Brains at the Brink - Split-Brain Consciousness
Does slicing the brain in half create two minds? Exploring the wild worlds of the split brain.
Epilepsy can be a strange thing. Essentially what happens during a major epileptic seizure is that a burst of signal ripples throughout the entire brain, bouncing from one hemisphere to the other. Imagine basically every single part of the brain all activating all at once. The motor cortex lights up like a Christmas tree and activates muscles you wouldn't even know you had. Thankfully, like an explosion, its effect is only temporary, and eventually the seizure fizzles out, returning the brain to something like normality.
When the seizures become too frequent, too disruptive, too resistant to all other treatment: medical intervention steps in. The scalpel is the last line of defence. In a procedure as drastic as it is effective, the corpus callosum - the bundle of neural fibres that bridges the two hemispheres - is severed. It’s akin to cutting the main telephone line in an office building; suddenly, the left and right hemispheres find themselves isolated, each unaware of the other's activities. The intention is to prevent the storm of electrical activity from spreading, to confine the seismic commotion to one hemisphere.
It does come with one small side-effect: A peculiar condition commonly known as Split Brain Syndrome. Like a house divided, the left and right hemispheres, in their newfound separateness, begin to reveal the unique competencies and quirks that had been masked by their previously harmonious collaboration.
On the outside, there's an eerie sense of normalcy - speech, mobility, and routine functions remain largely unaffected. However, delve deeper and you'll find a mind that's anything but ordinary. In the most intriguing of scenarios, the left hemisphere - the seat of our linguistic abilities - might decide to pick up a book and read, while the right hemisphere - silent, yet intensely perceptive - might simultaneously reach for a cup of coffee. In this strange dance of dual consciousness, each hemisphere seems to harbour its own will, its own desires, orchestrating actions unbeknownst to the other. The person is left, quite literally, with one hand unaware of what the other is doing. The harmony has been disrupted, and in its place, an uncanny duet unfolds.
In this fascinating world of split-brain individuals, the brain begins to operate like two separate entities cohabiting in the same skull; and in fact, that's exactly it. Two separate and distinct subjective and conscious experiences, unaware of the other, and yet both attempting to continue on like the sole inhabitant of the body.
Note from the Author: I’m so sorry for not having posted in so long. It turns out I might very well have bipolar of some type, and so when I’m in a depressive episode, everything just stops. It also makes returning to those things afterward a challenge, because of my anxiety of letting people down. Regardless, I’m so glad you’re here, on this journey with me. None of this would happen if it wasn’t for you. Each and every subscriber just lifts my spirits and makes all of this possible. Thank you.
Diving deeper
The left hemisphere, often dubbed the 'dominant' side in the majority of right-handed individuals, takes charge of the linguistic and logical aspects of our cognition. It's the talkative twin in this cranial duo, responsible for speech production, comprehension, reading, and writing. However, its capabilities stretch beyond the realms of language and logic; it's also associated with number skills, reasoning, and analytical thought. In a split-brain person, these functions remain largely intact. They can still articulate their thoughts, engage in conversation, solve mathematical problems, and make logical decisions, all thanks to the diligent workings of the left hemisphere. But here’s the catch: while it's adept at these complex tasks, it's only privy to the sensory input from the right half of the world. As a result, split-brain individuals might find themselves articulating thoughts and feelings driven solely by their right-side perceptions, manifesting a cognitive asymmetry as intriguing as it is surreal.
Yes, that means when you are talking with a split-brain individual, it is their left-hemisphere that responds, producing the words that are emitted from their mouths. Remarkably, however, both hemispheres can hear you speak, and while the left has more powerful language comprehension abilities, the right is not completely in the dark here. It can still process some of this itself, and will sometimes have its own distinct reactions to what it has heard, with the two sides occasionally being in total disagreement or conflict.
Across the great divide, the right hemisphere, seemingly shrouded in silent shadow cast by its loquacious counterpart, reveals its own unique prowess. Spatial awareness, facial recognition, and visual imagery are in its domain. It's also adept at perceiving emotional nuances, interpreting tone, and reading non-verbal cues. Without the mastery of the spoken word, it makes its presence felt through actions. In split-brain individuals, the right hemisphere can respond independently to stimuli presented to the left field of vision or the left side of the body. It might laugh at a joke only it understands, or react emotionally to a scene only it sees. The right hemisphere is perceiving the world entirely independently, painting its own vivid picture of reality, distinct from the logical narratives spun by the left. This divergence, this literal duality of mind, brings to light the fascinating complexity of the human brain in ways we are still striving to understand.
You know when a friend laughs at your joke, but then says "I don't get it"? In split-brain individuals, the laughter is a response from the right hemisphere, and the follow-on statement is coming from the left. If you then ask the individual if they thought the joke was funny, you might even get "no" as a response, despite all body language to the contrary!
However, try asking this individual why they laughed, and you might get something utterly incoherent.
The weird stuff
One of the most well-known experiments conducted by Michael Gazzaniga - arguably one of the godfathers of split-brain research - involved a patient known as "Joe". In this experiment, Gazzaniga showed Joe two images simultaneously, with each image presented to one visual field and thus processed by the opposite hemisphere. For instance, an image of a chicken claw was shown to Joe's right visual field (and thus processed by the left hemisphere), while an image of a snowy scene was shown to his left visual field (right hemisphere). When asked to choose from an array of pictures related to what he just saw, Joe's right hand (left hemisphere) pointed to a chicken, while his left hand (right hemisphere) pointed to a shovel (to clear the snow). When asked why he chose these images, Joe, with his speech controlled by the left hemisphere, could only explain choosing the chicken, not the shovel.
This experiment revealed that the two hemispheres could process different information and make independent decisions, but only the left hemisphere, which controls speech, could articulate a reason for its choice. The right hemisphere, on the other hand, made a perfectly logical decision (the shovel for the snow) but couldn't verbalise its choice. This supported Gazzaniga's theory of the "left-brain interpreter" - the idea that the left hemisphere has a special role in creating narratives and explanations for our thoughts and actions.
In another experiment, Gazzaniga presented the word "KeyRing" to a split-brain patient, with "Key" projected to the left visual field (right hemisphere) and "Ring" to the right visual field (left hemisphere). When asked to say what they saw, the patient responded "Ring," as speech production is a left-hemisphere function. However, when asked to point to what they saw using their left hand (controlled by the right hemisphere), they pointed to a key.
Ohhh it gets weirder
Here is a morality tale. Is it permissible to attempt to poison someone even if the attempt fails? “Permissible” in the moral sense here, not legal or any other sense. Is it morally acceptable to attempt to cause someone harm and/or death if the attempt fails? The answer is obvious. That is, unless you’re the left hemisphere.
The spontaneous drive to interpret and rationalise events in the world is a well-known phenomenon in split-brain research (Gazzaniga, 2000), as is the rationalisation of moral judgments in the general population (Haidt, 2001). In this study, it appears the patients sensed their judgments were not quite right, and they often offered rationalisations for why they judged the act as they did without any prompting. For example, in one scenario a waitress served sesame seeds to a customer while falsely believing that the seeds would cause a harmful allergic reaction. Patient J.W. judged the waitress’s action as "permissible." After a few moments, he spontaneously offered, "Sesame seeds are tiny little things. They don’t hurt nobody," as though this justified his judgment.
- Abnormal moral reasoning in complete and partial callosotomy patients (M.B. Miller et al, 2010)
Hold on a second. When I asked you before whether you would see it as “permissible” or not, did you feel any need to justify your answer? Your inner monologue certainly spoke your answer, you heard it. I heard it. (Not really, but I know you thought it). Did it follow up with the reasons why? Did it feel like it needed to?
Clearly it’s morally forbidden to attempt to deliberately cause someone serious injury or death, regardless of the actual outcome. This one is a no-brainer (so to speak), for those of us with a connected right hemisphere. We don’t even need to explain why. It might as well be an axiom. However, for some reason, we see here that when the right hemisphere is disconnected, and the left brain is forced to give its answer alone, no matter how confident it might be in its choice, something doesn’t feel quite right. When we don’t feel quite right about something like this, the urge to explain, interpret, contextualise and rationalise can become overpowering, almost automatic. No one asked, but the left brain decided that there had to be a *reason* for it answering “yes this is permissible”. Sesame seeds, that’s it! Who could be hurt by a sesame seed? They’re tiny, therefore totally harmless.
???
If you feel like that doesn’t make sense, you’re not wrong. It doesn’t make sense, it’s a weird and disjointed idea, and does not have relevance to the fact that this is an allergic reaction scenario, not a “ballistic sesame-seeds” scenario. That’s a great question for Myth Busters: can sesame seeds cause damage if used as a high velocity projectile?
The left brain is filling in gaps here, that much we can see. Michael Gazzaniga, in his book The Consciousness Instinct, explores why that might be. I highly recommend giving it a read, it is absolutely fascinating end-to-end.
Subjective Experience
We are the product of our physical brain. That’s where consciousness comes from. Removing parts of the brain that provide certain aspects of our consciousness removes those things from our conscious experience. There is so much more I could write here about this, but I think that’s enough for one day. It’s clear that splitting the brain - assuming the now-separate pieces remain alive and functioning - also splits consciousness into two distinct entities. Remember, it’s all just chemistry!