Reevaluating Brain Capabilities: New Insights Challenge Conventional Notions of Neural Plasticity

Recent studies by Professors Tamar Makin and John Krakauer have cast doubt on the long-standing belief that the brain can adapt by rewiring itself in response to sensory deficits such as blindness or stroke effects. Their analysis of key studies indicates that the brain does not develop new functions in unrelated areas. Instead, it enhances existing capabilities through practice and learning. This finding is vital for setting realistic rehabilitation goals and understanding the efforts involved in recovery narratives.

Contrary to common assumptions, the brain lacks the ability to reconfigure itself to make up for losses like blindness, amputations, or stroke-related impairments, as per researchers from the University of Cambridge and Johns Hopkins University.

In a paper published in eLife, Professors Tamar Makin (Cambridge) and John Krakauer (Johns Hopkins) argue that the popular idea of the brain repurposing specific regions for new tasks following injury or deficit is incorrect, even though this concept is frequently cited in scientific literature. They suggest that the brain is instead training itself to better use its inherent, but previously underutilized, capabilities.

Misunderstandings About Brain Flexibility

A commonly cited example is the supposed rewiring of the visual cortex in blind individuals to process sound, enabling them to navigate using a form of ‘echolocation.’ Similarly, it’s often believed that stroke victims who initially can’t move their limbs learn to use other brain areas to regain control.

Krakauer, the head of the Center for the Study of Motor Learning and Brain Repair at Johns Hopkins University, noted that the idea of the brain’s remarkable adaptability is enticing, offering hope and intrigue. This is especially true when considering exceptional cases of blind people developing extraordinary echolocation skills or stroke survivors regaining lost motor functions.

“This notion extends beyond mere adaptation or plasticity – it implies a complete repurposing of brain regions. However, while these stories are inspiring, the explanation for them has been misinterpreted,” he said.

Reexamining Influential Studies

Makin and Krakauer reviewed ten influential studies that claimed to demonstrate the brain’s capacity for reorganization. They concluded that while these studies do show the brain’s adaptability, they do not support the creation of new functions in unrelated areas. Instead, they reveal the brain’s use of pre-existing, latent capabilities.

For instance, a study by Professor Michael Merzenich at the University of California, San Francisco, in the 1980s examined the brain’s response when a finger is lost. Merzenich argued that the brain area previously linked to the lost finger gets reassigned to neighboring fingers, suggesting brain rewiring. Makin, however, offers a different interpretation based on her research.

Questioning the Rewiring Concept

In a 2022 study, Makin simulated the effect of amputating a forefinger using a nerve blocker. She found that signals from neighboring fingers were already connected to the brain region responsible for the forefinger, indicating that this area was not exclusively for the forefinger. Following amputation, the existing signals from other fingers are simply emphasized more in this region.

Makin, from the Medical Research Council (MRC) Cognition and Brain Sciences Unit at the University of Cambridge, stated: “The brain’s adaptability in response to injury doesn’t involve commandeering new brain areas for different purposes. These regions don’t start processing entirely new types of information. The information about other fingers existed in the brain area even before amputation, but it was not the primary focus in earlier studies.”

Evidence from Studies on Deaf Cats

Another example challenging the reorganization theory comes from research on congenitally deaf cats. In these cats, the auditory cortex, which normally processes sound, seemed to be adapted for vision. However, once fitted with cochlear implants, this area promptly reverted to processing sound, suggesting no permanent rewiring had occurred.

Reviewing additional studies, Makin and Krakauer found no conclusive evidence that the visual cortex in congenitally blind individuals or the unaffected cortex in stroke survivors developed new functional abilities.

Comprehending Real Brain Adaptability

Makin and Krakauer do not disregard the accomplishments of blind individuals in navigating using hearing or stroke patients regaining motor functions. They propose that rather than completely repurposing regions for new tasks, the brain is enhancing or modifying its existing structure through practice and learning.

This understanding of the brain’s true nature and limitations of plasticity is critical for setting realistic expectations for patients and guiding clinical practitioners in rehabilitation methods.

Makin emphasized: “The learning process reflects the brain’s remarkable, yet limited, capacity for adaptability. There are no quick fixes in this journey. The notion of rapidly accessing untapped brain potentials is more a wishful thought than a reality. Progress is slow and incremental, requiring continuous effort and practice. Recognizing this fact is important for appreciating the hard work behind every recovery story and for adjusting our strategies accordingly.

“Often, the brain’s adaptability has been portrayed as

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• New Insights into Brain Plasticity
• Brain Adaptation and Sensory Deficits
• Rethinking Brain Plasticity and Rehabilitation
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• Exploring the Limits of Brain Plasticity