The brain is a highly resilient organ containing about 86 billion neurons in a human adult brain and a similar number in newborns. However, infants have many more synaptic connections that continue to develop after birth. Due to the abundance of neuronal capacity, especially in children, pruning (the elimination of weak synapses) is necessary to strengthen frequently used brain pathways and hinder the growth of weak neural connections. Most people assume losing half of the brain would make normal life impossible. Yet every year, a small number of children undergo a hemispherectomy, a surgery that removes or disconnects one cerebral hemisphere, and many eventually learn to walk, speak, and attend school. How is this possible?
What Happens During a Hemispherectomy
A hemispherectomy is an operation that disconnects the diseased tissue from the healthy hemisphere (functional) or completely removes a hemisphere of a child’s brain (anatomic). Although the surgery is mostly used for extreme seizures that can’t be treated with medication, it can also be the treatment for abnormal findings found on MRIs (Magnetic Resonance Imaging) or other conditions. This type of treatment is one of the rarest forms of brain surgery, with less than 100 children receiving it per year in the United States.
Image courtesy of Hemispherectomy – Pediatric Neurosurgery | UCLA Health
Losing part or half of your brain can sound unimaginable or even drastic, but it connects to the brain’s deep history of neuron resilience and strong ability to adapt, especially during early childhood. This is why most hemispherectomies are performed and successful on children. During early childhood, your brain isn’t fully pruned, causing it to have an excess of synapse connections than adulthood, which is referred to as plasticity ( being able to form new connections). The science behind neuroplasticity is what allows for surgeries similar to this to be able to work.
Understanding the Importance of Neuroplasticity
Neuroplasticity refers to the brain’s ability to reorganize and modify its neural connections in response to stimuli, experience, learning, etc. It plays a crucial role in developing and maintaining brain function as well as recovering from injury and changes within the environment you’re in. This is extremely important when discussing a surgery such as a hemispherectomy, as it is your brain and body’s only gateway in rehabilitating itself. Functional and structural neuroplasticity are necessary for recovery of brain processing and normal psychological components of a normal life.
Functional neuroplasticity is focused on memory formation, acquiring skills, and recovering from injuries. Long-term Potentiation (LTP) is a commonly used example of functional plasticity, where it consists of strengthening your synapse through repeated stimulation. This can be seen through everyday activities such as understanding concepts for a subject or test through repeated studying and review. Due to the fact that the developing brain is highly plastic, children are better able to reorganize existing neural circuits after a hemispherectomy than adults. Due to a lack of neuronal pathways and connections, young children are unable to fully develop strong synapses for memory, speech, or walking. This answers the question of why it is harder to remember life during early childhood, such as your first word or learning how to walk.
Image courtesy of Neuron | Definition, Structure, Types, & Functions | Britannica
Structural neuroplasticity refers to physical changes to neural circuits such as the growth of dendritic spines, axonal sprouting, and neurogenesis ( growth of new neurons). This is essential to recovery from brain injury, neurodevelopment, and adaptations to sensory input alterations. White matter contains bundles of nerve fibers that transmit signals between brain regions, while gray matter contains the cell bodies responsible for processing information. After a hemispherectomy, your brain suffers from damaged tracts within white matter as gray matter goes through adaptations, and network-level connectivity shifts. Rather than replacing the lost hemisphere with large numbers of new neurons, the remaining hemisphere reorganizes existing neural circuits; surviving networks assume functions once shared by both hemispheres. New connections begin to form through the other hemisphere of the brain, and axons begin to sprout. Ultimately, this forces the brain to slowly adapt to sending signals only to one half of the brain, leaving the other side behind.
The hemispherectomy procedure demonstrates one of neuroscience’s most remarkable discoveries which is that the developing brain is far more adaptable than scientists once believed. Although losing an entire hemisphere is life-changing, neuroplasticity allows many children to regain abilities that once seemed impossible. Continued research into this extraordinary recovery may improve treatments for epilepsy, traumatic brain injury, and other neurological disorders.
Works Cited
Professional, Cleveland Clinic Medical. “Hemispherectomy.” Cleveland Clinic, 26 Dec. 2025, my.clevelandclinic.org/health/procedures/17092-hemispherectomy.
Kim, Ju-Seong, et al. “Hemispherotomy and Functional Hemispherectomy: Indications and Outcomes.” Journal of Epilepsy Research, vol. 8, no. 1, June 2018, pp. 1–5, doi:10.14581/jer.18001.
Websiteadmin. “Hemispherectomy for Epilepsy: A Guide to Surgery and Recovery.” Pediatric Epilepsy Surgery Alliance, 17 Feb. 2026, epilepsysurgeryalliance.org/about/surgery-info/hemispherectomy-surgeries-epilepsy.
Grey, Heather. “What Can Happen When You Remove Half a Brain to Cure Epilepsy.” Healthline, 26 Nov. 2019, http://www.healthline.com/health-news/heres-what-happens-when-you-remove-half-your-brain.
“Hemispherectomy.” UCLA Health, http://www.uclahealth.org/medical-services/pediatric-neurosurgery/conditions-treatment/pediatric-epilepsy-surgery/epilepsy-treatment/hemispherectomy.
Marzola, Patrícia, et al. “Exploring the Role of Neuroplasticity in Development, Aging, and Neurodegeneration.” Brain Sciences, vol. 13, no. 12, Nov. 2023, p. 1610, doi:10.3390/brainsci13121610.
About the Author
Hi! My name is Fiona Washington, and I am a rising junior in high school from Towson, Maryland. I’m passionate about neuroscience and cognitive processes; my dream is to one day become a neuroscientist and contribute to a scientific breakthrough such as a cure to neurodegenerative diseases. I love encouraging young women pursuing STEM and making more opportunities for us to be seen.
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