I have recently been watching a BBC series called ‘Incredible Medicine: Dr Weston’s Casebook’, which tells astonishing stories of people with extraordinary lives. All of the people documented were amazing but there was one woman that particularly stunned me. It was the case study of Jody Miller; a woman who lives a perfectly normal and happy life with the absence of the entire left hemisphere of her brain.
From birth Jody suffered from Rasmussen’s Encephalitis, a rare neurological disorder characterised by unilateral (one sided) inflammation of the cerebral cortex. This caused drug-resistant epilepsy and cognitive degradation. Jody had frequent life-threatening seizures originating from the right side of her brain causing her to collapse to the left, reaching the point of having seizures every three minutes. For 2 years Jody’s parents tried different therapies but when every known treatment failed, the last resort was hemispherectomy, a procedure where half of the brain is surgically removed. Although unsure about the success of the outcome of the procedure, surgeons removed the right half of Jody’s brain in an attempt to alleviate her seizures.
Remarkably, the surgery was a complete success with the only issue being slight paralysis of the left side of her body that was resolved with astonishing speed through physiotherapy. The area left vacated by the right hemisphere was filled with cerebral fluid and the left hemisphere adopted the roles of its other half allowing Jody to lead an effectively normal life.
Jody’s was not the first hemispherectomy and certainly not the last; however, Jody’s was probably the most successful and this can be credited to neuroplasticity (also called brain plasticity). Neuroplasticity is how the brain reorganises itself by discarding some neural pathways and making other new ones. Nerve cells or neurons communicate via a cascade of electrical events. Electric signals travel along the axons of nerve cells from the dendrites, to the axon terminals and then cross the synapse (converted to chemical neurotransmitters here) to reach the postsynaptic neuron. Connections between neurons that constantly communicate with each other strengthen with time to form neural networks. So, when a person experiences the same thing repeatedly, stronger connections are formed and the signal can be transmitted quicker. This can be due to many things such as the dendrite end of a neuron growing more connection points and is also how memorising works.
The brain has a genetic blueprint to follow during development and this template has the potential to learn anything. Ultimately, however, it is the information flooding in that shapes the brain; this is called adaptive plasticity. Adaptive plasticity is thought to be most effective in toddlers as this is when the brain develops fastest. Two year olds have twice as many synapses in the brain than adults. By adolescence most of these synapses will have been pruned away leaving the most utilised neural pathways intact whilst having cut away the unimportant ones. This is how we forget, our brain physically loses the connections. Although this seems wasteful, the loss and the formation of synapses is driven by the need of neurons to maintain a certain electrical activity level. If the average electric activity falls below a certain threshold, the neurons begin to change and actively build new contact points and cross links, which allow them to receive signals from neighbouring cells that are perhaps overused. It is essentially a form of homeostasis: the body recognises the level of stimulus and adapts accordingly, perhaps disposing of less-than-essential pathways to use energy more efficiently.
*side note on learning*
Learning is not the same as memorising. Learning something new is more complicated than strengthening knowledge that is already familiar. However, everything new learned is in some way related to something that is already known. For illustration, first learning to speak is possible because the blueprint means the brain has connections that are almost capable of language. The exposure to speech in English or Mandarin or Dhivehi etc. will cause certain neurons to strengthen, physically redirect or wither away eventually leading to language assimilation. As evidence, English speakers discriminate the “b” sound from the “p” sound by recognising the time of the start of the sound relative to the time the lips part; this is a phoneme (the smallest meaningful unit of speech sound) boundary. These boundaries reflect language experience. Young children can distinguish more phonemic boundaries than adults, but they lose their discriminatory powers when certain boundaries are not experienced in the prevalent spoken language. For instance, Native Japanese speakers do not differentiate “r” and “l” sounds as this ability is lost in childhood because it is not in the speech that they are exposed to. Also, proof for everything new learned is in some way related to something that is already known can be exemplified in how much more likely you are to remember a new english word than a new french word if your first language is English.
Returning to adaptive plasticity, this is the principle reason why Jody was such a success story. Suffering with Rasmussen’s Encephalitis as a toddler her right hemisphere became somewhat useless and, therefore, regarded by the body as unimportant. To compensate, as her brain developed the neural pathways not being used in the right hemisphere due to the disorder deteriorated and instead formed in the left hemisphere. Essentially Jody’s body had already undertaken a functional hemispherectomy before doctors undertook the anatomical one. As a result, when the right hemisphere was removed the left was already somewhat equipped with the neural pathways to make up for the loss. Usually for brain injury victims rehabilitation is long and hard because the process of the brain reprogramming to reform the lost connections is analogous to a baby first learning to speak as the neural pathways are barely there and need to be physically repurposed to facilitate the specific task.
Jody’s story, to me, was incredible. Now in her 30s Jody has a more than decent college degree and lives proficiently with her husband of 4 years.
Lastly, to think about, for you to have read this post and understood it neuroplasticity has occurred in your brain leaving it physically altered forever. In fact every new experience rewires the brain, so you will truly never be the same again.
Learning in Parallel 