Stable cortical body maps before and after arm amputation, 2025, Schone et al.

[SNT Gatchaman]

Stable cortical body maps before and after arm amputation

Spoiler: Authors

Schone, Hunter R; Maimon-Mor, Roni O; Kollamkulam, Mathew; Szymanska, Malgorzata A; Gerrand, Craig; Woollard, Alexander; Kang, Norbert V; Baker, Chris I; Makin, Tamar R

The adult brain’s capacity for cortical reorganization remains debated. Using longitudinal neuroimaging in three adults, followed before and up to 5 years after arm amputation, we compared cortical activity elicited by movement of the hand (before amputation) versus phantom hand (after amputation) and lips (before and after amputation). We observed stable cortical representations of both hand and lips in primary sensorimotor regions. By directly quantifying activity changes across amputation, we demonstrate that amputation does not trigger large-scale cortical reorganization.

Web | PDF | Nature Neuroscience | Open Access

 

[SNT Gatchaman]

Beyond the stability of lip representation across amputation, our findings reveal highly consistent hand activity despite amputation. This unchanged hand representation challenges the foundational assumption that S1 activity is primarily tied to its peripheral inputs, suggesting S1 is not a passive relay of its peripheral input, but an active supporter of a resilient ‘model’ of the body, even after amputation. Therefore, we conclude that, in the adult brain, S1 representation can be maintained by top-down (for example, efferent) inputs.

Our longitudinal approach reveals no signs of topographic reorganization in S1, not even subtle upregulation from homeostasis, further reinforcing the notion that S1 is not governed by deprivation-driven plasticity.

For phantom limb pain treatments, our study indicates that targeted muscle reinnervation and regenerative peripheral nerve interfaces do not ‘reverse’ reorganization or alter the cortical hand representation. Finally, our findings affirm the unaltered nature of adult sensory body maps after amputation, suggesting that Hebbian and homeostatic deprivation-driven plasticity is even more marginal than considered by even the field’s strongest opponents of large-scale reorganization.

 

[SNT Gatchaman]

Commentary in Nature: The brain’s map of the body is surprisingly stable — even after a limb is lost

Previous research had suggested that neurons in the brain region holding this internal map, called the primary somatosensory cortex, would grow into the neighbouring area of the cortex that previously sensed the limb.

But the latest findings, published in Nature Neuroscience on 21 August, reveal that the primary somatosensory cortex stays remarkably constant even years after arm amputation. The study refutes foundational knowledge in the field of neuroscience that losing a limb results in a drastic reorganization of this region, the authors say.

“Pretty much every neuroscientist has learnt through their textbook that the brain has the capacity for reorganization, and this is demonstrated through studies on amputees,” says study senior author Tamar Makin, a cognitive neuroscientist at the University of Cambridge, UK. But “textbooks can be wrong”, she adds. “We shouldn’t take anything for granted, especially when it comes to brain research.”

Study first author Hunter Schone, a neuroscientist at the University of Pittsburgh in Pennsylvania, says that previous reports from some people with amputations had led him and his colleagues to doubt the idea that the brain’s map of the body is reorganized after amputation. These maps are responsible for processing sensory information, such as touch or temperature, at specific body regions. “They would say: ‘I can still feel the limb, I can still move individual fingers of a hand I haven’t had for decades,’” Schone says.

To investigate this contradiction, the researchers followed three people who were due to undergo amputation of one of their arms. The team used functional magnetic resonance imaging (fMRI) to map the cortical representations of the body before the surgery, and then after the amputation for up to five years.

The analysis revealed that the brain’s representation of the body was consistent after the arm was amputated. Even five years after surgery, the cortical map of the missing hand was still activated in the same way as before amputation.

 

[Sean]

Count me among those unconvinced that the adult brain can reorganise to any major degree.

 

[Kitty]

Yeah, I'm not sure why this is surprising. There's no obvious survival advantage in remapping; rapid adaption to reduced or changed bodily function is much more important.

 

[Utsikt]

“Pretty much every neuroscientist has learnt through their textbook that the brain has the capacity for reorganization, and this is demonstrated through studies on amputees,” says study senior author Tamar Makin, a cognitive neuroscientist at the University of Cambridge, UK. But “textbooks can be wrong”, she adds. “We shouldn’t take anything for granted, especially when it comes to brain research.”

Maybe the problem is that those writing the textbooks don’t care about proofs, so opinions get presented like facts? Or they don’t understand the requirements of proofs and believe that flawed studies are sufficient?

This reminds me of high school level maths. We were never told that things were right because the teacher or textbook said so, we were shown that they were right through proofs.

How medicine keeps getting away with opinion based teachings is beyond me.