View Full Version : Split Brain, One Consciousness


Bowser
02-27-11, 01:46 AM
Reading a page tonight, I discovered something interesting about the nature of consciousness. It seems that people who have had split brain surgery do not experience two separate consciousnesses, even though their two halves appear to be working independently of each other.

http://www.macalester.edu/psychology/whathap/ubnrp/split_brain/Split_Brain_Consciousness.html


As discussed in the experiments on split brain patients, if a perception does not go to the left hemisphere (our center for speech) the patient says they are not conscious of it. (see a standard experiment for a review) However, his right hemisphere is aware of it and can respond accurately. For example, if the person in the experiment was asked to use the object, he would be able to accurately use the key, or if asked to write down the name of the object, the left hand would be able to write the names of simple objects. Even so, the person says they do not know what the left hand is doing. This seems to tell us that we may become conscious of something only if the information about it reach the circuits that control speech in the left hemisphere. It seems that the consciousness of the right hemisphere is largely disjoint from that of the left, the right forms a kind of unconscious mind for the left. It can be disputed that the right hemisphere is not as conscious as the left because it manifests its consciousness in other ways. The right hemisphere has an unconscious knowledge of the stimuli that is presented to it.



According to the above, it would seem that consciousness is seated in the left hemisphere of the brain near the speech center. However, this doesn't appear to be the case when a hemispherectomy is performed on the left hemisphere, which would suggest that consciousness is migratory within the brain.

http://www.time.com/time/magazine/article/0,9171,836175,00.html

jmpet
02-27-11, 02:01 AM
http://www.solhaam.org/articles/humind.html

This is a rather old article that's been a favorite of mine for many years. It's worth sharing here.

Stoniphi
02-27-11, 07:03 AM
As I recall it, consciousness usually starts out seated in the right hemisphere then migrates to the left hemisphere as we age. This can be noted as our emotions become less angry and hostile due to the increasing influence of the left amygdala which seats the more positive emotions and the lessening influence of the right amygdala.

Billy T
02-27-11, 07:40 AM
... it would seem that consciousness is seated in the left hemisphere of the brain near the speech center. However, this doesn't appear to be the case when a hemispherectomy is performed on the left hemisphere, which would suggest that consciousness is migratory within the brain. ... IMHO, most of this conclusion is due to an over identification of "consciousness" with internal speech (or verbalized speech that honestly reflect the thoughts of the internal /silent speech). Daniel Dennettís book Consciousness Explained being an extreme case of the very questionable identification between {internal} speech and consciousness.

There are many cases where speech is lost* due to strokes, yet consciousness clearly is not. When a left hemispherectomy is done, "consciousness definitely" does not "migrate" - only an ability is lost and it may be learned by the right hemisphere, especially in the very young when learning and plastic brains are normal.

At JHU hospital many years ago, when I had some connections with a couple the neurosurgeons, there was a young (< 2 years old, as I recall) girl with Status Epilepsies who had one hemisphere (the left as I recall) removed. When she was older (say 10) she was essentially normal - only careful testing reveled her defects.

SUMMARY: This view that consciousness = internal speech only reflects how little man understands what is consciousness or how it is achieved.

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* If stroke is in Wernicke's area, then speech comprehension is mostly lost and the produced speech is "fluent word salad." If stroke is in Broca's area, then there is no more loss of speech than if the tongue were cut out. I.e. full comprehension, and internal speech is preserved, but the necessary motor coordination to produce speech is lost. In neither case is "consciousness lost" - only communication abilities (extreme for a Wernicke stroke) are lost.

Bowser
02-27-11, 12:46 PM
As I recall it, consciousness usually starts out seated in the right hemisphere then migrates to the left hemisphere as we age. This can be noted as our emotions become less angry and hostile due to the increasing influence of the left amygdala which seats the more positive emotions and the lessening influence of the right amygdala.

But that would leave a person with out consciousness who has had their left hemisphere removed.

Bowser
02-27-11, 01:55 PM
Here's a study that suggests consciousness is a process involving a larger part of the brain rather than a specific area.

http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1000061

Still, there's no explanation why split brain patients don't exhibit dual consciousness.

Stoniphi
02-27-11, 04:39 PM
The pivotal word is "seat". Persons who lack 1/2 of their brain situate their consciousness in the remaining portion.

Occam's Razor - parsimony would indicate there is no need for 2 seats of consciousness so it most likely won't happen.

Billy T
02-27-11, 06:23 PM
... Still, there's no explanation why split brain patients don't exhibit dual consciousness.If consciousness is more related to qualia, as I think it is when contrasted to awareness or the internal speech then split brain individuals often do have split consciousness. - For exmple it is possible to show different scenes (or even different movies) to each brain half. One can evoke the qualia of anger in one half brain and the other sadness. etc. I.e. how we are feeling, what were are experiencing emotionally, can be different for each half.

One also see some thing like this in the alien hand syndrome - one hand under conscious control will grasp the other "alien hand" to prevent it from some inappropriate action, etc.

Billy T
02-27-11, 06:32 PM
Here's a study that suggests consciousness is a process involving a larger part of the brain rather than a specific area.

http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1000061

Still, there's no explanation why split brain patients don't exhibit dual consciousness.Much of your links results were know long ago in "dicottic listening" experiments where one attends to / is conscious of / the audio presented to one ear, yet the meaning of ambigious terms in that attended audio stream is strongly controlled by their presence in the stream you are not conscious of if context there makes their meaning clear.

This of course did not tell anything about what part of the brain was being used -only that both stream were processed to a high level. The brain does many things and consciousness is only informed of a few.

drumbeat
02-27-11, 09:55 PM
It's like 2 separate brains, but the final decision is down to the left-side.

Some people have had damaged brains that has left them with both sides with equal influence, and had such problems as 'Alien Hand Syndrome' where the left hand (controlled by the right brain) moves seemingly of its own accord.

billvon
02-27-11, 10:15 PM
According to the above, it would seem that consciousness is seated in the left hemisphere of the brain near the speech center. However, this doesn't appear to be the case when a hemispherectomy is performed on the left hemisphere, which would suggest that consciousness is migratory within the brain.

That's assuming that there is a discrete location for consciousness. I don't believe that there is. Is there one computer that is the Internet? Where is the Internet located? If you determine that one computer is the Internet, and you disconnect it, and the Internet continues to function (albeit with some impairment) - does that mean the Internet is migratory?

Or is the function that the Internet performs scattered throughout all the parts of the network?

Consciousness is almost certainly an emergent property of a complex neural network, and as such doesn't really have a "central location" of consciousness. It's not a part that can be isolated; it is a property of the system as a whole.

Bowser
02-27-11, 10:29 PM
That's assuming that there is a discrete location for consciousness. I don't believe that there is. Is there one computer that is the Internet? Where is the Internet located? If you determine that one computer is the Internet, and you disconnect it, and the Internet continues to function (albeit with some impairment) - does that mean the Internet is migratory?

Or is the function that the Internet performs scattered throughout all the parts of the network?

Consciousness is almost certainly an emergent property of a complex neural network, and as such doesn't really have a "central location" of consciousness. It's not a part that can be isolated; it is a property of the system as a whole.

I'm just following the path presented by the information available when starting this thread. I did, however, post a link in this thread to a page that would seem to support your theory. I ran into the page after starting this thread.

The implication is that consciousness may still survive even in the most severe cases of brain damage.

Twine
02-28-11, 12:52 AM
Reading a page tonight, I discovered something interesting about the nature of consciousness. It seems that people who have had split brain surgery do not experience two separate consciousnesses, even though their two halves appear to be working independently of each other.

[...]

According to the above, it would seem that consciousness is seated in the left hemisphere of the brain near the speech center. However, this doesn't appear to be the case when a hemispherectomy is performed on the left hemisphere, which would suggest that consciousness is migratory within the brain.

I don't think the quote you gave implies that consciousness is in the left hemisphere. It should be completely obvious that the speech center can't receive any information about your right brain being conscious of something. It could be possible that the right brain is conscious (meaning, experiences qualia) of certain things, but can never communicate this through speech.

I'm curious as to what a split-brain patient would write with either hand if you asked them "Can you speak?"

When the writer you quoted says
"This seems to tell us that we may become conscious of something only if the information about it reach the circuits that control speech in the left hemisphere. It seems that the consciousness of the right hemisphere is largely disjoint from that of the left, the right forms a kind of unconscious mind for the left."he does *not* mean to say that your brain has one consciousness. What he is actually saying is that "the consciousness of the right hemisphere" is separate from the left, and that the left brain is not conscious of things experienced by the right brain. Of course, this should be obvious.

That writer is not saying "people who have had split brain surgery do not experience two separate consciousnesses", but rather is saying "the left brain of people who have had split brain surgery does not experience two separate consciousnesses"

Fraggle Rocker
02-28-11, 12:12 PM
Cetaceans obviously cannot "sleep" the way other mammals do or they might drown. So they have evolved the unique ability for each hemisphere to sleep independently while the other takes care of business. I wonder what goes on when the sleeping hemisphere wakes up. Do they have a meeting to catch up on the news?

Billy T
02-28-11, 12:32 PM
Cetaceans obviously cannot "sleep" the way other mammals do or they might drown. So they have evolved the unique ability for each hemisphere to sleep independently while the other takes care of business. I wonder what goes on when the sleeping hemisphere wakes up. Do they have a meeting to catch up on the news?Sharks must swim to breath (force water thur slits that unlike fish can not move gill flaps to pump it thru) They too sleep each half of the brain separately so they can swim from birth until death.

Fraggle Rocker
02-28-11, 02:37 PM
Sharks must swim to breath (force water thur slits that unlike fish can not move gill flaps to pump it thru) They too sleep each half of the brain separately so they can swim from birth until death.I didn't know that fish, much less the primitive cartilaginous fish, sleep. They have such tiny forebrains, I didn't realize it was divided into hemispheres. What does that make, about eighty-five brain cells on each side? :) So then do all chordates sleep? Seems like a real disadvantage in that environment unless you're the apex predator.

Billy T
02-28-11, 03:22 PM
I didn't know that fish, much less the primitive cartilaginous fish, sleep. They have such tiny forebrains, I didn't realize it was divided into hemispheres. What does that make, about eighty-five brain cells on each side? :) So then do all chordates sleep? Seems like a real disadvantage in that environment unless you're the apex predator.Yes fish sleep. It may not be identical to our sleep with different sleep states. E.g. there is little or no evidence to suggest REM sleep* in fish, but when you think about it REM sleep is detected by the electrical artifacts associated with mussels moving the eyes. Fish at least as a general rule don’t move their eyes much so there electrical REM signals, if existing, would be small and hard to detect.

““Researchers have now been able to show not only that [zebra] fish sleep, but that they can suffer from sleep deprivation and insomnia. By repeatedly disturbing the fish using mild electric shocks, researchers were able to keep zebra fish awake at night. Those fish that had suffered a disturbed night were found to catch up on their sleep as soon as the opportunity arose.”” From http://bigquestion.wordpress.com/2008/03/04/how-do-fish-sleep/

Also see:
http://www.newton.dep.anl.gov/askasci/bio99/bio99047.htm

Having a tiny brain would not seem to me to make it more difficult to sleep – perhaps easier? Bats certainly sleep (and upside down at that) and their brains must be smaller than a shark’s.

*I don’t know but strongly suspect that normal REM sleep is absent in congenitally bind humans too. They may move their unseeing eyes, but not as in normal REM sleep. What would be interesting to know is how these periods of movement are distributed during the night. For example in concentrated intervals that are more common before waking up? I am almost sure congenitally bind humans do dream, but their dreams must be more tactile etc. than a sighted human’s dreams.

PS I learned about shark sleep years ago. As I recall, the researcher did have micro electrodes into each side of their brain. (And presumably a strapped on recording system - I don't recall.)

billvon
02-28-11, 05:42 PM
Sharks must swim to breath (force water thur slits that unlike fish can not move gill flaps to pump it thru) They too sleep each half of the brain separately so they can swim from birth until death.

So? We must breathe each minute or so to live, and yet we sleep for 8 hours at a time. We don't need to "sleep each half of our brain" so we can keep breathing. Automating breathing isn't much different than automating swimming.

Billy T
02-28-11, 07:57 PM
So? We must breathe each minute or so to live, and yet we sleep for 8 hours at a time. We don't need to "sleep each half of our brain" so we can keep breathing. Automating breathing isn't much different than automating swimming.So you say, but I will stick with the known facts -sharks sleep half the brain as swimming is not that automatic - perhaps so they don't try to swim upon the beach or into a boat? Also swimming takes considerable energy so when doing it, finding food or a mate etc. with no more energy is well combined with just breathing from an energy POV.

chimpkin
02-28-11, 10:29 PM
So? We must breathe each minute or so to live, and yet we sleep for 8 hours at a time. We don't need to "sleep each half of our brain" so we can keep breathing. Automating breathing isn't much different than automating swimming.
Yeah, but you can be in a vegetative state-lose higher function, and the brainstem will still keep you breathing if it's working okay.

I think what the sharks do would be more like those people who get in the car and sleep-drive on Ambien or something.

I think bats are smarter than sharks...sharks are pretty dumb.

Hmm, I wonder if there's been any cases of Dissociative-Identity people having major head injury and losing someone in there?
Just a thought.

I don't know that I experience myself as...entirely unitary? or maybe it's just really noisy in here...but there is sort of a me and a not-me that is also me and the conversations get spoken aloud in many instances.

I also don't feel like I'm the same person that I was 20 years ago, I just happen to share exact history with that person. If I have a personal "growth spurt" I could be a different person again in a year or two.

billvon
02-28-11, 11:08 PM
So you say, but I will stick with the known facts -sharks sleep half the brain as swimming is not that automatic

If you remove a shark's brain, it still swims. (Ref: NOVA show from about 10 years ago - they removed a reef shark's brain, attached it to a frame, and moved it slowly through the water; it swam.)


Also swimming takes considerable energy

Sharks are one of the most efficient animals on the planet. Merely sitting comfortably at room temperature, a human uses nearly 5 times as much energy (per unit of body mass) as a great white shark actively swimming in a cold ocean.

http://www.elasmo-research.org/education/white_shark/metabolism.htm

Billy T
03-01-11, 12:50 PM
If you remove a shark's brain, it still swims. (Ref: NOVA show from about 10 years ago - they removed a reef shark's brain, attached it to a frame, and moved it slowly through the water; it swam.)....That "swimming" is without purpose. Only a learned pattern reflex.

Yes, many animals can for brief time mechanically continue well developed motion procedures* but that is not all they normally do when moving - they have some objective to their normal motion which the brainless automaton does not.

The brain feels no pain when it is cut or even if it is sucked out. The brain of an adult cat can be totally removed by suction with only local anesthesia to the scalp. If it is then stood up and some movement of its legs that approximates normal walking is applied, the cat will continue to walk - until it runs into some obstacle, like a wall or chair, which causes it to fall over. I am not sure of the details. Perhaps the "reptilian brain" is not removed.

In some medical research it is not possible to give a general anesthesia as that would invalid the acute test of the drug, etc. so brains are sometimes removed instead. At JHU hospital I was one of two developing new procedure on cat, which would leave it in rather sad state, if we did allow it to recover consciousness, so when we were finished, we simply "put it to sleep" permanently.

That was the first and only time I did that. It was particularly hard to do as that cat, raised from birth in the hospital's animal lab for experimental purposes**, was the most beautiful cat I had ever seen - totally intense black, with very shinny fur. - I can still see it in my mind.

* Legend has it that the pirate, Blue Beard was told that every one of his lined up men he ran past after they cut his head off would be spared. He ran towards the executioner and his sharp sword at the start of the line and saved 4 or 5 of his men, before ceasing to run / collapsing. I donít know if this is true, but it is plausible from what I do know. I have seen a movie of a brainless cat walking.

** Before you get too upset about this, note you probably eat animals raised from birth for you to eat and we were part of an effort trying to help humans with sever neurological problems - such as several epileptic seizures each hour or chronic refractory (to drugs weak enough to leave them conscious) pain.

Fraggle Rocker
03-01-11, 02:59 PM
Having a tiny brain would not seem to me to make it more difficult to sleep Ė perhaps easier?I didn't mean that having a smaller forebrain (not a smaller brain) would make it harder to sleep, just less necessary. The hindbrain never sleeps and AFAIK the same is true of the midbrain.
I am almost sure congenitally bind humans do dream, but their dreams must be more tactile etc. than a sighted humanís dreams.I suppose that would depend on the specific details of their blindness. If the brain centers that process vision are still operational then they might very well exercise during sleep. But since they have no portfolio of actual sights to correlate, they may be random signals or perhaps even an organized vision that is nothing like the real world. Maybe they dream in abstract art. ;)
So? We must breathe each minute or so to live, and yet we sleep for 8 hours at a time. We don't need to "sleep each half of our brain" so we can keep breathing. Automating breathing isn't much different than automating swimming.Sharks don't breathe; they have no muscles that draw in water through their gills. The only way they can make that happen is by propelling their bodies through the water. If they stop moving they will suffocate.
Legend has it that the pirate Bluebeard was told that every one of his lined up men he ran past after they cut his head off would be spared. He ran towards the executioner and his sharp sword at the start of the line and saved 4 or 5 of his men, before ceasing to run / collapsing. I donít know if this is true, but it is plausible from what I do know.That could simply have been momentum carrying him forward, if he was running fast.
I have seen a movie of a brainless cat walking.Much of our memory is distributed throughout the nervous system rather than all of it resident in the brain. It's like the concept of a reflex center, only smaller. For example, you couldn't possibly play Chopin's Revolutionary Etude if you had to consciously think about every aspect of the motion of your fingers on the keyboard. A great deal of that is what we (imprecisely) call "muscle memory."

iceaura
03-01-11, 07:57 PM
There's a long and reasonably thorough (for its format) overview of the roles of the two halves of the vertebrate brain in Iain McGilchrist's book "The Master and His Emissary". The takehome is that the split is real but not simple, and has more to do with a fundamental difference in the kinds of attention necessary for handling the real world than some arbitrary division of processing tasks. (Shorthand: the left side focuses on specifics and parts, the right side forms coherent wholes and "big pictures", and this is so in vertebrates generally - many birds, for example, use their right eye to focus on seeds they are scarfing up, while watching the world for possibly dangerous anomalies in the big picture with their left eye).

One reason the seat of consciousness appears to be in the left brain is that in normal people that side suppresses the other during communication involving speech (McGilchrist has a theory that the left brain's increasing dominance in human social life is overreaching, and it's time that we learn to counter some of its effects). That the hemispheres actively suppress each other at times, in normal operations, can easily deceive observers about their underlying capabilities.

As McGilchrist observes (with many references throughout), damage to the right hemisphere is normally more debilitating and more difficult to recover from, despite the left hemisphere's apparent dominance and monopoly of speech, etc.

Fraggle Rocker
03-02-11, 04:36 PM
McGilchrist has a theory that the left brain's increasing dominance in human social life is overreaching, and it's time that we learn to counter some of its effects.Then he needs to smoke a lot more grass--or better yet, use one of the new (or old) smokeless delivery systems. Almost everyone I've known who used marijuana over the past four or five decades has reported that it seemed to suppress left-brain dominance. Computer programmers, lawyers, engineers, accountants, and the whole population of left-brained professionals looked forward to the occasional night off from relentless logical thinking, and used the time to paint, compose or play music, or engage in any number of creative activities. Musicians in particular (or perhaps simply because I'm a musician I had more elaborate conversations with them) said that they discovered and/or invented things while high that they had no trouble remembering and using when they came down.

This included simply thinking in the "coherent wholes and big pictures" that McGilchrist yearns for. I knew an attorney with an IQ of around 150 who always got high before going into court. He said it got him out of the linear, hierarchical thought patterns that bedevil most of us in the MENSA IQ range, so he could holistically challenge the opposition's entire case instead of focusing on one point at a time.

All of these people said that they felt that the drug simply knocked about 20 points off of their IQ, giving the other parts of their brain a chance to be heard. Of course they rigorously avoided recommending it to people of average intellect, having seen a few cases of them acting really stupid--these are undoubtedly the cases that the anti-marijuana nannies trumpet in the press. And of course people who are already stupid shouldn't even get close to it: they'll forget how toilets, toasters and traffic signals work, so their potential artistry will never be seen.