The Man Who Lived Without 90% of His Brain

To ensure confidentiality, the patient described in this study is referred to as 'Patient W.H.', a pseudonym used in place of his real name. 

 

How much of your brain do you actually need to function normally? A 44-year-old French civil servant and father of two, referred to as Patient W.H., managed to lead an ordinary life—despite having lost more than 90% of his brain tissue. Could this astonishing case finally prove the long-debated myth that humans use only 10% of their brains? This medical miracle has profoundly challenged our core understanding of consciousness, cognition and brain plasticity.  

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Can Humans Function With 10% of Their Brain? 

Patient W.H., a seemingly healthy man, decided to visit the hospital after experiencing two weeks of mild weakness in his left leg. What began as a routine check-up took a shocking turn–brain scans revealed that the majority of his brain was missing. Inside his skull, only a thin outer layer of the cerebral cortex remained, with the rest of the space filled by fluid.  

 

This condition, known as hydrocephalus—commonly referred to as “water on the brain”—occurs when excess cerebrospinal fluid (CSF) accumulates within the brain’s ventricles (Fig. 1). These fluid-filled cavities play a crucial role in cushioning the brain and removing metabolic waste. Hydrocephalus affects approximately 0.3 to 2.5 per 1,000 live births, making it nearly as common as Down syndrome in new-borns. 

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Fig.1: A comparison of a normal brain and one with hydrocephalus. In hydrocephalus, excess CSF leads to increased pressure, enlarging the ventricles and compressing the surrounding brain tissue. (Source: KidsHealth.org (2019)).

 

When CSF fails to drain properly, the ventricles expand, exerting pressure on surrounding brain structures. One of the most affected areas is the periventricular white matter, a dense network of nerve fibers (axons) around the ventricles. As the ventricles enlarge, they compress these fibres and initiate a cascade of events that lead to nerve damage, impairing effective communication between brain structures. These structural changes typically lead to motor and cognitive impairments, including coordination problems, headaches, vision disturbances, sleep disorders, and memory or concentration difficulties. 

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Patient W.H. had been diagnosed with hydrocephalus at six months old and received a ventriculoatrial (VA) shunt, a device designed to drain excess CSF from the brain’s ventricles to the atrium of the heart, relieving pressure in the brain. However, at the age of 14, he developed ataxia (loss of coordination) and paralysis in his left leg, which resolved after a shunt revision. Shortly after, the shunt was removed entirely, causing CSF to build up over the next 30 years, progressively enlarging his ventricles and eroding much of his brain’s internal structures (Fig. 2). 

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Fig. 2: Brain scans of Patient W.H. with chronic hydrocephalus. The large black spaces indicate extensive replacement of brain tissue by cerebrospinal fluid (CSF). A: CT scan showing enlarged lateral ventricles (LV). B, C, D: MRI scans revealing enlargement of the lateral (LV), third (III), and fourth (IV) ventricles, compressing the cerebral cortex into a thin layer against the skull. (Source: Feuillet, Dufour, & Pelletier (2007).) 

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Despite Patient W.H.’s severe anatomical abnormalities, his neurological development and medical history remained remarkably intact. Cognitive assessments revealed an IQ of 75, with a verbal IQ of 84 and a performance IQ of 70—scores only slightly below the average.  

 

Similarly, another hydrocephalus case involved a mathematics student with an IQ of 126, whose brain also consisted of just a thin layer of cerebral cortex covering massively enlarged ventricles. Despite the drastic damage, his intellectual abilities remained well above average. Successive research has found no direct correlation between ventricular enlargement and IQ scores in hydrocephalus patients, suggesting that the brain’s ability to function may not strictly depend on its physical volume. 

 

Whilst these findings highlight how extraordinary the human brain truly is, they also challenge seminal hypotheses about the brain's functionality. Unique cases like these could open doors to new and exciting research directions into neuroplasticity and the anatomical and cellular basis of cognition and consciousness. 

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Our Brains are More Adaptable Than We Ever Thought  

Brain scans (Fig. 2) reveal that the minimal neural structures necessary for Patient W.H. to retain cognitive abilities and consciousness were the upper layers of the cerebral cortex and the brainstem. These two abilities are among the most fundamental aspects of human function: cognition refers to mental processes such as memory, reasoning, and problem-solving, while consciousness is the awareness of oneself and the surrounding world. If Patient W.H. could function normally while missing 90% of his brain, how are cognition and consciousness truly distributed? And what does this reveal about the minimum brain tissue required to sustain them? 

 

Current theories suggest that cognition and consciousness arise from a network of specific brain regions (Fig. 3). Consciousness, for example, is typically associated with structures including the brainstem, Ascending Reticular Activating System (ARAS), thalamus, cerebral cortex, and basal forebrain, with damage to any of these areas potentially impairing conscious awareness. However, cases such as the patient with a near-empty brain contradict this model, suggesting that other factors may contribute to consciousness, underpinning the complexity of the human brain.

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​Fig. 3: Current understanding of brain regions responsible for functions that contribute to cognition and consciousness. (Source: HappyNeuron Pro (n.d.).) 

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One possible explanation lies in Cleermans’ “Thesis of Radical Plasticity”, which proposes that consciousness is not innate but learned. According to this hypothesis, the brain constantly adjusts, refining its functions and develops self-awareness through experience—essentially forming a "theory of itself". This adaptability enables different brain regions to learn consciousness and compensate for structural deficits. Patient W.H.’s case of chronic hydrocephalus exemplifies this, as the slow progression of brain loss over decades provided sufficient time for neural reorganisation, preserving function despite extreme tissue reduction. 

 

The “Radical Plasticity Thesis” is evident in various conditions other than hydrocephalus. After a stroke, for instance, the brain works to regain lost abilities by strengthening existing connections between nerve cells (synaptic plasticity) and reassigning tasks to different brain areas (cortical remapping) to restore motor and cognitive functions. Similarly, following limb amputation, the brain undergoes cortical remapping that results in the sensation of a "phantom limb”, where individuals continue to perceive the presence of the missing limb. 

 

Even in healthy individuals, extensive training has been shown to induce neural plasticity. Indeed, a well-known study on London taxi drivers revealed that those who underwent spatial navigation training developed a larger posterior hippocampus compared to the others. This structural expansion is believed to reflect the increased demands placed on their spatial memory—a clear example of experience-driven neuroplasticity. These findings provide evidence of the brain’s ability to adapt structurally and functionally in response to injuries, malformations or environmental stimuli (Fig. 4).  

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Fig. 4: The two main forms of neuroplasticity are structural and functional plasticity. Structural neuroplasticity involves the physical remodelling of brain tissue in response to learning, experience or environmental changes. Functional neuroplasticity refers to the process by which surviving neurons reorganise and form new connections following injury or disease to preserve function. (Source: Ramasubramanian, 2022.) 

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Therapeutic Potential of Neuroplasticity 

Studying brain plasticity, particularly through cases like hydrocephalus, provides insights into clinical applications. If the brain can rewire itself so dramatically, could we harness this ability for recovery and cognitive enhancement? 

 

Early intervention programs focusing on motor development to leverage plasticity have been effective in facilitating normal developmental trajectories in children with hydrocephalus. Even when developmental delays occur, cognitive rehabilitation therapies such as targeted cognitive exercises may be implemented to strengthen neural networks and address learning and memory deficits, underscoring the therapeutic potential of modulating neuroplasticity.  

 

Furthermore, the principles of neuroplasticity have also been applied in the development of non-invasive brain stimulation techniques to treat neurological and psychiatric disorders. For example, Transcranial Direct Current Stimulation (tDCS) involves delivering a low electrical current to the scalp to modulate neural activity and promote plasticity in targeted brain regions. Indeed, tDCS is currently being investigated for its potential to enhance cognition in conditions like depression, anxiety, and post-stroke motor deficits, presenting a novel non-pharmacological approach for treating CNS disorders. 

 

Perspectives 

Beyond hydrocephalus, research into neuroplasticity has revolutionised our understanding of the brain, resulting in the development of a range of recovery and cognitive enhancement methods, from stroke rehabilitation to brain stimulation technologies. 

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Yet, many questions remain. If a near-empty brain can sustain consciousness and cognitive function, how much of the brain is truly "necessary"? And could future technologies unlock even greater adaptive potential? If we can enhance the brain for "perfection," where do we draw the line? As our understanding of neuroplasticity advances, it may not only reshape medicine and cognition but also challenges the very definition of consciousness itself. 

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References  

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Boly, M., Massimini, M., Tsuchiya, N., Postle, B. R., Koch, C., & Tononi, G. (2017). Are the neural correlates of consciousness in the front or in the back of the cerebral cortex? Clinical and neuroimaging evidence. The Journal of Neuroscience, 37(40), 9603–9613. https://doi.org/10.1523/jneurosci.3218-16.2017 

Cleeremans, A. (2011). The radical plasticity thesis: How the brain learns to be conscious. Frontiers in Psychology, 2. https://doi.org/10.3389/fpsyg.2011.00086 

Dennis, M., Spiegler, B.J., Simic, N., Sinopoli, K.J., Wilkinson, A., Yeates, K.O., Taylor, H.G., Bigler, E.D. and Fletcher, J.M. (2014). Functional Plasticity in Childhood Brain Disorders: When, What, How, and Whom to Assess. Neuropsychology Review, 24(4), 389–408. https://doi.org/10.1007/s11065-014-9261-x. 

EMOTIV. (n.d.). Neuroplasticity. EMOTIV Blog. Retrieved from https://www.emotiv.com/blogs/glossary/neuroplasticity 

Feuillet, L., Dufour, H., & Pelletier, J. (2007). Brain of a white-collar worker. The Lancet, 370(9583), 262. https://doi.org/10.1016/s0140-6736(07)61127-1 

Flanders, T. M., Billinghurst, L., Flibotte, J., & Heuer, G. G. (2018). Neonatal Hydrocephalus. NeoReviews, 19(8), e467–e477. https://doi.org/10.1542/neo.19-8-e467 

Goldfine, A.M. and Schiff, N.D. (2011). Consciousness: Its Neurobiology and the Major Classes of Impairment. Neurologic Clinics, 29(4), 723–737. https://doi.org/10.1016/j.ncl.2011.08.001. 

HappyNeuron Pro. (n.d.). What are Cognitive Functions? HappyNeuron Pro. Retrieved from https://www.happyneuronpro.com/en/info/cognitive-functions/ 

Hochstetler, A., Raskin, J. and Blazer-Yost, B.L. (2022). Hydrocephalus: historical analysis and considerations for treatment. European Journal of Medical Research, 27(1), 168. https://doi.org/10.1186/s40001-022-00798-6 

Hydrocephalus Association. (2020). Hydrocephalus in infants and children: Diagnosis & treatment. Hydrocephalus Association. Retrieved from https://www.hydroassoc.org/hydrocephalus-in-infants-and-children/ 

MacIver, K., Lloyd, D.M., Kelly, S., Roberts, N. and Nurmikko, T. (2008). Phantom limb pain, cortical reorganization and the therapeutic effect of mental imagery. Brain, 131(8), 2181–2191. https://doi.org/10.1093/brain/awn124. 

Murphy, T.H. and Corbett, D. (2009). Plasticity during stroke recovery: From synapse to behaviour. Nature Reviews Neuroscience, 10(12), 861–872. https://doi.org/10.1038/nrn2735 

New Scientist. (2007). Man with tiny brain shocks doctors. New Scientist. Retrieved from https://www.newscientist.com/article/dn12301-man-with-tiny-brain-shocks-doctors/ 

Nitsche, M. A., & Paulus, W. (2011). Transcranial direct current stimulation – update 2011. Restorative Neurology and Neuroscience, 29(6), 463–492. https://doi.org/10.3233/rnn-2011-0618 

Oliveira, G. R., & Fabris Vidal, M. (2020). A normal motor development in congenital hydrocephalus after Cuevas Medek Exercises as early intervention: A case report. Clinical Case Reports, 8(7), 1226–1229. https://doi.org/10.1002/ccr3.2860 

Olopade, F., Shokunbi, M., & Sirén, A.-L. (2012). The relationship between ventricular dilatation, neuropathological, and neurobehavioral changes in hydrocephalic rats. Fluids and Barriers of the CNS, 9(1), 19. https://doi.org/10.1186/2045-8118-9-19 

Ramasubramanian, L. (2022). Neuroplasticity. UC Davis Biotechnology Program. Retrieved from https://biotech.ucdavis.edu/blog/neuroplasticity 

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