Amputees’ Brains Remember Their Lost Limbs For Decades

The 2016 Summer Paralympics will kick-off in Brazil in just one week. The Summer Paralympic Games, now in their 15th year, are vital in developing global awareness around disabled athletes and disability in general. Many of the athletes who will compete in these games are fitted with prosthetics – artificial devices that replace missing body parts.

These artificial devices can replace hands, arms, fingers, legs, feet, and even sockets like wrists and knee joints. In the 21st century, prosthetics aren’t anything new, but the field is advancing rapidly thanks to incredible scientific research and discovery. This development doesn’t mean they prosthetics are problem-free, however; they still cause issues to their users.

Now, a new study offers the possibility of a much improved generation of prosthetics – with the brain directly controlling the artificial limb.

What are prosthetics & who uses them?

Prosthetics are used by people who have lost a limb, whether through trauma, disease, or congenital issues. By far the leading causes of limb loss worldwide are diabetes and peripheral vascular disease. Other common contributors are accidents and war injuries.

The Brains Of Amputees Remember Lost Limbs Even Decades Later

In the United States alone, nearly 2 million people are currently living with limb loss. Worldwide statistics on limb loss are hard to come by, especially in developing countries where the percentage is higher.

Not all amputees use prosthetics, but studies estimate that just in the U.S., up to 185,000 amputations are performed each year. If even a fraction of that group is using prosthetics, it’s a vital field for study and development.

Prosthetics have many significant benefits, allowing people with limb loss to regain much of their quality of life – like many disabled athletes. But even the best or most high-tech prosthetics are wrought with negatives:

  • Cost is high, especially initially.
  • Some types require significant upkeep.
  • Many patients have much difficulty learning to use the artificial limbs and joints, as they require an entirely different set of brain input and output. This can lead to amputees avoiding their prosthesis despite their desires.

A new study by Oxford University, however, may help to develop neuroprosthetics: prosthetic limbs that the brain controls directly.

Study on Brain Function in Amputees

In people without limb loss, brains have detailed pictures of all intact body parts: hands and fingers, toes, feet and knees, etc. Until recently, it was understood that this picture could only be maintained via regular sensory input, or the direct movement from the limbs. Science has even taught that this so-called picture will eventually be erased or ‘written over’ if its primary sensory input ceases.

The conflict with this train of thought, however, has been that amputees have, for years, reported phantom sensations from amputated body parts – sometimes they can even ‘feel’ the movement when asked to move the amputated body part.

Is there anything to these phantom feelings? Could the brain still function without a limb – and if so, could the brain start pairing with the prosthetics, encouraging a quicker learning period for patients as they don’t have to start from scratch?

Oxford University’s Hand and Brain Lab set out to study brain activity in these phantom movements. The research team focused on finger and hand movement. They wanted to see whether there are similarities in brain activity regarding these movements in both amputees and people with actual, moving fingers and hands.

How the study worked

The brain’s ‘picture’ of the hand exists in the primary somatosensory cortex. Because long standing theory held that this picture can only be maintained via regular sensory input, without regular input, this picture would be ‘overwritten’ or otherwise erased. If that were indeed the case, those with amputated hands would have very low or no activity in the somatosensory cortex.

Scientists and researchers at the Hand and Brain Lab worked with a small group of participants:

  • Two amputees who’d lost their left hands (25 and 31 years ago respectively), but still reported phantom feelings of movement.
  • 11 people who have both hands, and are right-handed.

The individuals moved the fingers on their left hands while the research team observed brain activity, primarily that in the somatosensory complex.

The brain does remember

Elderly man and small boy sharing a park bench.

Researchers from Oxford concluded that the brain does not lose this picture, as previously thought, but instead maintains it, even decades after amputation.

Ms. Sanne Kikkert, leader of this study, summarized their conclusions: ‘While there was less brain activity related to the left hand in the amputees, the specific patterns making up the composition of the hand picture still matched well to the two-handed people in the control group.’

Essentially we can understand that the brain does reorganize and/or adapt when sensory inputs from limbs are lost, but that doesn’t erase the original function or ‘picture’ of a particular brain area.

These findings correlate with a different study of the brain’s visual cortex, another area that maintains ‘pictures’ from sensory input. In patients who have had limiting visual impact due to degenerative eyes diseases (i.e., macular degeneration), the brain still maintains the image of the unaffected visual field.

What do the findings mean?

Scientists and researchers have been exploring neuroprosthetics – the idea that prosthetic limbs could be directly controlled by the brain. Based on the previous thinking, an amputee’s brain wouldn’t be able to control the prosthetic because the amputation had halted the primary sensory input.

But if the brain does indeed maintain a representation of the fingers or limbs, as this study has found, neuroprosthetics may develop much sooner.

Artificial limbs that are controlled by the brain could lead to easier training and adoption of them, which in turn would vastly improve amputees’ quality of life. As more amputees opt into using prosthetics, the cost would decrease, allowing more people around the world to take advantage of this incredible alternative.

Do these findings mean the brain can change to adapt to any new circumstance? Are latent functions in the brain still able to be preserved? We know the brain is a mysterious, powerful organ (it is in animals, too), but these answers will require much more research before science can answer them for sure.

References: Oxford University, Bioengineering Institute Center for Neuroprosthetics – Worcester Polytechnic Institution, Wikipedia

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