Skulls full of electricity
We’re not always aware of it, but there is a 3-pound sack of flesh sitting in our heads, responsible for every thought and action, all of the time. Those 3 pounds are full of activity — neurons firing electrical impulses from end to end, helping everything from our conscious thoughts and unconscious reflexes manifest.
You might not think about it, but you’re awfully lucky to have those 3 pounds in there. There’s a lot we know brains can do, but still so much more that we don’t yet know about. Damage to even small chunks weighing close to half a gram could have devastating consequences.
Now imagine you had only half a brain…
Such is the case of Christina Paravecchia. In 1996, Paravecchia underwent a medical procedure known as a hemispherectomy to remove the entire right hemisphere of her brain. Paravecchia suffered from a condition that caused her to have around 150 seizures a day, incapacitating her nearly completely. To treat her condition, Dr. Ben Carson removed her right brain, leaving her with only half the organ we hold so dear.
They said she would never be able to walk, drive, or work a normal job. She was fated to live an unsatisfactory life. She was 8 years old at the time.
Today, Christina Paravecchia is a married mother of two, holds a Master’s Degree in Speech Pathology, and currently works as a speech pathologist. She is partially paralyzed on one side of her body but has learned to do most basic tasks with her one functional arm. The brain doesn’t regrow, as the liver might. To this day, she lives with half a brain.
“There is probably some voodoo going on here”, you say. There’s no way you can do all these things with half a brain. Taking care of two children is mentally taxing on most people with a whole brain! How can we live — let alone, scale such great heights — with only half of that mysterious lump of cells in our skulls?
It used to be thought that brains cannot regrow themselves; however, more recent scientific discoveries have revealed that the brain is more plastic than was previously known. In the early days of studying the brain as an organ, most scientists thought function was fixed throughout adulthood. Not only that, even during childhood most important areas of the brain were understood to have specific functions that they were being trained to do. Damage to one area would not likely be compensated for by other areas. Clearly, this cannot be true — the case of Paravecchia is a glaring counterexample.
And she is not the only one. There have been many patients who have had hemispherectomies, though the procedure is becoming less common as more sophisticated and less invasive procedures are being developed to treat the same disorders. One such patient is reported to have regained “above normal” language capacity and superior intellectual capacity despite undergoing a left-brain removal at the age of 5.1 This is particularly shocking because the left brain is largely responsible for language processing and acquisition, so to undergo removal of the left brain and develop superior language ability is beyond impressive. The average person struggles to do this with the left side of their brain intact.
One might argue that this healing only occurs for a child. Their brains are not developed enough to have set functions. To a large extent, hemispherectomies and other procedures that remove large areas of the brain are reserved for children (for reasons we will go into more detail on). But this is not a hard and fast rule. Many case studies have shown that a number of adult hemispherectomy patients have gone on to live fulfilling lives, far surpassing expectations. This substantial healing is even possible for patients who have smaller regions of their brain affected and do not undergo hemispherectomy at all. Dr. Norman Doidge’s books The Brain that Changes Itself and The Brain’s Way of Healing provide countless other instances of these fascinating healing stories.
The answer lies in a phenomenon first discussed in 1890 by William James, an American psychologist. James introduced the idea of “plasticity” in behavior, the idea that behaviors were moldable and shapeable. The idea led to James proclaiming that the brain was not a fixed entity with a definite pattern of behaviors and functions. This idea was, to a large extent, rejected by the broader scientific community. Other scientists would also propose the idea of brain plasticity or neuroplasticity, but it was only in the latter part of the 1900s that the idea gained more traction in the neurological community.
Neuroplasticity is a newer idea in neuroscience and there is still much to learn, however, we do have a decent understanding of what it entails. In essence, it is the principle that the brain is not fixed; rather, it is capable of adapting itself to meet certain needs throughout the course of one’s life. Neurons can make new connections in such a way that the wiring of the brain is remapped to direct certain functions to new regions. In fact, in periods of critical neuroplasticity (usually in childhood and early development), certain brain functions that are lost in one area could be almost entirely commandeered by other regions of the brain. This serves to explain how individuals like Christina Paravecchia were able to accomplish many functions with only half a brain — likely, due to their young age, the remaining hemisphere they had was able to remap its connections and regain many lost functions.
As we mentioned, plasticity is not limited to children. Though invasive procedures like hemispherectomy are not recommended for adults since plasticity begins to weaken over time, there are many cases where lost brain functions can be regained by other areas.
Such is the case in many stroke victims who are paralyzed on one side of their body. Following their stroke, these individuals can train their brains to write with their non-dominant hand (if their dominant side is paralyzed) and perform many functions with the unparalyzed half of their body). It is clear that various brain circuits can be rewired to avoid damaged areas while retaining as much function as possible — how the brain does this is mostly an open question in neuroscience and neurobiology.
So, where does that bring us? Can we one day train brains to entirely rewire themselves following a traumatic brain injury? At present, it is not possible to know exactly how much neuroplastic regrowth and remapping can or will occur following an injury. In extreme cases, the hope is that the brain will be able to remap itself, however, it goes without saying more extensive treatments will be necessary for the more severe cases.
What can be said, however, is that the world of neuroplasticity potentially holds a wealth of new insights on neurorehabilitation, the process of recovering from brain and nervous system damage.
2. Doidge, Norman. The Brain’s Way of Healing (Updated Edition): Remarkable Discoveries and Recoveries from the Frontiers of Neuroplasticity. Scribe, 2017.
This article was written by Sameer Rajesh, who is a sophomore undergraduate student at UC Berkeley studying Molecular and Cellular Biology, and Michael Xiong, who is a sophomore undergraduate student at UC Berkeley studying Chemical Biology. This article was edited by Oliver Krentzman, a senior undergraduate student at UC Berkeley studying Cognitive Science, and Abraham Niu, a junior undergraduate at UC Berkeley studying Cognitive Science and Data Science.