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NEW DELHI: Contrary to the widely held notion, the brain does not have the ability to rewire itself to compensate for the loss of sight, an amputation or stroke, for example, neuroscientists say.
They argue that the notion that the brain, in response to injury or deficit, can reorganise itself and repurpose particular regions for new functions, is fundamentally flawed, despite being commonly cited in scientific textbooks.
Instead, what is occurring in such scenarios is merely that one’s brain is being trained to utilise already existing but latent abilities, the researchers write in an article in the journal eLife.
“The idea that our brain has an amazing ability to rewire and reorganise itself is an appealing one. It gives us hope and fascination, especially when we hear extraordinary stories of blind individuals developing almost superhuman echolocation abilities, for example, or stroke survivors miraculously regaining motor abilities they thought they had lost,” writes John Krakauer, Director of the Center for the Study of Motor Learning and Brain Repair at Johns Hopkins University, US.
“This idea goes beyond simple adaptation or plasticity. It implies a wholesale repurposing of brain regions. But while these stories may well be true, the explanation of what is happening is, in fact, wrong,” writes Krakauer.
In their article, the neuroscientists look at ten seminal studies that purport to show the brain’s ability to reorganise.
One of these studies carried out in the 1980s at the University of California, San Francisco, looked at what happens when a hand loses a finger.
The hand has a particular representation in the brain, with each finger appearing to map onto a specific brain region, it said.
The study found that upon removing the forefinger in the hand, the area of the brain previously allocated to this finger was reallocated to processing signals from neighbouring fingers.
In other words, the brain has rewired itself in response to changes in sensory input.
The finding is disputed by the co-author of the eLife article, Tamar Makin, from the Medical Research Council (MRC) Cognition and Brain Sciences Unit at the University of Cambridge.
Makin offers an alternative explanation through her research.
In a study published in 2022, Makin used a nerve blocker to temporarily mimic the effect of amputation of the forefinger in her subjects.
She showed that even before amputation, signals from neighbouring fingers mapped onto the brain region ‘responsible’ for the forefinger.
In other words, while this brain region may have been primarily responsible for processing signals from the forefinger, it was not exclusively so.
All that happens following amputation is that existing signals from the other fingers are ‘dialled up’ in this brain region, Makin’s research found.
“The brain’s ability to adapt to injury isn’t about commandeering new brain regions for entirely different purposes. These regions don’t start processing entirely new types of information. Information about the other fingers was available in the examined brain area even before the amputation, it’s just that in the original studies, the researchers didn’t pay much notice to it because it was weaker than for the finger about to be amputated,” writes Makin in the article.
Understanding the true nature and limits of brain plasticity is crucial, both for setting realistic expectations for patients and for guiding clinical practitioners in their rehabilitative approaches, the scientists argue.
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