Alejandro Ortiz became deaf due to meningitis when he was two and a half years old. The infection spread to his inner ears, where it destroyed specialised cells in charge of transforming the mechanical impulse of sound into the electrical impulse of the auditory nerve. At age four, Ortiz could hear again, but the sensation was unfamiliar. Sound didn’t arrive at his brain through the ear; rather, it entered via a small microphone attached to the side of his head, which relayed radio signals to minute electrodes implanted in his auditory nerve. Ortiz is now 27, he can hear and speak fluently and he lives in Spain. “The cochlear implant had a great impact on my life,” he claims.
Just a few decades ago, direct and controlled stimulation of the nervous system belonged in the realm of science-fiction. In fact, many of the brain’s inner workings are still a mystery to scientists and, therefore, they pose a challenge for physicians when something goes wrong. But the arrival of neurotechnology, based on the physical connection of machines to the nervous system, has enabled medical feats beyond those achieved by pharmacology. The new techniques are used to control symptoms of epilepsy and Parkinson’s disease, to speed up rehabilitation in stroke patients and they have even enabled tetraplegic people to walk.
Cochlear implants were one of the first medical applications of neurotechnology, approved for therapeutic use in adults during the 1980s and for children at the turn of the century. Today, hundreds of thousands of people with a hearing disability benefit from them (324,000 estimated users in 2012). It’s not a perfect treatment, because the implanted electrodes lack the fine-tuned resolution of cochlear cells, required to distinguish every sound frequency in the audible spectrum. Noisy environments, rooms with reflective surfaces and crowded conversations make hearing difficult for users, too.
In addition, everyone who bears the implant must learn to listen from scratch. Ortiz attended hearing school and several specialists during his childhood and adolescence to train his brain in the interpretation of the electrical signals generated by his cochlear implant. He urges anyone who can benefit from the device to take the step as early as possible. “Language is developed faster in childhood,” he says.
Recreate the sense of touch
Fast-forward to the year 2019. For the first time, the same technique used to recreate the sense of hearing has enabled surgeons to recreate the sense of touch in people with a different sort of disability: leg amputees. An international team of scientists led by the EPFL research centre in Switzerland has managed to fuse with their bionic prosthetics three people who had their legs removed above the knee. All three have regained the ability to walk through obstacles intuitively.
“After all these years, I could feel my leg and my foot again, as if it were my own leg,” Djurica Resanovic, one of the amputees, reported to the media after his procedure. “It was very interesting. You don’t need to concentrate to walk, you can just look forward and step. You don’t need to look at where your leg is to avoid falling.” This technology sends information directly to the nervous system, like a cochlear implant. The opposite process, ‘reading’ brainwaves to operate an external machine, is employed by other brain-machine interfaces like the mind-controlled wheelchair.
Resanovic’s bionic leg is equipped with pressure and movement sensors, which send wireless signals to electrodes permanently inserted in the tibial nerve of his stump—just like Ortiz’s microphone sends wireless signals to the electrodes in his inner-ear. Resanovic can physically feel the prosthetic leg as an extension of his body, even when he’s wearing earplugs and a blindfold. “I could tell when they touched the [big toe], the heel, or anywhere else on the foot. I could even tell how much the knee was flexed,” he reported. Clinical trials have demonstrated that this sort of bionic technology reduces fatigue and the appearance of phantom pain frequently linked to limb amputations.
Since the 1980s, direct electrical stimulation of the nervous system is also the technique used to halt incapacitating epileptic seizures and the symptoms of other movement disorders like Parkinson’s disease. For this, electrodes are implanted directly in the skull, a method known as deep brain stimulation, or DBS. The same one has been adapted to achieve direct electrical stimulation of the spinal cord, a procedure which recently allowed people completely paralysed through tetraplegia to walk again. In the future, however, medical neurotechnology will not only send electrical impulses to the brain and spine, it will receive signals in turn, recreating the bidirectional communication that truly takes place between the nervous system and every organ in the body.
Already there are prototypes for mind-controlled robotic arms and robotic hands, but none of these integrate the process of reading brainwaves with sensory feedback of the sort provided by Resanovic’s bionic leg. Monitoring thought patterns, or brainwaves, through electroencephalography (EEG) is used for cognitive enhancement, which has therapeutic applications for rehabilitation of stroke patients and, experimentally, in the prevention of dementia and Alzheimer’s disease. In its simplest form, the treatment takes the form of an easy mental agility video game which only allows the users to progress when the EEG monitor recognises that the brain is receptive to the learning process. This way, the gaming effort is focused on rerouting or strengthening relevant neural pathways.
Meddling with the brain raises a troubling prospect: does medical neurotechnology change patients’ sense of self? It’s a reasonable question which biotethicists have pondered since the turn of the century—after all, the brain is the seat of consciousness, constructed from our private thoughts and from feelings of the outside world which we all collect via the nervous system. As it turns out, some people who have received DBS treatment do report feeling changes to their identity. The ramifications of this issue will be explored in the next article of the series.