Spinal cord injuries are life-altering, as they prevent the transmission of nerve impulses past the point of injury. That means no sensory inputs make it to the brain, and no signals from the brain make it to the muscles normally controlled by the brain. But improvements in our understanding of neurobiology have raised the hope that we can eventually restore some control over paralyzed limbs.

Some of these efforts focus purely on nerve cells, attempting to get them to grow through the damage at the site of injury and restore a functional spinal cord. Others attempt to use electronics to bypass the injury entirely. Today, there was very good news for the electronics-focused effort: researchers have designed a spinal implant that can control the leg muscles of paralyzed individuals, allowing those individuals to walk with assistance within hours of the implant being activated. //

An alternative to that type of biological repair is what you might consider an electronic bypass. In its most sophisticated form, a bypass would involve an implant that registers neural activity, located either in the brain or in the spinal cord closer to the brain than the injury. This is then paired with some sort of hardware—potentially another implant—on the far side of the injury that stimulates the nerves based on the information read by the other implant.

A less sophisticated version of this is to simply have preprogrammed behaviors you want to control, such as the leg movements involved in walking. That is the approach used in the recent work. But, as will become very clear, "less sophisticated" leaves a wide-open space for some very sophisticated work. //

The results were astonishing. Prior to activating the implant, none of the three participants could initiate any sort of muscle activity when attempting to take a step. The same day that the model was trained, all of the subjects could take steps on a treadmill if they were supported. The model was able to generate the right series of currents to stimulate the leg muscles appropriately.

Out for a walk and more
With three days of fine-tuning, the participants were able to walk around a room if given sufficient support. Eventually, they were able to stand unaided and walk supported only by a walker—their legs were controlled via an implant in their abdomen, which responded to triggers on the handles of the walker. One volunteer was even able to go up stairs.

Separate programs were also developed that allowed the subjects to ride recumbent bicycles or to paddle a kayak.

One striking thing is that two of the subjects actually regained the ability to exert a bit of voluntary muscle control in their formerly paralyzed limbs. Apparently, a bit of weak connectivity was still present but unable to provide a signal strong enough to trigger muscle activity. With extended activity, those weak connections were gradually strengthened, providing a complete pathway from brain to muscle.