Locked-in syndrome (LIS) is a rare but devastating neurological condition where someone loses their ability to move or speak. Individuals with LIS are fully conscious and mentally alert, but they can only make eye movements and are completely paralysed otherwise. LIS can be caused by a traumatic brain injury, demyelinating diseases, or a stroke. Individuals affected by LIS syndrome typically communicate through eye movements, such as blinking, and there is currently no cure for locked-in syndrome. However, recent advances in neurotechnology offer a hopeful avenue for allowing those affected by LIS to regain some sense of communication through brain-computer interface (BCI) technology. BCI technology is still in its early stages of research and development, but it offers a promising means of improving the quality of life for those affected by locked-in syndrome. 

Continue reading to learn more about brain-computer interfaces, their current applications and how they can be used to manage locked-in syndrome and allow those affected to communicate. 

Understanding locked-in syndrome

LIS occurs when there is paralysis of all voluntary muscles, except for muscles that control eye movement. It is caused by damage to the area of the brainstem known as the pons, and this damage will impact motor function. However, cognitive abilities such as consciousness and sleeping, as well as sensory functions such as seeing and hearing, will still be intact. 

There are three main types of locked-in syndrome, which include:¹

• Classical LIS: This is the most common type of LIS, which is when there is total paralysis, except for vertical eye movements
• Incomplete LIS: Incomplete LIS is similar to classical LIS; however, those with incomplete LIS will have some additional motor functions
• Total LIS: Total LIS occurs when someone has complete paralysis, including voluntary eye movements (e.g blinking or up-and-down eye movement)

Diagnosis & management

LIS is diagnosed through various clinical means, including brain imaging (e.g MRI and CT scan). These scans allow physicians to assess whether there is damage in the brain, particularly in the pons of the brainstem. Other clinical tests, such as an electroencephalogram (EEG), will assess brain activity in order to determine whether the patient has abnormal brain activity.² An important aspect of diagnosing locked-in syndrome is ruling out other conditions which may cause similar symptoms, and tests such as an electromyography, cerebral angiography, and cerebrospinal fluid (CSF) test, can allow physicians to rule out any other conditions and determine a definitive diagnosis. 

As of now, there is no effective treatment for locked-in syndrome. Individuals affected by LIS usually require extensive therapy and support to manage their condition. Because those with LIS may find it difficult to breathe on their own, they will usually require artificial support that will help them breathe (i.e a tracheotomy). In addition, they may also require a gastrostomy tube to help them receive food and drinks. In cases of incomplete LIS, where there is some motor function, patients may receive physical therapy to rehabilitate some movements.² In regard to their ability to communicate, some individuals with LIS can use assistive technology to communicate, such as alphabet boards or infrared eye movement sensors, which track eye movements to relay a message.¹

What are brain-computer interfaces (BCIs)?

Brain-computer interfaces are devices that allow for direct communication between the brain and an external device, offering a promising avenue for individuals with LIS to communicate. This technology works by assessing electrical signals in the brain and translating them into digital commands, which can allow individuals to control a computer, speech device or a neuroprosthetic.³ 

Essentially, BCIs work through these stages:

• Brain signals are measured through electrical activity tests (e.g EEG) or implanted electrodes. This process can be referred to as signal acquisition⁴ 
• The recorded brain signals are then processed and deciphered in order to determine the user’s intent⁴ 
• The processed data can then be translated into a command for a computer or external device
• This command will produce a device output, such as moving a computer cursor or stimulating a text-to-speech function

BCIs can be invasive or non-invasive, depending on whether they are inserted in the brain through a surgical method or utilised without surgery. Invasive BCIs have shown more accuracy in results; however, their use carries more risks and safety concerns, whilst non-invasive BCIs tend to be less accurate but carry fewer risks.  

Role of BCIs in the management of locked-in syndrome

Due to the limited forms of communication for individuals with LIS, many are compelled to communicate through eye movements, such as blinking or up-and-down eye movements, which tends to limit their communication to yes or no responses. BCIs could be a great tool that allows individuals affected by locked-in syndrome to communicate more effectively by reading their brain signals, processing the signals and then decoding them to initiate a command on an external output, such as a computer or speech device. This will enable better communication for individuals with LIS and allow them to expand their communication past yes/no responses. Outside of communication, BCIs may allow those with LIS to control other assistive devices, such as wheelchairs, with their brain signals. This impact could provide patients affected by locked-in syndrome with more autonomy and a better quality of life. 

Several studies have demonstrated the positive use of BCIs for the management of LIS. One clinical study done by researchers at the Wyss Centre for Bio and Neuroengineering, in collaboration with the University of Tubingen, showed positive results for their BCI in a patient with total LIS, where there is complete paralysis, even of the voluntary muscles that control eye movement. This was a two-year study that involved an invasive BCI where microelectrodes were implanted in the patient’s brain. The BCI, in this case, measures for yes or no responses. To form complete sentences or words, the alphabet is read aloud, and the BCI technology will measure and process the ‘yes’ or ‘no’ responses in the user’s brain signals. A patient who was unable to communicate, even through eye movements, was now able to form words and sentences through the use of the BCI technology.⁵ Other studies, such as the ones at UC San Francisco and BrainGate, have also shown similar positive results in their early stages of development. Despite this, BCI technology is still undergoing clinical trials and requires further research & development until it can be approved and established as a viable avenue for the management of LIS. 

Current challenges & future directions 

Although BCIs are a promising technology for managing LIS and allowing individuals affected by LIS to communicate, the technology still faces many challenges. Training users on BCIs requires a long period of time and continuous support, and the technology will also need to be continuously monitored for technical issues.⁶ Additionally, current BCI technologies take a long period of time to initiate a command. Companies like Neuralink are developing wireless BCI technology, using Bluetooth, to initiate a quicker response and improve user-friendliness. However, these devices still need to be tested and approved. Another challenge for BCI technologies is their invasiveness. Whilst non-invasive BCIs exist and provide some positive results, their accuracy and effectiveness are lower compared to invasive BCIs that are implanted directly. These invasive BCIs, however, carry more risks because they involve a surgical procedure.⁷ 

With the rapid progression of artificial intelligence, machine learning and other technological advancements, future systems for BCIs may be less invasive, work at a faster pace, require less technical monitoring, and be more user-friendly overall. Further research and clinical trials are needed in order to monitor the long-term effects of BCIs and their safety & efficacy. 

Summary

Locked-in syndrome imposes significant challenges on individuals with the condition through limiting their ability to move or communicate, despite having cognitive function and awareness. LIS has no cure or effective treatment, but brain-computer interfaces offer hope for individuals with LIS. This advanced form of neurotechnology allows individuals affected by LIS to communicate by measuring and processing their brain signals. BCI technology, however, is still in its early stages and requires further development and BCI in order to determine its effectiveness in the management of LIS. 

Ultimately, brain-computer interfaces represent a significant development in addressing the challenges caused by severe neurological impairments, such as those posed by locked-in syndrome.