Implanted electrodes could provide movement to paralysed limbs

An array of implanted electrodes have been used to control the movement of arms and legs, a development that could one day be applied to people with spinal cord paralysis.

The work carried out in the US is said to have focused on controlling electrical stimulation pulses delivered to peripheral nerve fibres. When a patient is paralysed, one of the possible causes is damage to the spinal cord, which along with the brain makes up the central nervous system. The brain still works, as do motor and sensory nerves in the peripheral nervous system, but electrical signals can’t flow between those nerves and the brain because of the spinal cord injury.

That communication problem is what researchers sought to address, through experiments that involved transmitting precisely controlled electrical pulses into nerves activating plantar-flexor muscles in an ankle of an anesthetised cat.

V John Mathews, professor of electrical engineering and computer science in the Oregon State University College of Engineering, lead researcher Mitch Frankel, then a Ph.D. student at the University of Utah, and three other researchers, all faculty members at Utah, conducted the study.

The researchers sent pulses using an optimised PIV controller — proportional-integral-velocity — and the cat’s nerves received them via a 100-electrode array whose base measured 16 square millimetres.

Thanks to specific electrodes being able to activate the right nerve fibres at the right times, the controller made the cat’s ankle muscles work in what has been described as a smooth, fatigue-resistant way.

The results suggest that a paralysed person might one day be equipped with a wearable, smartphone-sized control box that would deliver impulses to implanted electrodes in his or her peripheral nervous system, which would enable a degree of movement.

“Say someone is paralysed and lies in bed all day and gets bed sores,” Mathews said in a statement. “Early versions of this technology could be used to help the person get up, use a walker and make a few steps. Even those kinds of things would have an enormous impact on someone’s life, and of course we’d like people to do more. My hope is in five or 10 years there will be at least elemental versions of this for paralysed persons.”

The research is described in a paper – Control of Dynamic Limb Motion Using Fatigue-Resistant Asynchronous Intrafascicular Multi-Electrode Stimulation -published in Frontiers in Neuroscience.