Six men and two women who had completely lost the use of their lower limbs all made significant progress, the researchers reported in the peer-reviewed journal Scientific Reports.
In four cases, doctors were able to upgrade their status to “partial paralysis,” an unheard-of level of improvement using non-invasive techniques.
One of them — a 32-year-old woman paralysed for more than a decade — may have experienced the most dramatic transformation.
At the outset of the trial, undertaken at a clinic in Sao Paulo, Brazil, she was unable to stand, even with the help of braces.
Within 13 months, she could walk with the help of braces and a therapist, and could produce a walking motion while suspended from a harness.
“We couldn’t have predicted this surprising clinical outcome when we began the project,” said Miguel Nicolelis, a neuroscientist at Duke University in North Carolina and the main architect of the rehabilitative research.
“Until now, nobody has seen recovery of these functions in a patient so many years after being diagnosed with complete paralysis,” he told journalists in a phone briefing.
One of the women sufficiently recovered sensation — on her skin and inside her body — “that she decided to deliver a baby,” Nicolelis said. “She could feel the contractions.”
The innovative therapy combined several techniques to stimulate parts of the brain that once controlled the patients’ long-inactive limbs.
The underlying — but still unproven — theory is that this process provokes changes not only in the brain, but in the damaged spinal cord as well.
Nicolelis took the global spotlight in June 2014 when a paraplegic wearing a robotic bodysuit he co-designed delivered the symbolic first kick at football’s World Cup in Brazil.
In the new trials, rehabilitation began by learing how to operate a digital Doppelganger, or avatar, within a virtual reality environment.
At the same time, patients wore snug caps lined with 11 electrodes to record their brain activity through EEG, or electro-encephalography.
Initially, when they were asked to imagine walking while immersed in a digital 3D world, the parts of the brain associated with motor control of the legs failed to light up.
“If you said, ‘Use your hands,’ there was brain activity,” Nicolelis said. “But the brain has almost completely erased the representation of their lower limbs.”
After months of training, these long-dormant parts of the brain started to wake up.
At that point, the patients graduated to more challenging equipment that required some control over their posture, balance and ability to use upper limbs, including overhead harnesses — common in physical therapy centres — that carry the body’s weight.
They also used exoskeleton robotics not unlike the articulated, high-tech armour of comic book hero Iron Man.
Through all of this, the patients wore an arm sleeve equipped with a touch-technology, called haptic feedback, that uses a range of unique vibrations — something like the buzzing jolts gamers feel in hand-held controllers — to help train the brain.
When an avatar walks on sand, for example, the patient feels a different pressure than for grass or asphalt.
The patient’s brain creates the illusory feeling that he or she is walking without the assistance of devices.
What exactly happens in the body to allow for these improvements is still not clear.
At least one previous study, Nicolelis said, has shown that a large percentage of patients who are diagnosed as having complete paraplegia may still have some spinal nerves left intact.
“These nerves may go quiet for many years because there is no signal from the (cerebral) cortex to the muscles,” he speculated.
“Over time, training with the brain-machine interface could have rekindled these nerves.”
Even a small number of remaining nerve fibres “may be enough to convey signals from the motor cortical area of the brain to the spinal cord,” he suggested.
High-tech imaging confirms activity in the brain during training.
However, the scanning cannot be used to scrutinise the spinal cord due to the presence of reconstructive metal in the damaged area.
In 2014, three young paraplegics were able to voluntarily flex their knees, ankles and toes after US scientists placed implants in their lower spine, hailed as a breakthrough at the time.
And earlier this year, a US man paralysed in the arms was able to use his right hand to swipe a credit card and stir coffee thanks to a surgically-inserted chip that allowed his brain to communicate with computer linked to an electrode sleeve.
But the new results may be the first achieved without the use of any invasive devices.
With the eight patients now into their second year of training, Nicolelis is preparing a follow-up study looking at changes in their quality of life.
Most them recovered some degree of control of basic bodily functions, including bladder control and bowel function.
“There has also been improvement in sexual performance for the men,” said Nicolelis.
Some had recovered “the possibility of having sexual intercourse, and erections,” he said.