The spinal cord can learn and remember independently of the brain

Spinal cord research at the RIKEN Center for Brain Science (CBS) in Japan, led by Aya Takeoka, has unveiled revolutionary insights into its capabilities, demonstrating its potential for independent motor learning and memory.

The experts have identified two key groups of neurons within the spinal cord: one essential for acquiring new motor skills, and another for retrieving these learned skills.

Spinal capabilities

Traditionally, it was believed that the spinal cord’s role in motor control was merely reactionary, dependent on the brain’s commands. However, evidence from nature, such as headless insects that can still adapt their leg movements, hinted at a more autonomous function.

Until now, the mechanisms behind such phenomena remained a mystery. “Gaining insights into the underlying mechanism is essential if we want to understand the foundations of movement automaticity in healthy people and use this knowledge to improve recovery after spinal cord injury,” explained Takeoka.

Mice learn leg movements via spinal cord

To delve deeper into this autonomous capability, Takeoka’s team devised an innovative experiment using mice. They created conditions where a mouse’s spinal cord could learn and recall leg movements without brain input.

In their setup, mice were subjected to electrical stimulation based on the position of their hindlegs. Notably, if a mouse’s leg drooped, it triggered a stimulation, simulating an adverse event that the animal would naturally want to avoid.

Lasting spinal learning

The results were striking. After only ten minutes of this setup, the experimental mice adjusted their leg positions to avoid stimulation. This behavior demonstrates a clear example of motor learning occurring directly at the spinal level.

Moreover, this learning was not fleeting. A day later, the same mice retained their adjusted leg positions, even when roles were reversed with control mice.

Mapping memory and learning

Further exploration into the neural circuitry responsible for these capabilities used transgenic mice with specific spinal neuron populations disabled.

Subsequently, the team made an important discovery: disabling neurons at the top of the spinal cord, particularly those expressing the gene Ptf1a, hindered the mice’s ability to adapt their movements. As a result, the mice could not effectively avoid electrical shocks.

Conversely, neurons in the lower, ventral part of the spinal cord, which express the En1 gene, proved crucial for this learning process.

Silencing these neurons a day after the initial adaptation had a significant effect. It rendered the spinal cord unable to recall the learned avoidance, effectively erasing the ‘memory’.

In a significant finding, stimulating these En1-expressing neurons during the recall phase had a dramatic effect. The stimulation not only brought back the learned behavior but also enhanced the response speed by 80 percent. This indicates an amplified recall ability.

A paradigm shift in motor learning

These groundbreaking findings challenge the traditional view that motor learning and memory are exclusively brain-centric.

“Not only do these results challenge the prevailing notion that motor learning and memory are solely confined to brain circuits, but we showed that we could manipulate spinal cord motor recall, which has implications for therapies designed to improve recovery after spinal cord damage,” said Takeoka.

The study reshapes our understanding of the spinal cord’s role in motor function. Additionally, it opens new avenues for rehabilitation strategies following spinal injuries, offering hope for enhanced recovery and autonomy in affected individuals.

Potential applications of spinal cord in motor learning

Using the spinal cord for learning, particularly in the context of motor functions, is an exciting area of neuroscience that can have significant implications for rehabilitation and enhancing motor abilities. Here’s how we can harness the spinal cord’s learning capabilities:

Rehabilitation after spinal injuries

Understanding that the spinal cord can independently learn and remember motor tasks opens up innovative approaches for rehabilitation after spinal cord injuries.

Tailored rehabilitation programs that engage spinal motor learning can help patients regain motor functions. These might involve repetitive, task-specific exercises that encourage the spinal cord to “relearn” movements even if some brain-to-spinal cord pathways are damaged.

Enhancing neural plasticity

Treatments could focus on enhancing neural plasticity within the spinal cord. This might include pharmacological approaches that promote the growth and strengthening of neural connections or neurotrophic factors that support neuron health and growth.

Electrical stimulation therapies, such as transcutaneous electrical nerve stimulation (TENS) or spinal cord stimulation (SCS), can also be used to facilitate this learning process.

Prosthetic integration

Advanced prosthetics could be developed to integrate directly with the spinal cord’s neuronal circuits, allowing users to control these devices through the spinal cord’s intrinsic learning capabilities.

This approach could provide more intuitive control of prosthetics, as the spinal cord could potentially learn and adapt to the prosthetic as if it were a natural part of the body.

Adaptive sports training

For athletes, especially those adapting to changes in mobility or those using assistive devices, training programs could be designed to maximize the spinal cord’s motor learning capabilities.

Such training would optimize the spinal cord’s ability to coordinate complex movements that are specific to different sports, enhancing performance and movement efficiency.

Neurofeedback and biofeedback

Techniques that provide real-time feedback on spinal cord activity could be used to train individuals to modify their spinal cord responses for better motor control.

This can be particularly useful in teaching new locomotor skills or in recovery scenarios where traditional brain-focused methods are less effective.

Research involving spinal cord and motor learning

Continuing to research the spinal cord’s learning capabilities could lead to new models of motor function and disorder. These models can further refine our understanding and treatment of various conditions affecting motor control, from paralysis to muscular dystrophy.

By leveraging the spinal cord’s ability to learn and adapt independently of the brain, we can develop more effective therapeutic strategies and technologies that improve mobility, enhance performance, and offer new hope to individuals with motor impairments.

The study is published in the journal Science.

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