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Man controls new prosthetic leg using thought alone
THIS WEEK
Colin Barras
A MAN missing his lower leg has gained precise control over his prosthetic limb, just by thinking about moving it – all because his unused nerves were preserved during the amputation and diverted to his thigh where they communicate with a robotic leg. He can now seamlessly switch from walking on level ground to climbing stairs and can even kick a football around (see him in action at bit.ly/roboticleg). During traditional amputation, sensory nerves are severed and lose their function. In 2006, Todd Kuiken and his colleagues at the Rehabilitation Institute of Chicago realised they could preserve some of that functionality by rerouting sensory nerves and attaching them to another part of the body. The nerve signals were then available for a robotic limb, enabling a person to control their prosthesis with the same nerves they had originally used to control their real limb. Kuiken’s team first attempted the procedure – called targeted muscle reinnervation (TMR) – on
Lack of folic acid in pregnancy hits generations WHETHER or not a mother has enough folic acid during pregnancy could affect not only the health of the child, but also that of future generations. That’s the suggestion from a study in mice showing that folic acid deficiency triggers abnormalities in their pups and grandpups. It is well known that a lack of folic acid – a vitamin necessary for protein 14 | NewScientist | 5 October 2013
people who had to have their arm removed. Now he has performed TMR for the first time on a leg amputation. During the surgery, the team rerouted the two main branches of the patient’s sciatic nerve to muscles in the thigh. One branch controls the calf and some foot muscles, the other handles outside leg muscles and some more foot muscles. After a few months, the man could control his thigh muscles by thinking about using his missing leg. The next step was to link up a prosthesis. The robot leg in question is already very sophisticated: it carries a number of mechanical sensors including gyroscopes and accelerometers, and uses information from these sensors for certain walking styles. Kuiken’s team reckoned that the leg would be even more useful if it could infer the user’s intended walking style with information from the sciatic nerve. So first, they asked their volunteer to try to make movements with his missing leg – flexing the foot, for instance – while they monitored the pattern
formation – during pregnancy can result in birth defects or low birth weight, but how it does so is unclear. To investigate, Erica Watson at the University of Cambridge bred mice with a mutation in the MTRR gene, involved in folic acid metabolism. The mutation’s effect is similar to withdrawing dietary folic acid but is easier to control experimentally. When the mutated mice were mated with normal mice, some of the fetuses developed abnormalities such as heart defects and spina bifida. Only their siblings without defects survived to term and when
rehabilitation institute of chicago
Preserved nerves control robot leg
–I think therefore I walk–
of electric signals from the redirected nerves in the thigh muscles. Then they programmed the prosthesis to flex its foot whenever it detected that pattern. Using just mechanical sensor data, the robotic leg made the correct movement about 87 per cent of the time. With additional nerve data, the success rate rose to 98 per cent, and there were no critical errors, which increase the
risk of the user losing balance (NEJM, doi.org/n2h). “There’s a lot you can do with physical sensors but at some point you really need to know the user’s intent,” says Michael Goldfarb at Vanderbilt University in Nashville, Tennessee, who helped design the robot leg. “This new generation of prostheses can pretty much do whatever the healthy limb can do.” n
these were mated with normal mice, the next generation had the same problems, as did two subsequent generations (Cell, doi.org/n24). The effects occurred even though the pups and grandpups were free of the MTRR mutation, which suggests they were inherited not through DNA itself but through changes in the gene-switching system, says Watson. This “epigenetic” system turns
genes on and off through the addition of chemical tags, such as methyl groups. Until recently, it was assumed that these epigenetic marks were wiped clean after each generation. But when Watson’s team examined the DNA of offspring of mice deficient in folic acid and those of the next generation, they found widespread changes in methylation. The work supports the growing evidence that trans-generational epigenetic changes exist and are important for human health, says Tim Spector of King’s College London. Linda Geddes n
“The mouse pups had abnormalities because one of their grandparents had been folic acid deficient”
Colin Barras
A MAN missing his lower leg has gained precise control over his prosthetic limb, just by thinking about moving it – all because his unused nerves were preserved during the amputation and diverted to his thigh where they communicate with a robotic leg. He can now seamlessly switch from walking on level ground to climbing stairs and can even kick a football around (see him in action at bit.ly/roboticleg). During traditional amputation, sensory nerves are severed and lose their function. In 2006, Todd Kuiken and his colleagues at the Rehabilitation Institute of Chicago realised they could preserve some of that functionality by rerouting sensory nerves and attaching them to another part of the body. The nerve signals were then available for a robotic limb, enabling a person to control their prosthesis with the same nerves they had originally used to control their real limb. Kuiken’s team first attempted the procedure – called targeted muscle reinnervation (TMR) – on
Lack of folic acid in pregnancy hits generations WHETHER or not a mother has enough folic acid during pregnancy could affect not only the health of the child, but also that of future generations. That’s the suggestion from a study in mice showing that folic acid deficiency triggers abnormalities in their pups and grandpups. It is well known that a lack of folic acid – a vitamin necessary for protein 14 | NewScientist | 5 October 2013
people who had to have their arm removed. Now he has performed TMR for the first time on a leg amputation. During the surgery, the team rerouted the two main branches of the patient’s sciatic nerve to muscles in the thigh. One branch controls the calf and some foot muscles, the other handles outside leg muscles and some more foot muscles. After a few months, the man could control his thigh muscles by thinking about using his missing leg. The next step was to link up a prosthesis. The robot leg in question is already very sophisticated: it carries a number of mechanical sensors including gyroscopes and accelerometers, and uses information from these sensors for certain walking styles. Kuiken’s team reckoned that the leg would be even more useful if it could infer the user’s intended walking style with information from the sciatic nerve. So first, they asked their volunteer to try to make movements with his missing leg – flexing the foot, for instance – while they monitored the pattern
formation – during pregnancy can result in birth defects or low birth weight, but how it does so is unclear. To investigate, Erica Watson at the University of Cambridge bred mice with a mutation in the MTRR gene, involved in folic acid metabolism. The mutation’s effect is similar to withdrawing dietary folic acid but is easier to control experimentally. When the mutated mice were mated with normal mice, some of the fetuses developed abnormalities such as heart defects and spina bifida. Only their siblings without defects survived to term and when
rehabilitation institute of chicago
Preserved nerves control robot leg
–I think therefore I walk–
of electric signals from the redirected nerves in the thigh muscles. Then they programmed the prosthesis to flex its foot whenever it detected that pattern. Using just mechanical sensor data, the robotic leg made the correct movement about 87 per cent of the time. With additional nerve data, the success rate rose to 98 per cent, and there were no critical errors, which increase the
risk of the user losing balance (NEJM, doi.org/n2h). “There’s a lot you can do with physical sensors but at some point you really need to know the user’s intent,” says Michael Goldfarb at Vanderbilt University in Nashville, Tennessee, who helped design the robot leg. “This new generation of prostheses can pretty much do whatever the healthy limb can do.” n
these were mated with normal mice, the next generation had the same problems, as did two subsequent generations (Cell, doi.org/n24). The effects occurred even though the pups and grandpups were free of the MTRR mutation, which suggests they were inherited not through DNA itself but through changes in the gene-switching system, says Watson. This “epigenetic” system turns
genes on and off through the addition of chemical tags, such as methyl groups. Until recently, it was assumed that these epigenetic marks were wiped clean after each generation. But when Watson’s team examined the DNA of offspring of mice deficient in folic acid and those of the next generation, they found widespread changes in methylation. The work supports the growing evidence that trans-generational epigenetic changes exist and are important for human health, says Tim Spector of King’s College London. Linda Geddes n
“The mouse pups had abnormalities because one of their grandparents had been folic acid deficient”