August 7, 2020

A stimulus to walk again | Science



The three people with spinal cord injury who have recovered part of the movement of their legs and (in two cases) return to walk in controlled conditions constitute the scientific news of more impact that we have known this week. Read it in Matter. Experts agree that this is a very encouraging development, but also that, at the moment, it is only a proof of principle. The three participants in the study did not have a complete resection of the spinal cord, but only partial, and had a residual movement of the legs. This raises questions about how many people this technique can help. Some estimates speak of hundreds of thousands of people in the world. But only if they have residual motor function, which is not so common.

The technique differs from other strategies based on electrodes implanted in the brain and exoskeletons controlled by these signals. It consists of an epidural electrical stimulation (in the lumbosacral area, below the kidneys), but with temporarily organized stimulation not to interfere with the residual signals that travel from the legs to the brain. The stimulation is below the spinal cord injury, and what it does is amplify the residual signals that get there from the brain.

The scientists began by investigating the precise areas of the medulla that are involved in moving the hip, extending the ankle and other movements involved in walking. Then they programmed a sequence of electrical pulses in time and position to encode that movement. But electrical stimulation does not generate movement by itself. Needs the patient's voluntary orders. It's an amplification based on the call Hebb's law: neurons that shoot together, they end up connecting together.

In just two days the patients experienced a fairly natural sensation of movement; in a week, they could walk with the help of a crane that held some of its weight. After six months of exercises and electrical stimulation, they continued to improve until, finally, they could turn off the stimulator. Two patients are already on crutches, the third can only move their legs while lying down.

A test of principle that opens hopes, but that the authors of the work advise us to take with caution. These devices are not going to generalize immediately. Only safety studies will take more than three years, and the technique is complex, expensive and expensive. We need to advance much more, but now we know that the strategy works for some patients, and this is the best stimulus to move forward.

THE SCIENCE OF THE WEEK It is a space in which Javier Sampedro analyzes scientific news. Subscribe to the newsletter of Matter and you will receive it every Saturday in your email, along with a selection of our best news of the week.

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