By Endominance | February 2, 2020
If you were to split a brain in half – would your consciousness also be divided? What about the notion that some people are more right-brained and others more left-brained?
In the original findings of split-brain theory, researchers believe that patients who underwent surgery to sever the corpus callosum, the nerve tract connecting the two hemispheres of the brain, would also experience a split within their consciousness. They also hypothesized that the right and left hemispheres of the brain perform very different functions – or brain laterality. They believed that when the two sides of the brain weren’t able to communicate with each other, they responded differently to stimuli, indicating that the hemispheres have different functions. Are these claims true, just a myth, or somewhere in-between?
Split-brain theory has its place in the advancement of neuroscience. However, scientists are now challenging the theory, claiming there is no evidence of a divided consciousness in patients or that one side of the brain is universally dominant than the other. Additionally, researchers are looking at how our brain processes information coming from different streams of perception.
History Behind Split Brain Theory
The brain is fascinating and complex. Every inch of the mind controls certain functions of our body as well as processes information. When we look at the structure of the brain, we also notice that the brain is split into two sides or hemispheres, with the corpus callosum bridging these regions. As far back as the 1940’s, patients with severe cases of epilepsy sometimes underwent a procedure that split this connection to help relieve their symptoms. By cutting the corpus callosum (also known as a corpus callosotomy), it would also sever the transmission of epileptiform discharges, which caused seizures. As a result of this procedure, it also severed the ability to integrate the perception, recognition, and responding functions that take place between the two hemispheres of the brain. While patients were still able to have these functions, researchers soon began to theorize how each region of the brain operated independently from each other.
Sperry’s Work
According to Nobel laureate Dr. Roger W. Sperry, after a patient underwent this procedure, he or she seemed to experience a split in consciousness where the left and the right side of their brain could independently become aware of and respond to stimuli. To test his hypothesis, Sperry would have patients in an apparatus that split their fields of view. The left hemisphere perceives information coming from the right visual field, and the right hemisphere perceives from the left. Sperry tested visual material projected to the right half of the field/left-hemisphere system of a right-handed patient and found that speech and writing processes to be typical.
However, when the same visual material was projected onto the left half of the field, hence to the right hemisphere, the subject claimed they did not see anything, or that there was only a flash of light on the left side (Sperry, 1968). Sperry described the hemispheres as “two separate conscious entities or minds running in parallel in the same cranium, each with its own sensations, perceptions, cognitive processes.” Michael Gazzaniga, who worked under Sperry, went on to hypothesize the capacity of each hemisphere of the brain and insisted the vast majority of cases from split-brain surgical procedures reveal little cognitive ability in their right hemispheres. Sperry’s research opened up new frontiers in neuroscience and helped advance our knowledge of hemispheric specialization, cognition, and even human consciousness.
However, critics of Sperry’s research often debate two distinct issues within his hypothesis, including lateralization of brain function and the theory that once the two hemispheres of the brain are split, so is the consciousness.
Lateralization of Brain Functions
In terms of lateralization of brain functions, one critic, Dr. Michael Corballis, understood that there are areas in the brain for language and some for spatial functions. Still, Corballis felt that an individual was not just right-brained or left-brained or as he states, “These centers have to do with how the normal brain processes the world, and not with how people differ from each other. To say that the two hemispheres have somewhat different functions is not a myth. But it is wrong to say that one or the other side is universally dominant. Dominance is task-related, not person-related (Corballis, 2007).”
Corballis also points out that creativity is often considered a right-brain trait, and yet language, which is very creative, takes place in the left brain for most people – even most left-handed people whose hand skills are controlled by the right brain. “People do, of course, vary in analytic powers and emotionality. This doesn’t mean they fall into distinct groups. Both measures are continuous rather than discrete. For example, you can be both analytic and emotional (Corballis, 2017).”
Conscious Unity, Split Perception
A study from Yair Pinto, assistant professor of cognitive psychology at the University of Amsterdam, also challenges Sperry’s original work. Instead, Pinto proposes an alternative, the “conscious unity, split perception” model. For their study, Pinto and his fellow researchers carried out a series of tests on two patients who had undergone a full callosotomy. Pinto states, “Our aim was to determine whether the patients performed better when responding to the left visual field with their left hand instead of their right hand and vice versa (Pinto et al, 2017).” The classic view of this theory poses that a split-brain patient can report seeing a stimulus shown in the left visual field, but only with their left hand, not the right. An image in the right visual field can be reported with the right hand alone and also verbally; this is because language is located in the left hemisphere of the brain.
However, to the researchers’ amazement, the patients were able to respond to stimuli throughout the entire visual field normally, or more specifically, with all response types: left hand, right hand, and verbally. “The patients could accurately indicate whether an object was present in the left visual field and pinpoint its location, even when they responded with the right hand or verbally. This happened even though their cerebral hemispheres can hardly communicate with each other (Pinto et al, 2017).” Patients also reported:
- Being able to see their entire visual field
- Having feeling and control of their entire body
- Conscious unity was unchanged since the operation
Pinto concluded that even without communication between the cerebral hemispheres – there was no evidence of a split consciousness in the patients.
New Frontiers
Both, traditional and contemporary research into split-brain theory has its own inherent value in advancing the study of the human brain. With the new research, we now see that the activity of the left hemisphere is not a local perception activity, but a higher level of perception, which can pick up details beyond the obvious. Left/right or split-brain theory cannot be pigeon-holed into the lateralization of brain function or the division of consciousness. Rather, it is how our brain processes information coming from different streams of perception – eventually leading individuals to understand and integrate perceived information and respond behaviorally.
References
Corballis, M. C. (2007). The dual-brain myth. Tall Tales about the Mind and Brain Separating Fact from Fiction, 291–313. doi: 10.1093/acprof:oso/9780198568773.003.0019
Pinto, Y., Haan, E. H. D., & Lamme, V. A. (2017). The Split-Brain Phenomenon Revisited: A Single Conscious Agent with Split Perception. Trends in Cognitive Sciences, 21(11), 835–851. doi: 10.1016/j.tics.2017.09.003
Sperry, R. W. (1968). Hemisphere disconnection and unity in conscious awareness. American Psychologist, 23(10), 723–733. doi: 10.1037/h0026839