers on split-brain patients so you might start with some of his work. Ian McGilchrist has a book on hemispheric specialization which I've heard good things about but haven't had a chance to read yet. Hope this helps!

The left hemisphere isn't necessarily dominant because the right hemisphere is still receiving and processing information. The right hemisphere just isn't able to control speech, so it can't talk about that information. Communication with the right hemisphere can take place by using the left hand to point at words (it has some language processing), draw pictures, etc. but this communication is certainly more limited. This makes it difficult to assess what's really going on in the right hemisphere, though the fact that the left hemisphere doesn't seem too bothered by the division suggests that the right might not be either.

Lobotomies were far less precise and made many patients worse off. More modern types of psychosurgery are very rare and are only used a last resort when symptoms are severe and other approaches have failed.

I just figured he may use his butt cheeks to communicate :-) Left controls right butt cheek, right left butt cheek. So he may send signals this way. Maybe even Morse code lol ) But probably simple yes/no is enough.... Because right can't process language :-( Maybe it's possible to train it some basic language)

I should clarify that hemispheric specializations aren't trivial when it comes to figuring out how the brain processes information. There's research on activity levels by hemisphere in depression and other disorders that may improve our understanding and perhaps eventually improve treatment options. What I find trivial is popular books and articles encouraging people to do things like "work their right hemisphere" to improve creativity rather than just telling them to "practice tasks requiring creativity". I don't see it as particularly useful to talk about being left-brained or right-brained and this is sometimes used to give an air of scientific credibility just by mentioning the brain. In everyday life we don't have conscious access to each hemisphere's activities and we can't choose to delegate tasks differently once we know about lateralization. So while hemispheric specializations should certainly be investigated and taken seriously, popular books on becoming more left-brained or right-brained should not.

Thank you for the clarification. Yes it would be pseudo scientific to regard abilities/conditions as all reducible to this paradigm of hemisphere imbalance, and that one can improve things by focusing more on the ‘weaker hemisphere’

I'm sorry to hear about your situation. Unfortunately I don't have the expertise to provide specific suggestions and can only suggest you contact medical professionals who might be able to provide more help, thanks for sharing your story here!

I hope your family sued that hospital for malpractice.

@@tiffanyrichardson6698 My family and were never able to find a way to sue. In South Africa- the lawyers and doctors are on the same side. I didn't even get any help with aftercare for the surgeries that I had. I have been in a very bad situation for over 32 years (or it will be 32 years on September 1St). I have also been forced to live an absolutely separated life from my sons- BrianG (nearly 14 years old) and Gregory- (nearly 10 years old- both this month- in a matter of days) who were 5 years old (Brian) and Gregory was 15 months old when they were literally ripped out of my arms and my life. What is so much worse- is that their father was- and is very emotionally and psychologically abusive and how he has treated us (my sons and I by permanently keeping us separated- for what will be 9 years in December). This is excruciating for me beyond words. And their father wants my eldest son vaccinated for the terrible vaccine- which is- or may as well be literal extermination. Please keep my sons in your prayers. I see them- at the most- twice per week- four hours per week- and it is terrible to be forced to live this way. My current husband, Jesse, (who treats me SO much better than their father did for the 10 years we were married)- and I- have tried- with no success- Jesse and I did try to get legal help- and I have tried to get some help with disability- but there is red tape (mostly that the drs. who performed my surgeries in South Africa- destroyed my evidence which shows that the first MRI was not the scan that belonged to me. It is over (or practically 32 years ago- within literal days)- of it being 32 years ago that I had the surgeries. But I still have very bad side effects which makes it nearly impossible for me to get a regular job. I was 17 years old at the time and will be 50 years old next year. This is literally my entire life that my life has been very badly affected. But I miss my sons so much- and it hurts beyond being able to put it to words of how my sons and I have been separated. Please keep them (and us)- and my mom, Claudette in your prayers. My dad passed away just before the PlanDemic started. My mom still lives in South Africa. I have not seen my mom (or my dad- while he was still alive)- for what will be 10 years ago- on August 17 Th. They came for their last visit on the day my youngest son, Gregory- was born. Sorry this is so long, but thank you for your response. May you and your family be blessed. We are living in extra-ordinary times- Biblical- even. It won't be long, now- before Yahshua (Jesus) returns. Help us all if He doesn't. But how can life go on this way for very long?

Laura Wright Partial (or complete) agenesis of the corpus callosum is different from callosectomy in terms of how the brain has developed over time. I described split-brain patients as appearing "normal" in that one probably couldn't tell they had undergone the procedure but there are still subtle linguistic and social effects of this disconnection (which may also be similar to PACC or ACC). I should also emphasize that I'm not a doctor or neurologist and nothing I discuss in my videos should be taken as medical advice. You might like to read this article in which people with agenesis of the CC discuss their diagnoses:blogs.scientificamerican.com/observations/patients-reflect-on-life-with-a-common-brain-malformation/ Thanks for watching!

PsychExamReview - Thank you!

As far as I know auditory messages can't be isolated the way visual messages can be. This is because nerves from each ear are not strictly lateralized and there are connections to the opposite side (contralateral) as well as same side (ipsilateral) hemisphere.

@@PsychExamReview even if they cover the ear?

@@HondaS-fk1mi Yes, nerves from one ear go to the midbrain where there are connections leading to the cortex of both hemispheres. I believe there are more connections to the contralateral side than the ipsilateral side but the messages from one ear are not strictly isolated to the contralateral hemisphere.

The patient can point to words on the screen (with the left hand) to indicate whether he saw a face or books (or whatever objects the face was made of). The right hemisphere has some basic language processing and can recognize words.

@@PsychExamReview thank you very much!

This is a good question and it seems that the right hemisphere does have some basic language processing, even though the left hemisphere is generally where most language processing happens (for most people).

PsychExamReview Ok but only for visual signals we have this language processing right ? Cause we are not able to understand the auditory signals being transferred to our right brain . And does it have to do something with the angular gyrus on that side cause some visual processing do occur there ? I came up with this explanation could u please confirm

@@MEDx_ As far as I know, split-brain patients must be able to understand some auditory signals in the right hemisphere because the right hemisphere can follow instructions (such as being asked to draw something with the left hand) but I don't know the limits of that processing or whether more complex instructions or questions can be understood. As for the role of the angular gyrus, it seems reasonable it could be involved in recognizing written words and it has been suggested that the right angular gyrus plays a role in understanding spatial metaphors. So that might relate to some language processing abilities in split-brain patients but I haven't looked at specific research on this topic. So I don't know well-supported the metaphor idea is or how it might relate to other language processing in the right hemisphere. I simply don't know and can't really confirm.

PsychExamReview yes you are right about that instruction part but I saw it in GUyton and Hall Physiology and I was confused Like it says here “in a teenage boy with sectioned corpus callousum, only left brain can understand both written and spoken words , however right side of brain could understand the written words but not spoken words “. This got me confused that day

@@MEDx_That is a bit confusing, though it could be the case that there are some individual differences in lateralization of language processing that would mean that not all split-brain patients would be identical in their language abilities for each hemisphere.

srinivas anurag If the right hand had held the key or if the left hemisphere had seen the key (presented on the right visual field) then the person would be able to draw it correctly with the right hand. If the left hemisphere had received other information, however, the person would draw (with the right hand) whatever the left hemisphere had seen or felt.

@@PsychExamReview but what if he looks with both eyes and corrects to match to what he saw at right side.

As long as the left hemisphere has received the information somehow (if held by right hand previously) then the person would be able to select the object with the right hand (which is controlled by the left hemisphere).

@@PsychExamReview thank you!!!

Great question. Speaking is mostly controlled by the left hemisphere but the right hemisphere is capable of some language processing and can understand simple instructions.

In this case the remaining eye would still send information from the left visual field to the right hemisphere, and information from the right visual field to the left hemisphere.

That's a great question and there doesn't yet seem to be a definitive answer. One early theory (proposed by Santiago Ramon y Cajal) was that it had to do with the fact that the visual system is inverted (right visual field ends up on the left side of the retina) but this explanation is incomplete. More recent theories are that this cross-wiring (or decussation) resulted from a vertebrate ancestor turning on its back without rotating the brain (known as somatic twist theory) or that it results from two 90 degree turns that occur during embryo development (axial twist theory). These theories focus on how it may have occurred rather than potential benefits though it has also been proposed that crossing over could help to reduce wiring errors.

Excellent recommendation!

You're right that many drugs have been demonized in the past and now there have been some changes looking into how some psychoactive drugs might have therapeutic uses. Thanks for commenting!