Locked-in patients suffer from a rare neurological disorder. Their voluntary muscles, except those that control the eyes, are completely paralyzed. They can feel your touch, but can’t touch you back. They can hear you, but can’t speak. People in a less severe locked-in state can blink or vertically move their eyes to communicate. But the completely locked-in patients can’t even blink.
Measuring blood flow and oxygenation
Scientists have finally been able to decode the thoughts of and communicate with completely locked-in patients. Findings of the brain study were published in the journal PLOS Biology. The condition could be caused by brain injury, medication overdose, stroke, nervous system or circulatory system diseases such as Amyotrophic Lateral Sclerosis (ALS), which is also known as Lou Gehrig’s disease.
Niels Birbaumer of the Wyss Center for Bio and Neuroengineering in Switzerland and his colleagues used a brain-computer interface system to communicate with the patients. The system included an electroencephalography (EEG) cap that measures electric activity in the brain, and a functional near-infrared spectroscopy, which measures blood flow and oxygenation in the brain.
How locked-in patients responded to questions
The study involved four patients. Over a period of several weeks, they were asked “true or false” and “yes or no” type of questions. The patients were connected to the system. As they thought of their answers, scientists monitored changes in the system’s measurements to figure out whether the patient’s response was a yes or no.
The system did not decipher specific words. Instead, it measured oxygenation changes in specific areas of the brain, which lead to different mental states for yes or no responses. Initially, researchers asked patients simple questions with known answers. Once the patients were trained on how to answer the questions, researchers began asking open questions that had no known answers such as “Are you happy?”
Why patients gave wrong answers sometimes
With direct input from the family members of patients, Birbaumer and his colleagues constructed a total of 200 known questions and 40 open questions. The patients responded correctly at least 70% of the time. One patient was asked whether he would allow his daughter to marry her boyfriend. He said no nine out of ten times. Researchers said one patient had been using the system regularly.
When asked why patients would sometimes give wrong answers, Birbaumer surmised it could be because they often fall asleep. Some patients were partially blind, so they had a short attention span. In the future, scientists plan to develop a system that would allow patients to select words and letters with their brains.