Max Ortiz-Catalan, PhD, Chalmers University of Technology, Gothenburg, Sweden, who conducts research using augmented reality to reduce phantom limb pain (PLP) in people with amputations, has developed a new theory and treatment for PLP that could lead to more effective treatment. Also advancing treatment of PLP, a new virtual reality (VR) tool is having success in initial studies in Brazil.

Ortiz-Catalan’s theory for the origin of PLP, called “stochastic entanglement,” builds upon his previous work that uses machine learning and augmented reality. He proposes that after an amputation, neural circuitry related to the missing limb loses its role and becomes susceptible to entanglement with other neural networks—in this case, the network responsible for pain perception.

“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,” he says. “It stops processing any sensory input; it stops producing any motor output to move the hand. It goes idle—but not silent.” He explains that when neurons are not processing a particular job, they may fire at random, which can result in coincidental firing of neurons in that part of the sensorimotor network, at the same time as from the network of pain perception. When they fire together, that creates the experience of pain in that part of the body.

Phantom Motor Execution

Ortiz-Catalan’s theory also explains why not all amputees suffer from PLP; the randomness, or stochasticity, means that simultaneous firing may not occur in all patients.

His new research also includes a novel treatment method for PLP that he developed, Phantom Motor Execution (PME). During PME treatment, electrodes attached to the patient’s residual limb pick up electrical signals intended for the missing limb, which are then translated through artificial intelligence algorithms into movements of a virtual limb in real time. The patients see themselves on a screen, with a digitally rendered limb in place of their missing one, and they can then control it as if it were their own biological limb. This allows the patient to stimulate and reactivate those dormant areas of the brain.

“The patients can start reusing those areas of brain that had gone idle. Making use of that circuitry helps to weaken and disconnect the entanglement to the pain network,” says Ortiz-Catalan, head of the university’s Biomechatronics and Neurorehabilitation Laboratory. It can also be used preventively before the undesirable links are formed. The PME treatment method has been shown to help patients for whom other therapies have failed. A device allowing for this treatment is being commercialized by Integrum AB, a Swedish medical device company, and an international clinical trial in seven countries is in progress that includes ongoing brain imaging studies.


Another tool intended to help treat PLP and make physical therapy and prosthetic training more engaging was released this month in the form of a new VR game by Accenture. The connected armband and application give physical therapists access to the data to create more personal therapy plans for patients and to see the electrical signals being produced by the patients’ muscles.

The application is being tested at the Hospital das Clinicas in São Paulo, Brazil. The initial findings suggest that patients are making greater improvements than just physical therapy alone, and physical therapists reported more accurate calibration of the patients’ prostheses.

“Our application takes intelligent technologies such as Internet of Things, analytics, and virtual reality to rapidly create an easy-to-use, cost-effective application,” Daniel Gonzalez, managing director for Accenture Brazil, told MobiHealthNews. After the testing in Brazil is complete, the application will be donated to hospitals and made available on multiple platforms.

To see a video presentation of Phantom Motor Execution in action, visit Phantom motor execution in Augmented Reality as a treatment of Phantom Limb Pain on YouTube.

To read Ortiz-Catalan’s paper, “The stochastic entanglement and phantom motor execution hypotheses: a theoretical framework for the origin and treatment of PLP,” visit Frontiers of Neurology.

Editor’s note: Part of this story was adapted from materials provided by Chalmers University of Technology.

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