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Latest Term: Lower Extremity Functional Electrical Stimulation

Lower extremity functional electrical stimulation is a type of neuromuscular electrical stimulation in which long-term embedded prosthetics electrically generate the same neural signals the brain would normally use to control the muscles in a person's legs, and transmit them into the trunk nerves heading into those muscles.

This type of Functional Electrical Stimulation (FES) is used when the spinal cord or a major trunk nerve in the leg has been severed. The resulting paralysis renders the limb non-functional even though there is nothing wrong with the muscles. As the brain's own signals cannot get through, they must be artificially generated instead.

In cases of severe damage, the severed nerves are highly unlikely to reconnect, and so an implant is placed into the affected nerve bundles just after the break. Its job is to use electrode arrays to transmit the neural codes – the brain's equivalent of function calls to control the muscles of the body – into these bundles, and restore function.

The opposite number of FES or a procedure known as TMR or Targeted Muscle Re-enervation. This process uses a similar electrode array setup to read the neural codes as they transmit down the nerve bundle, by picking up minute changes in the electrical activity of the muscles they are embedded in.

In an ideal situation, a lower extremity functional electrical stimulation prosthetic would have both parts: TMR before the damaged area, to detect what signals the brain is trying to send, and FES after the damaged area to relay those signals back into the target muscles. In theory this setup could render nerve damage invisible, bypassing the damaged area completely.

In practice, both TMR and FES are presently inexact sciences, with the current impossibility of directly tapping into every individual neuron in the bundle directly, and the multitude of neural codes whose full effects remain unknown to us.

Work is continually proceeding to address both issues, however for the moment, a lower extremity FES prosthetic is typically controlled by a control console operated by the patient's hands. Different controls thus ordering their own legs to begin specific preset series of muscle movements. This allows the individual to perform tasks such as walking, climbing stairs, descending stairs, standing up and sitting down. This type of interface does not allow much in the way of individual customisation or spontaneous action, still it prevents the muscles in the legs from atrophying due to disuse and gives the individual back some degree of independence.

See Also: NMES, Neural Coding, TMR, BMI

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