What Split-Brain Patients Reveal About the Architecture of Consciousness and the Self

What if you saw something that only your brain perceives, while being unable to verbally express it to others? While it sounds impossible, it can happen for some patients whose brain hemispheres have been surgically disconnected.

For context, the human brain can be primarily distinguished by the left and right hemispheres. They are connected by the corpus callosum, a bridge made of a massive network of nerve fibers that allows the hemispheres to exchange information (de Haan et al., 2020). You may have heard of the “logical left brain” or the “creative right brain”, but these misconceptions often oversimplify their specialized functions. The left hemisphere is typically dominant for language, while the right hemisphere plays an important role in spatial processing with both sides controlling the opposite side of the body.

This division becomes remarkable when their keystone, the corpus callosum, is severed. Now, it’s no joke to mess with the brain, and it wasn’t an easy decision for researchers to conduct this procedure. However, patients with severe epilepsy, a series of repeated, unprovoked seizures, weren’t left with many treatment options. Following the procedure, common symptoms for epilepsy like uncontrolled muscle jerks or loss of consciousness were significantly relieved. However, it’s concurrently been observed that information could become trapped on one side of the brain (Pinto et al., 2023). The treatment opens up an investigation for how the brain will function as a whole with the two hemispheres unable to communicate with each other.

Consider the famous experiment conducted by pioneering researchers in neuropsychology, Michael Gazzaniga and Roger Sperry. Split brain patients were presented with the image of a chicken claw to their right visual fields and a snowy scene to the left visual field. The brain processes information from the right side into the left hemisphere of the brain, and vice versa (Purves et al., 2001). When asked to select images with matching descriptions to what they saw, the patient’s right hand chose a chicken, while the left hand chose a shovel (Marinsek et al., 2014). In a way, both the left and right hemisphere correctly identified with their corresponding stimuli. But in regards to the brain as a whole, was there a right or wrong to the body’s differing response?

Under the circumstance that the brain attempts to function independently per hemisphere, one might wonder if that will ever lead to a struggle for dominance in the self’s consciousness. A strange phenomenon showed that the left appears to act as an “interpreter,” constructing explanations for actions even when it lacks the information that initially caused them. To create a coherent story, the brain may sometimes implement false information that explains why we acted after the fact (Marinsek et al., 2014). It’s hard to imagine living with memories that never existed yet contribute to a person’s identity.

So what does this mean for the origin of consciousness and how the “self” should be defined?

Perception, language, emotion, memory, and decision making emerge from constant communication and negotiation between specialized systems. The feeling of being one continuous “I” could be understood as the product of their successful cooperation. The most unsettling discovery learned from split-brain patients is not that one brain can potentially become two minds, but that we may never have been as unified as we imagined.

Science cannot tell us for certain whether split-brain patients truly experience two consciousnesses, but ongoing research suggests that some abilities remain integrated even after the hemispheres are disconnected (de Haan et al., 2020). What’s so mind blowing is how much of these processes occur without putting our consciousness to make them happen. Who knows how many more natural processes are firing behind the scenes without us acknowledging them?

If consciousness can be fragmented while the feeling of “self” remains, then perhaps the self is less like a single voice and more like an harmonizing orchestra.

References

• de Haan, Edward H F et al. “Split-Brain: What We Know Now and Why This is Important for Understanding Consciousness.” Neuropsychology review vol. 30,2 (2020): 224-233. doi:10.1007/s11065-020-09439-3
• Pinto, Yair et al. “Visual integration across fixation: automatic processes are split but conscious processes remain unified in the split-brain.” Frontiers in human neuroscience vol. 17 1278025. 10 Nov. 2023, doi:10.3389/fnhum.2023.1278025
• Marinsek, Nicole et al. “Divergent hemispheric reasoning strategies: reducing uncertainty versus resolving inconsistency.” Frontiers in human neuroscience vol. 8 839. 21 Oct. 2014, doi:10.3389/fnhum.2014.00839
• Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. A Dramatic Confirmation of Language Lateralization. Available from: https://www.ncbi.nlm.nih.gov/books/NBK11085/