We generally experience ourselves as one person. There is an 'I' that thinks, feels, remembers, makes decisions and directs our actions. We rarely question this sense of unity.
But what if the human brain is not quite as unified as we imagine?
Some extraordinary experiments in neuroscience have challenged our understanding of what it means to be a single, conscious individual.
Two hemispheres, two different worlds?
The human brain has two hemispheres: the left and the right. They are connected by a thick bundle of nerve fibres called the corpus callosum, which allows information to pass between them.
For certain patients suffering from severe epilepsy, surgeons have sometimes severed this connection to prevent seizures from spreading from one hemisphere to the other. These patients became known as split-brain patients.
The documentary Your Brain: Who's in Control? presents some fascinating experiments involving these individuals.
In one experiment, a patient was asked to draw two different shapes simultaneously, one with each hand. In an individual with an intact corpus callosum, the two hemispheres communicate and coordinate their movements. In a split-brain patient, the hands could appear to compete, with each hemisphere directing its own hand independently.
Even more remarkable were experiments involving vision.
Information from the left visual field is primarily processed by the right hemisphere, while information from the right visual field is primarily processed by the left hemisphere. In most people, language production is predominantly associated with the left hemisphere.
Researchers briefly flashed the word TEXAS in the patient's left visual field. The right hemisphere registered the word, but the patient's speaking hemisphere could not report having seen it. However, when asked to draw something associated with the word, the patient used his left hand to draw a cowboy hat!
The right hemisphere had understood the information, even though the speaking hemisphere could not explain what had happened.
It was as if one part of the brain knew something that another part did not.
What does this tell us about the self?
Neuroscientist Michael Gazzaniga and his colleagues pioneered much of this research. Their work revealed that the brain contains multiple specialised systems capable of processing information and performing functions independently.
The findings raise a profound question: if different parts of our brain can process information independently, how does our experience of being one unified person emerge?
Importantly, this does not mean that everyone has two separate personalities or that the left and right hemispheres are two independent people. Nor should we confuse specialised brain functions with the popular idea that some people are 'left-brained' and others 'right-brained'. The actual science is considerably more nuanced.
Indeed, later research has shown that the separation is not absolute. Some forms of integration and coordinated behaviour remain possible even after the corpus callosum is severed. The nature of consciousness in split-brain patients continues to be debated.
An intriguing philosophical connection
This brings us to a question that Advaita Vedanta has explored from a very different standpoint.
We ordinarily identify ourselves with the body, thoughts, memories and personality. We assume that all these changing experiences belong to one unchanging 'I'.
But who is this 'I'?
The Mandukya Upanishad and its traditional Advaita interpretation invite us to enquire into the nature of the Self, rather than simply accepting the body-mind complex as our ultimate identity.
Neuroscience does not establish the Vedantic understanding of Atman. They are different enquiries, using different methods. Nevertheless, the split-brain experiments offer an interesting opportunity to question our unquestioned assumptions about the unity of the individual mind.
Perhaps what we experience as a single, unified personality is the outcome of numerous processes working together.
The more we understand the complexity of the mind, the more interesting the question of who we really are becomes.
A question to carry forward
If our thoughts, emotions and decisions are influenced by multiple processes within the brain, what determines the choices we ultimately make?
And what role do our emotions play in governing those choices?
In Part 3: Who Governs Your Emotions?
References and further reading
- Primary inspiration: NOVA/PBS, Your Brain: Who's in Control? — documentary.
- Gazzaniga, M. S. (2005). Forty-five years of split-brain research and still going strong. Nature Reviews Neuroscience, 6, 653–659. Read research review.
- de Haan, E. H. F. et al. (2020). Split-Brain: What We Know Now and Why This is Important for Understanding Consciousness. Neuropsychology Review, 30, 224–233. Read research review.
- Miller, M. B. et al. (2025). Split-brain patients: A clinical vs experimental perspective. Handbook of Clinical Neurology. Read research review.
- Mandukya Upanishad, with traditional Advaita interpretation.