by Lauren Lin
“Locked-in syndrome” is used to describe a medical condition in which there is complete paralysis of all voluntary muscles in the body including most facial muscles. Individuals who have locked-in syndrome are conscious, have cognitive function, and are aware of their environment, but they cannot produce movements or speak. This condition is often caused by damage to the pons, a part of the brainstem that relays information to different parts of the brain. The damage can result from strokes, infections of the brain, or bleeding. Certain disorders like Amyotrophic Lateral Sclerosis (ALS), a motor neuron disease, can also cause total motor paralysis. Many people with locked-in syndrome can communicate through moving their eyes and/or blinking, but individuals with locked-in syndrome may eventually lose their ability to move their eyes, and so communication becomes extremely difficult.
Chaudhary, Xia, Silvoni, Cohen, and Birbaumer (2017) report on the potential for brain-computer interface (BCI) to offer a way for patients with ALS who are paralyzed to communicate. BCI research may involve invasive procedures like implanting electrodes in the brain or noninvasive technologies like functional magnetic resonance imaging (fMRI) and functional near-infrared spectroscopy (fNIRS) to record brain activity. The recorded brain activity then can be interpreted for what the user is communicating. Chaudhary et al. (2017) used fNIRS to measure the changes in blood flow by assessing oxygenated hemoglobin (O2Hb) and used electroencephalography (EEG) to measure brain waves of four patients who had no motor movement. The relative changes in oxygenated hemoglobin when patients responded to “true/yes” and “false/no” statements were significantly different from each other, and so fNIRS measurements were used to recognize whether the patient answered "yes" or "no". However, EEG measurements were not able to reliably discriminate between yes or no answers.
To train the patients to be able to answer questions using BCI, the researchers asked the patients to respond “yes” or “no” to personal statements with known answers like “Your husband’s name is Joachim” or “You were born in Berlin.” For each known statement with a clear “yes” answer, a similar statement with a clear “no” answer was also given. For example, if the statement “You were born in Berlin” was true, it could be paired with “You were born in Paris,” a false statement. The reverse was done for statements with clear “no” answers. The patients were explicitly told to think of “yes” or “no” answers but not to imagine the answer visually or auditorily so that the BCI would only be picking up on signals that correspond with “yes” or “no” sentiments rather than the look or sound of the words. The patients also received feedback on what their answer was interpreted as (e.g. “Your answer was recognized as ‘yes’”) during training.
The patients were asked a total of at least 200 sentences with known answers and 40 open questions or statements that asked about the person’s quality of life or questions of caretakers that only the patient could answer (e.g. “You have back pain.”). The four patients communicated using BCI with a correct response rate of 70% over the course of several weeks, which is above the level of chance (50%). Three of the four patients were asked open questions about their quality of life, such as “Are you happy?” and “I love to live.” These questions were asked repeatedly to ensure validity of the response. All three patients answered “yes,” which indicated an overall positive attitude towards their current situation and towards life.
BCI seems like a promising way for patients with paralysis in almost all voluntary muscles to communicate since it does not require any motor movements. However, the interpretations of the responses are not always correct, and so it is extremely important to take precautions like asking a single question multiple times. Additionally, BCI may not be accessible in all healthcare settings since it requires both the equipment needed to measure and interpret brain signals and the training for the patient to use it. Despite these limitations, BCI still has a lot of potential to provide a way for locked-in patients to convey their thoughts who may not have been able to previously, especially when considering that one of the patients included in the study had not been able to communicate for four years. The researchers of this study are hopeful that this technology could be a stepping stone towards improving the quality of life of patients who are in a locked-in state and even write that family members all “experienced substantial relief” when they were able to communicate with the patients and that they still use the system.