By Restoring Sense of Touch to Amputees, HAPTIX Seeks to Overcome Physical and Psychological Effects of Upper Limb Loss

To understand the meaning of “proprioception,” try a simple experiment. Close your eyes and lift your right arm above your head. Then, move it down so that it’s parallel to the ground. Make a fist and release it. Move it forward, and then swing it around behind you like you’re stretching. Finally, freeze in place, open your eyes, and look. Is your arm positioned where you thought it would be?

For most people, the answer will be, “Yes.” That’s because your brain and nervous system worked together to move your body according to your intent and processed the sensory feedback to know where your arm was in space despite not being able to visually track it.

For many upper-limb amputees using prosthetic devices, the answer would be, “No.” They wouldn’t have confidence that their device would be where they think it is because current prostheses lack provisions for providing complex tactile and proprioceptive feedback to the user. Without this feedback, even the most advanced prosthetic limbs will remain numb to the user and manipulation functions will be impaired.

DARPA’s new Hand Proprioception and Touch Interfaces (HAPTIX) program seeks to deliver those kinds of naturalistic sensations to amputees, and in the process, enable intuitive, dexterous control of advanced prosthetic devices that substitute for amputated limbs, provide the psychological benefit of improving prosthesis “embodiment,” and reduce phantom limb pain. The program builds on neural-interface technologies advanced during DARPA’s Revolutionizing Prosthetics and Reliable Neural-Interface Technology (RE-NET) programs that made major steps forward in providing a direct and powerful link between user intent and prosthesis control.

HAPTIX aims to achieve its goals by developing interface systems that measure and decode motor signals recorded in peripheral nerves and/or muscles. The program will adapt one of the advanced prosthetic limb systems developed under Revolutionizing Prosthetics to incorporate sensors that provide tactile and proprioceptive feedback to the user, delivered through patterned stimulation of sensory pathways in the peripheral nerve. One of the key challenges will be to identify stimulation patterning strategies that elicit naturalistic sensations of touch and movement. The ultimate goal is to create a fully-implantable device that is safe, reliable, effective, and approved for human use.

“Peripheral nerves are information-rich and readily accessible targets for interfacing with the human nervous system. Research performed under DARPA’s RE-NET program and elsewhere showed that these nerves maintain motor and sensory fibers that previously innervated the amputated limb, and that these fibers remain functional for decades after limb loss,” said Doug Weber, the DARPA program manager. “HAPTIX will try to tap in to these biological communication pathways so that users can control and sense the prosthesis via the same neural signaling pathways used for intact hands and arms.”

In addition to the improved motor performance that restored touch and proprioception would convey to the user, mounting evidence suggests that sensory stimulation in amputees may provide important psychological benefits such as improving prosthesis “embodiment” and reducing the phantom limb pain that is suffered by approximately 80 percent of amputees. For this reason, DARPA seeks the inclusion of psychologists in the multi-disciplinary teams of scientists, engineers, and clinicians proposing to develop the electrodes, algorithms, and electronics technology components for the HAPTIX system. Teams will need to consider how the use of HAPTIX system may impact the user in several important domains including motor and sensory function, psychology, pain, and quality of life.

“We have the opportunity to not only significantly improve an amputee’s ability to control a prosthetic limb, but to make a profound, positive psychological impact,” Weber said. “Amputees view existing prostheses as if they were tools, like a wrench, used only to perform a specific job, so many people abandon their prostheses unless absolutely needed. We believe that HAPTIX will create a sensory experience so rich and vibrant that the user will want to wear his or her prosthesis full-time and accept it as a natural extension of the body. If we can achieve that, DARPA is even closer to fulfilling its commitment to help restore full and natural functionality to wounded service members.”

The program plan culminates with a 12-month, take-home trial of the complete HAPTIX prosthesis system. To aid performers in the completion of the steps necessary to achieve regulatory approvals for human trials, DARPA consulted with the U.S Food and Drug Administration to incorporate regulatory timelines into the program process.

“Once development of the HAPTIX system is complete, we want people to benefit immediately and be able to use their limb all day, every day, and in every aspect of their lives,” Weber said. “The experience needs to be comfortable and easy. Take-home trials are the first step in making that vision a reality.”

If it is successful, the HAPTIX program will create fully-implantable, modular, and reconfigurable neural-interface microsystems that communicate wirelessly with external modules, such as the prosthesis interface link. Because such technology would have broad application and could fuel future medical devices, HAPTIX also plans to fund teams to pursue the science and technology that would support next-generation HAPTIX capabilities.

Full details of the HAPTIX opportunity are available on the Federal Business Opportunities website at: http://go.usa.gov/kyjJ.

Phantom limb pain relieved when amputated arm is put back to work

Max Ortiz Catalan has developed a new method for the treatment of phantom limb pain (PLP) after an amputation. The method is based on a unique combination of several technologies, and has been initially tested on a patient who has suffered from severe phantom limb pain for 48 years. A case study shows a drastic reduction of pain.

People who lose an arm or a leg often experience phantom sensations, as if the missing limb were still there. Seventy per cent of amputees experience pain in the amputated limb despite that it no longer exists. Phantom limb pain can be a serious chronic and deteriorating condition that reduces the quality of the person´s life considerably. The exact cause of phantom limb pain and other phantom sensations is yet unknown.

Phantom limb pain is currently treated with several different methods. Examples include mirror therapy, different types of medication, acupuncture and hypnosis. In many cases, however, nothing helps. This was the case for the patient that Chalmers researcher Max Ortiz Catalan selected for a case study of the new treatment method he has envisaged as a potential solution.

The patient lost his arm 48 years ago, and had since that time suffered from phantom pain varying from moderate to unbearable. He was never entirely free of pain.

The patient´s pain was drastically reduced after a period of treatment with the new method. He now has periods where he is entirely free of pain, and he is no longer awakened by intense periods of pain at night like he was previously.
The new method uses muscle signals from the patient´s arm stump to drive a system known as augmented reality. The electrical signals in the muscles are sensed by electrodes on the skin. The signals are then translated into arm movements by complex algorithms. The patient can see himself on a screen with a superimposed virtual arm, which is controlled using his own neural command in real time.

”There are several features of this system which combined might be the cause of pain relief” says Max Ortiz Catalan. “The motor areas in the brain needed for movement of the amputated arm are reactivated, and the patient obtains visual feedback that tricks the brain into believing there is an arm executing such motor commands. He experiences himself as a whole, with the amputated arm back in place.”

Modern therapies that use conventional mirrors or virtual reality are based on visual feedback via the opposite arm or leg. For this reason, people who have lost both arms or both legs cannot be helped using these methods.

”Our method differs from previous treatment because the control signals are retrieved from the arm stump, and thus the affected arm is in charge” says Max Ortiz Catalan. ”The promotion of motor execution and the vivid sensation of completion provided by augmented reality may be the reason for the patient improvement, while mirror therapy and medicaments did not help previously.”

A clinical study will now be conducted of the new treatment, which has been developed in a collaboration between Chalmers University of Technology, Sahlgrenska University Hospital, the University of Gothenburg and Integrum. Three Swedish hospitals and other European clinics will cooperate during the study which will target patients with conditions resembling the one in the case study – that is, people who suffer from phantom pain and who have not responded to other currently available treatments.

The research group has also developed a system that can be used at home. Patients will be able to apply this therapy on their own, once it has been approved. An extension of the treatment is that it can be used by other patient groups that need to rehabilitate their mobility, such as stroke victims or some patients with spinal cord injuries.

Amputee pain linked to brain retaining picture of missing limb

Changes in the brain following amputation have been linked to pain arising from the missing limb, called ‘phantom pain’, in an Oxford University brain imaging study.

Arm amputees experiencing the most phantom limb pain were found to maintain stronger representation of the missing hand in the brain – to the point where it was indistinguishable from people with both hands.

The researchers hope their identification of brain responses correlated with the level of phantom pain can aid the development of treatment approaches, as well as increase understanding of how the brain reorganises and adapts to new situations.

The Oxford University researchers, along with Dr David Henderson-Slater of the Nuffield Orthopaedic Centre, report their findings in the journal Nature Communications.

‘Almost all people who have lost a limb have some sensation that it is still there, and it’s thought that around 80% of amputees experience some level of pain associated with the missing limb. For some the pain is so great it is hugely debilitating,’ says first author Dr Tamar Makin of the Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB) at Oxford University.

Treatments for phantom limb pain tend to be limited to standard drugs for pain relief. The origin of the pain is not well understood. There may be many factors that lead to the pain, including injured nerve endings where the limb was lost and changes in the brain areas connected with the missing limb.

Lynn Ledger, a 48 year old trained therapist and advisor to charities on management training from Nottingham, took part in the study. She had her left arm amputated halfway between the elbow and shoulder in May 2009 after radiotherapy for a rare form of cancer failed to deal with an extensive tumour in her arm. She experiences severe pain as if it was coming from the missing limb.

‘I’ve pretty much tried everything to deal with the pain but nothing has worked,’ Lynn says. ‘There are no drug treatments that work because the condition is not fully understood yet. I can only use various distraction techniques, breathing exercises and mental imagery techniques, to help me manage the pain.

‘It’s very hard to describe the pain to others. I have a nonexistent limb, but I still sense it and feel pain. It’s like: imagine you are wearing a lady’s evening glove that stretches from the fingers up the arm past the elbow. But everywhere the glove covers, it’s as if it’s constantly crushing your arm. There are also shooting pains and intensely painful burning sensations that come and go, but the crushing pain is constant.

‘When I heard about this study I wanted to be involved as it was trying to improve people’s understanding of the condition.’

Kirsty Mason from Bracknell is 22 and about to start a new job as a support worker for people with mental health problems, as well as being an assessor for disabled students for their assisted technology needs. She lost her right arm four years ago just below the elbow after blacking out at a train station and falling on to the rails just ahead of a train coming in. She woke to find a wheel stopped on her arm. Since then she’s learned to write with her left hand and began driving last year. She also took part in the brain imaging study.

‘With me it’s all or nothing,’ Kirsty says of her phantom pain. ‘I get the usual pins and needles and a constant niggling pain that I can shut out by doing other things. But the worst pain is a kind of burning. It’s less frequent but it’s intense: 90-100 on the scale. It sounds silly, but the only thing I can do is stick my hand in a freezer. It numbs it.

She says: ‘I can feel my fist clenching, my fingernails digging in. I can see the hand isn’t there but the sensation is so realistic. If someone throws me a ball, I’ll move both hands to catch it. I’ll put out both hands if I fall over.’

The Oxford University team used MRI imaging to study how the phantom limb pain felt by people who have had an arm amputated is related to changes in the brain.

They compared MRI data for 18 amputees, with differing levels of phantom pain, with 11 individuals born with one hand through a limb deficiency and a control group of 22 adults with two full limbs.

The amputations had been done 18 years ago on average, but the participants still experienced sensations for the missing arm. By asking them to move the fingers of the phantom limb while in the MRI scanner, the researchers were able to look at how the missing hand is represented in the brain.

They found that the brain maintained its representation of the hand, even though the limb was no longer there. The extent to which the representation was maintained was linked to the strength and frequency of the pain the amputees felt: those feeling the greatest pain retained the strongest representation of the missing hand.

‘We were astonished to find that in amputees experiencing strong phantom pain, the brain’s response was indistinguishable from that seen in people with intact limbs,’ says Dr Makin.

The researchers found that the amount of grey matter in the phantom hand area of the brain was reduced in amputees compared to those with two hands. But again this was linked to the amount of pain amputees felt. Those experiencing stronger pain showed less structural degeneration in the missing hand area following the loss of the limb.

However, while those with strong phantom limb pain maintained the local brain structure and function for the missing hand, there was evidence that connections to other parts of the brain were disrupted more.

In particular, the representation of the missing hand was more out of synch with the area looking after the other hand on the opposite side of the brain.

Dr Makin says: ‘Most people experience “phantom” sensations in a missing limb after amputation. This disconnect between the physical world and what they are experiencing appears to be linked to a functional detachment in the brain. There seem to be reduced connections between the missing limb part of the brain and the rest of the cortex that’s involved in movement.

‘Our results may encourage rehabilitation approaches that aim to re-couple the representation of the phantom hand with the external sensory environment.’