People with amyotrophic lateral sclerosis (ALS) gradually lose the ability to move their muscles. In the advanced stage, they are fully conscious in a state in which they can no longer communicate with the outside world – the locked-in syndrome. Researchers have now developed a system that enables communication without any muscle movement. Electrodes implanted in the brain measure the brain signals and decode them as “yes” or “no”. In this way, the patient can, for example, select letters that are read aloud and form words and sentences from them.
Amyotrophic lateral sclerosis is an incurable disease in which the neurons of the motor nervous system degenerate, leading to progressive paralysis. The best-known patient was the astrophysicist Stephen Hawking. While Hawking was still able to move his facial muscles and thus control a speech computer, other patients with more rapidly progressing forms of the disease are often in a state in which they can no longer even control the eye muscles at will. Since previous communication systems – including those based on a brain-computer interface (BCI) – require at least minimal muscle movements, these patients had no way of communicating with the outside world.
Patient with complete locked-in syndrome
A team led by Ujwal Chaudhary from ALS Voice gGmbH in Mössingen in the district of Tübingen has now developed a system that does not require any muscle movement. The reason for this was a request from the family of a patient with a rapidly progressing form of ALS. When he was diagnosed with the disease in 2015, the patient was 30 years old. In the same year he lost his ability to walk and speak, since 2016 he has been artificially fed and ventilated. He initially communicated with his family through eye movements, but when it became apparent that he was about to lose that ability too, his family turned to Chaudhary and his colleagues.
In a clinical case study, the researchers provided patients with a system they developed that measures their brain signals and derives the answers “yes” and “no” from them. “This study answers a long-standing question, namely whether people with complete locked-in syndrome, who have lost all voluntary muscle control, including eye and mouth movements, also lose their brain’s ability to process commands for communication generate,” says co-author Jonas Zimmermann from the Wyss Center in Geneva. “Successful communication using BCIs has already been demonstrated in people with paralysis. However, to our knowledge, this is the first study that has succeeded in communicating with a person who is incapacitated and for whom the BCI is now the only means of communication.”
electrodes in the brain
The brain-computer interfaces commonly used to date are often non-invasive. To use them, electrodes are attached to the scalp that record brain signals. In the case of the completely paralyzed patient, however, these signals were too imprecise to be reliably decoded. Chaudhary and his team therefore implanted two tiny plates with microelectrodes in his motor cortex. If the patient imagines movements, the brain activity in this area changes. In numerous training sessions, the patient has learned to consciously modulate his brain activity in such a way that the electrodes can record and recognize this. He was helped by a feedback system that converts the changes in the firing rate of the corresponding neurons into acoustic signals.
Patients can now control their brain signals in such a way that the computer can derive the answers “yes” and “no” from them. In this way he can answer questions, but also spell words and sentences. A spelling program reads him the letters of the alphabet and he confirms the correct letter with “yes”. However, it takes a while for a whole sentence to come together in this way – on average, the patient can “write” about one letter per minute with this system.
communication with family
The system enables patients to still communicate with their fellow human beings at all. Many of his messages relate to his care, the researchers report. For example, he shared that he would like to get gel for his dry eyes more often, what clothes he would like to wear at night, but also what music he would like to listen to at the moment. He also made suggestions for improving the system himself. Among other things, the researchers introduced a word recognition program at his suggestion. He also uses the system to communicate with his wife and son.
“This study has also shown that the system can, in principle, be used at home with the involvement of the family or the nursing staff. This is an important step for people with ALS who are cared for outside the hospital,” says Zimmermann’s colleague George Kouvas. “This technology, which will benefit a patient and their family in their own environment, is a great example of how technological advances in the BCI field can be implemented to have a direct impact.” are developing that can measure signals from other areas of the brain and could eventually make it possible to directly decode imagined speech and convert it into audible speech.
Source: Ujwal Chaudhary (ALS Voice gGmbH, Mösslingen, Germany) et al., Nature Communications, doi: 10.1038/s41467-022-28859-8