AI And AR System Offers New Effective Treatment For Phantom Limb Pain

The advanced technology is being used to bring to life a novel theory that suggests the pain comes from neural circuits that have lost their purpose due to the limb's amputation.
Shelby Rogers

One of the most mysterious effects about having a limb amputated is what researchers call "phantom limb" or "ghost limbs." Patients with phantom limb claim to still feel the missing limb, even if it feels slightly smaller in size to them than the actual limb. 

Neuroscientists and medical engineers have been working for years to better understand and treat phantom limb, as it often affects the relationship amputees have with their prosthetic limb(s). 

Max Ortiz Catalan of Chalmers University of Technology in Sweden claims he has a new hypothesis that could help doctors better understand and treat the condition. Catalan's proposed treatment also involves machine learning and augmented reality. 

Treating the pain of an inexistent limb 

Catalan focused his research more specifically on phantom limb pain, in which the lost limb can still experience or cause severe pain in a patient. The condition, if frequent, can cause the patient incredible pain. It can even be too painful in the area for them to consider putting on a prosthetic device. 

Catalan's proposed theory is that when a limb is amputated, the neural circuits that once had a purpose for the limb are left bare. They no longer serve a purpose and can get entangled with other neural networks. This leaves patients open to larger amounts of pain. 

"Imagine you lose your hand. That leaves a big chunk of 'real estate' in your brain, and in your nervous system as a whole, without a job. It stops processing any sensory input, it stops producing any motor output to move the hand. It goes idle -- but not silent," Catalan explained.

Neurons never stop functioning, Catalan said, and they can often fire at random. He noted that if neurons coincidentally fired together in the amputated area, it could lead to the perception of pain. 

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"Normally, sporadic synchronized firing wouldn't be a big deal, because it's just part of the background noise, and it won't stand out," continued Catalan. "But in patients with a missing limb, such event could stand out when little else is going on at the same time. This can result in a surprising, emotionally charged experience -- to feel pain in a part of the body you don't have. Such a remarkable sensation could reinforce a neural connection, make it stick out, and help establish an undesirable link."

Catalan noted that, while a lot of amputees experience phantom limb at some point, not all patients suffer from phantom pain. He said this is due to the fact that some patients might experience the simultaneous firing and thus linking while others never will. 

Could technology be the solution?

Catalan and his team suggest utilizing Phantom Motor Execution (PME) to treat the problem. During PME, patients have electrodes attached to the residual limb to pick up electrical signals meant for the missing limb. Through AI algorithms, those neurons become movements of a virtual limb on an AR or VR platform. If the patient sees themselves on a screen with a digital version of the limb, PME allows them to control the limb as they would normally. 

"The patients can start reusing those areas of the brain that had gone idle. Making use of that circuitry helps to weaken and disconnect the entanglement to the pain network. It's a kind of 'inverse Hebb's law' -- the more those neurons fire apart, the weaker their connection. Or, it can be used preventatively, to protect against the formation of those links in the first place," Catalan said.

The study was published in Frontiers in Neurology.

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