Split brains and functioning consciousness

I’ve written before about split-brain patients, those who, due to severe epilepsy, had the connections between the two hemispheres of their brain severed, yet were subsequently able to lead normal lives without themselves even noticing any cognitive change, which has profound implications for how consciousness works.

It turns out that there are people who are born with no connections between their brains, and one recently discovered patient still led a normal life: This Elderly Man Was Born With His Brain Hemispheres Disconnected. Did It Affect His Life? Hardly | Science Blogs | WIRED.

A new paper reports on an elderly gentleman, referred to as H.W., who aged 88 presented at a clinic complaining of recent intermittent problems controlling his left hand and some mild memory difficulties. Preliminary tests found him to be high functioning. He scored 30 out of 30 on the “mini mental state examination”, which is used to pick up signs of dementia or confusion. But when the researchers – a team led by Natalie Brescian – scanned H.W.’s brain, they made a surprising discovery. He had no corpus callosum. The main channel between his two brain hemispheres was completely missing.

The medical name for H.W.’s rare condition is agenesis of the corpus callosum, meaning that he was born with this structure missing. Given the importance of the callosum for connecting the bicameral brain, you’d think this would have had profound neuropsychological consequences for H.W. In fact, a detailed clinical interview revealed that he’d led a normal, independent life – first in the military and later as a flower delivery man. Until recently, he appeared to have suffered no significant psychological or neurological effects of his unusual brain. The problems with his left hand, H.W. said, were new.

When reading about split-brain patients, I always wondered if their ability to function might not have been reliant on functionality developed while their brain hemispheres were still connected.  In other words, whether it was possible for a segmented brain to function if it had always been segmented.

According to the article, many patients who are born congenitally this way are not high functioning, but this man’s story indicates that it is often possible.  In other words, our “self” can be split and still function as a unified self.  Which just further confirms that our brains are not a centrally controlled mechanism, but one with information processing and decision making distributed throughout its structure.

And consciousness is a central information gathering mechanism, one that gathers information in any way it can, including observing the self’s actions and concocting an explanation of its actions, even when it’s not privy to the actual information processing that led to those actions, as would be the case when the other half of a split brain initiated those actions.

This seems to indicate that consciousness is not in control.  The information it provides influences the brain’s actions, otherwise we couldn’t discuss it, but the initiation and execution of those actions appear to take place outside of consciousness.

Consciousness seems to function similar to how a city newspaper functions, gathering information about what is happening within the city and making its information available to the rest of the city, influencing what the city does, but not controlling it.

Until the newspaper reports on an activity, say a spike in crime, within the city, we could say that the activity is not yet in the city’s public consciousness.  Parts of the city may respond to the activity, but the city as a whole doesn’t yet know what is going on.  It is in the city’s collective subconscious.  Once the newspaper has reported, it is in the city’s collective consciousness, and affects what the parts of the city, the citizens, the police, the mayor, etc, do.

The newspaper gathers information in any way it can, including sometimes interpreting the public actions of portions of the city for which it may not have direct access to the inside story.  In my mind, that’s what the consciousness machinery in the brain of a split-brain patient is doing, and it’s why they can remain functional without themselves even noticing the difference.

10 thoughts on “Split brains and functioning consciousness

  1. My own take on it is that split-brain patients typically have two conscious minds. If both sides are used to the current state of affairs, then it will appear normal and they may have learned to work in concert with the other half without too much trouble, almost like the way that certain conjoined twins can learn to coordinate leg and hand movements so as to get around and tie shoelaces etc without too much difficulty. The difference is that split brain patients may not be aware there is another side.

    In a way, we may all be multi-minded. Many of the processes that happen in our brains are not conscious, or at least not directly accessible to the part of the mind that seems to have control over what we publicly say. But it is possible, as far as I can see, that some of these have their own distinct consciousness of which we are entirely unaware.

    Consciousness aside, it’s pretty remarkable that somebody can function normally without a corpus callosum, to the extent that they don’t notice a problem and nor does anybody else. It would seem that there is no way for information to get from one side of the brain to the other, but then it’s not clear how they can perform day to day tasks such as reading where each hemisphere processes half of the visual field. I would guess they have learned to make subtle adjustments to their behaviour in all kinds of ways to accommodate. It may be that they learn to let their eyes saccade around a scene a little differently to make sure both hemispheres get a chance to see everything. It’s also quite likely that the brain has developed a little differently, with perhaps more duplication of functionality on both sides of the brain to make sure both hemispheres can understand what’s going on well enough to work in tandem.

    I’d love to know more.


    1. From what I’ve read, the brain is not so much redundant between the hemisphere as it is symmetrical. The left hemisphere controls and receives signals from the right side of the body and the right hemisphere controls the left.

      You might be you’re right that each side has a consciousness. In the split-brain experiments, only the left side was articulative, which fits since Broca’s area, the language center, is on the left side. The right hemisphere could occasionally blurt out a word or two, but couldn’t do sentences. The problem is that if there is a consciousness on the right side, it can’t describe its existence.

      If there are two separate consciousnesses in split-brain patients, their ability to quickly be functional after their corpus callosum is cut seems to indicate that we all have those separate consciousnesses. But the one who does the talking about consciousness is the one on the left side.

      Your consideration of whether we all have several consciousnesses reminds me of speculation I once read about whether each body part has its own consciousness, and whether we should always use a local anesthetic when operating on, say, the hand, even if we’re already using use one that rendered the patient generally unconscious. Myself, I think consciousness requires a certain architecture (similar to the newspaper metaphor I described), so I tend to doubt that we have more than one or two.

      I learned a lot on this from Michael Gazzaniga’s book: ‘Who’s In Charge?’ and Michael Graziano’s ‘Consciousness and the Social Brain’. I highly recommend both books if you’re interested in doing a deep dive. Both are excellent writers.


  2. I would guess that a virtual corpus callosum is created by sensory inputs. Rather than the left side of your brain saying something, and the right side nearly instantly understanding what the left side is doing, it has to work its way out and vocalize, be heard by the right ear, and then the right brain goes, “Damn skippy! Preach, brother!” It’s not as fast or efficient, but the sharing of information is there. It’s just more like interpersonal communication rather than intrapersonal.


    1. You may be right. The thing is, given how fast split-brain patients recover, even those of us with functioning corpus callosums may be using interpersonal communication far more than we would have suspected.


  3. It is amazing that lacking such a seemingly crucial piece of anatomy, whether due to congenital defect or surgical intervention, doesn’t have obvious and hugely detrimental ramifications straight across the board. As WIRED author Christian Jarrett concludes, though, it is a testament to the adaptability of the human brain.

    On the feeling of a unified “self” for most regardless of the lack of cortical interhemispheric communication, Antonio Damasio proposes that much of the foundational work that goes into creating a “self” happens subcortically. That might render the state of the corpus collosum less critical for that specific process.

    And, in a fascinating chapter for:

    ‘Dual-Process Theories of the Social Mind’, Sherman, Gawronski, and Trope (editors) 2014

    … Roy Baumeister and John Bargh liken consciousness to an automotive GPS navigational system assisting the unconscious driver* on an as-needed basis:

    “The other compromise view, which both of us currently advocate, is that behavior is normally carried out by unconscious, automatic processes, while consciousness can occasionally intervene to override, regulate, redirect, and otherwise alter the stream of behavior – often at a distance, with unconscious processes filling in.”

    ‘Conscious and Unconscious: Toward an Integrative Understanding of Human Mental Life and Action’, Baumeister & Bargh 2014

    Click to access Baumeister%20&%20Bargh%20-%20Conscious%20and%20unconscious,%20toward%20an%20integrative%20understanding%20of%20human%20life%20and%20action.pdf

    * “unconscious driver” – not even going to go there 🙂


    1. I’ve seen other speculation that sub-cortical connections (presumably in the brain stem) might be making up for the cut corpus collosum. I think it’s pretty clear from the split-brain patient experiments that the cut does stop a lot of information transfer, but for the sense of self, I can definitely see it as a possibility. But if so, it means the sense of self is evolutionarily very ancient, dating to the earliest creatures with a brain, which seems like it would have interesting implications for the sentience of even the simplest animals.

      I’m starting to think that all of our actions are done outside the scope of consciousness, or at least awareness. Consciousness is sometimes aware of those actions afterward and confabulates a narrative of itself guiding things, or consciousness reports information to the sub-conscious, which then takes that information into account in its decisions, but the idea of consciousness actually pulling the strings in real-time is looking less and less plausible to me. Of course, the difference between causal influence and control could be considered a matter of semantics.

      LOLS, we need another term other than “unconscious” to discuss these things in a way that doesn’t invoke an image of a passed out driver riding their car off the road.


      1. On sentience – a good example of a trait differing in degree rather than kind across species as per Darwin.

        On “consciousness actually pulling the strings” – I’m leaning pretty hard the same way myself.

        I think it was in Bruce Hood’s ‘The Self Illusion’ that he described the feeling of thirst as notification of the brain’s decision to get up, go to the fridge, and get a drink(citing Daniel Wegner’s ‘The Illusion of Conscious Will’) only somewhat facetiously I think. The quote wasn’t in my notes – I just may have to reread the book.

        Liked by 1 person

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