Our Brains Don’t Change Structure After Amputation

Research suggests our brains may not reconfigure as much as previously believed following an amputation.

The somatosensory cortex, which processes sensory data like touch and temperature from the entire body, has been shown in various studies to have distinct regions mapped to different body parts. For instance, the sensation of burning your hands might activate regions corresponding to your toes.

There is evidence indicating that when a nerve is severed, the somatosensory cortex may reorganize. A study observing macaques with severed arm nerves revealed that neurons typically responding to hand stimuli were instead active when the face was touched. The researchers inferred that some cortical areas initially linked to the hands were repurposed to respond to facial sensations.

However, a team led by Tamar Makin from Cambridge University conducted a groundbreaking comparison of brain activity in individuals before and after amputation, revealing minimal changes.

Using MRI, researchers scanned the brains of three participants prior to their medically necessary arm amputations. During the scans, they were instructed to pucker their lips and attempt to move their fingers.

Interestingly, even after numerous attempts to willfully move fingers they no longer possessed, the brain signals remained unchanged. “To the best of our measurement, they remain the same,” Makin noted.

Long-term follow-ups on two participants, 18 months and 5 years post-surgery, indicated no significant alterations in brain signals since the initial scans.

The researchers utilized an AI model that was trained to correlate brain activity with specific finger movements. When participants imagined moving their fingers in a random sequence, the model accurately identified which finger they were trying to move, demonstrating consistent neural activity.

In another experiment segment, somatosensory cortical activity was assessed in 26 individuals, average 23 years post-amputation, during attempts to move their lips and fingers. The findings showed comparable activity levels.

“This study decisively challenges the notion that the brain can easily remap, rewire, or reorganize as initially thought,” remarked John Krakauer from Johns Hopkins University in Maryland.

The implications of these findings could significantly affect treatments for phantom limb pain, a common condition where amputees experience discomfort in limbs that are no longer present.

Some therapeutic approaches utilize virtual reality and visual stimuli to prompt brain reorganization, yet results have varied, sometimes influenced by placebo effects, according to Makin.

Researchers suggest that innovative methods, such as implanting nerves into new tissues during amputation, might help mitigate this condition. If remaining nerves are left unconnected, they can thicken, potentially contributing to phantom limb pain.

“The previous maladaptive plasticity theory regarding phantom pain relied on the belief that reorganization was possible, which now seems incorrect,” stated Krakauer. “This fundamentally alters our approach to treating phantom limb pain since its underlying theory has been disproven.”