Your Brain Cannot Rewire Itself, New Study Argues

Researchers from the University of Cambridge and Johns Hopkins University argue that the brain does not have the ability to rewire itself to compensate for loss of sight, amputation, or stroke.

Professors Tamar Makin (Cambridge) and John Krakauer (Johns Hopkins) argue in eLife that the notion that the brain can reorganize itself and repurpose specific regions for new functions in response to injury or deficit is fundamentally flawed, despite being widely cited in scientific textbooks. Instead, they contend that what is happening is simply the brain getting trained to employ previously existing but buried abilities.

“The idea that our brain has an amazing ability to rewire and reorganize 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’d lost. 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,”

said Krakauer, Director of the Center for the Study of Motor Learning and Brain Repair at Johns Hopkins University.

Latent Capacities, Not New Ones

In their article, Makin and Krakauer look at 10 seminal studies that purport to show the brain’s ability to reorganize.

One of the most prominent examples offered is when a person loses their sight, or is born blind, and the visual cortex, which was previously specialized in processing vision, is rewired to interpret noises, allowing the individual to use a type of ‘echolocation’ to traverse a chaotic space. Another common scenario is persons who have had a stroke and are unable to move their limbs at first, utilizing other sections of the brain to regain control.

The new study’s authors argue, however, that while the studies do indeed show the brain’s ability to adapt to change, it is not creating new functions in previously unrelated areas; instead it’s using latent capacities that have been present since birth.

Remapping Fingers?

One of the studies, for example, looked at what happens when a hand loses a finger. It was conducted in the 1980s by Professor Michael Merzenich at the University of California, San Francisco.

Each finger appears to map into a specific brain region in the brain’s image of the hand. Merzenich argued that removing the forefinger reallocates the portion of the brain previously assigned to this finger to processing information from nearby fingers. In other words, the brain has rewired itself in response to changes in sensory input.

Not so, says Makin, whose own research provides an alternative explanation.

Dialing Up Other Inputs

Makin used a nerve blocker in a 2022 study to temporarily mimic the effect of forefinger amputation in her subjects.

She demonstrated that, even before amputation, impulses from nearby fingers mapped onto the brain region responsible for the forefinger — that is, while this brain region was largely responsible for processing signals from the forefinger, it was not solely responsible. Following amputation, existing impulses from the other fingers are ‘dialed up’ in this brain region.

“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,”

Makin, from the Medical Research Council (MRC) Cognition and Brain Sciences Unit at the University of Cambridge, said.

Enhancement and Modification

Another striking counterexample to the reorganization argument can be found in a study of congenitally deaf cats, in which the auditory cortex (the part of the brain that processes sound) appears to have been repurposed to process vision. However, when they are equipped with a cochlear implant, this brain region immediately resumes processing sound, indicating that the brain had not been rewired.

Examining other studies, Makin and Krakauer found no compelling evidence that the visual cortex of individuals who were born blind or the uninjured cortex of stroke survivors ever developed a novel functional ability that did not otherwise exist.

Makin and Krakauer do not disregard reports of blind people being able to navigate solely by hearing, or stroke patients regaining motor functions, for example. Instead of entirely repurposing regions for new activities, they propose that the brain enhances or modifies its pre-existing architecture through repetition and learning.

The Brain’s Remarkable Capacity for Plasticity

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, they argue.

“This learning process is a testament to the brain’s remarkable — but constrained – capacity for plasticity. There are no shortcuts or fast tracks in this journey. The idea of quickly unlocking hidden brain potentials or tapping into vast unused reserves is more wishful thinking than reality. It’s a slow, incremental journey, demanding persistent effort and practice. Recognizing this helps us appreciate the hard work behind every story of recovery and adapt our strategies accordingly. So many times, the brain’s ability to rewire has been described as ‘miraculous’—but we’re scientists, we don’t believe in magic. These amazing behaviors that we see are rooted in hard work, repetition and training, not the magical reassignment of the brain’s resources,”

Makin added.

Abstract

Neurological insults, such as congenital blindness, deafness, amputation, and stroke, often result in surprising and impressive behavioural changes. Cortical reorganisation, which refers to preserved brain tissue taking on a new functional role, is often invoked to account for these behavioural changes. Here, we revisit many of the classical animal and patient cortical remapping studies that spawned this notion of reorganisation. We highlight empirical, methodological, and conceptual problems that call this notion into doubt. We argue that appeal to the idea of reorganisation is attributable in part to the way that cortical maps are empirically derived. Specifically, cortical maps are often defined based on oversimplified assumptions of ‘winner-takes-all’, which in turn leads to an erroneous interpretation of what it means when these maps appear to change. Conceptually, remapping is interpreted as a circuit receiving novel input and processing it in a way unrelated to its original function. This implies that neurons are either pluripotent enough to change what they are tuned to or that a circuit can change what it computes. Instead of reorganisation, we argue that remapping is more likely to occur due to potentiation of pre-existing architecture that already has the requisite representational and computational capacity pre-injury. This architecture can be facilitated via Hebbian and homeostatic plasticity mechanisms. Crucially, our revised framework proposes that opportunities for functional change are constrained throughout the lifespan by the underlying structural ‘blueprint’. At no period, including early in development, does the cortex offer structural opportunities for functional pluripotency. We conclude that reorganisation as a distinct form of cortical plasticity, ubiquitously evoked with words such as ‘take-over’’ and ‘rewiring’, does not exist.

Reference:

1. Tamar R Makin, John W Krakauer (2023). Against cortical reorganisation. eLife 12:e84716