Locked-in syndrome, the condition of total paralysis while conscious, may be caused by traumatic brain injury, stroke, or overdose. Some patients can communicate with eye movements or blinks, but others are rendered effectively silent.
Neurophysicist Wolfgang Einhäuser-Treyer of Philipps-Universität in Marburg, Germany, and his research team sought to develop a communication system for all locked-in patients, one that requires no voluntary muscle control whatsoever. They focused on involuntary eye responses, and specifically on a person’s pupils, which are known to dilate according to the amount of mental effort expended to complete a task.
A patient is asked a factual question, such as, “Are you 20 years old?” A computer intones yes and then no, and each yes or no is accompanied by a difficult mental math problem, exclusive to that word, shown on a screen. The patient is asked to solve the problem that corresponds to the right answer while ignoring the problem that corresponds to the wrong answer. A bedside camera records the size of the patients’ pupils over time.
Tested on locked-in patients in France, the system achieved an accuracy rate of up to 90 percent, meaning that the system worked 90 percent of the time: patients were able to communicate yes or no by expending mental effort on the corresponding math puzzle. Results were published in Current Biology.
The researchers hope the system will become widely adopted by physicians. Meanwhile, Einhäuser-Treyer is working on ways to make pupil-dilation measurement useful as a diagnostic tool for a wider group of patients, used in tandem with such tools as electroencephalography, the recording of electrical activity along the scalp.
