Locked-in syndrome (LIS) is the harrowing condition that leaves fully conscious patients unable to communicate due to complete paralysis. Now, researchers have uncovered a new way to help victims of LIS communicate with the outside world — by measuring changes in the diameter of their pupils.
The eye has long been recognized as one of the most effective modes of communication at the disposal of patients suffering from LIS. Journalist Jean-Dominique Bauby (pictured below), who became trapped in his stock-still body following a massive stroke, famously took 10 months to write The Diving Bell and the Butterfly – a feat he accomplished with the aid of a transcriber by blinking his left eye to select letters from a French language frequency-ordered alphabet.
Still, not all victims of LIS retain full, conscious control of their eyes. There are other technologies available to aid in communication (EEG caps, for example) but the process is typically time-consuming, and the equipment itself expensive. Recently, neurophysicist Wolfgang Einhauser, who studies how pupils change size during decision-making, teamed up with Steven Laureys, a member of the Coma Science Group at the University Hospital of Liège in Belgium, in search of a simpler, more cost-effective way to help LIS victims reconnect with the outside world. The pair decided to explore the potential technical applications of a long-established link between mental engagement and pupil dilation (an observation first made in the early '60s) – only this time, their measurements would be aided by an affordable laptop and camera setup.
Healthy subjects were asked a yes-or-no question with one right answer, such as “Is your brother named Adam?” They watched a computer screen that displayed a math problem while announcing the response “Yes.” A few seconds later, it said “No” and showed a second problem. The subjects were asked to compute only the problem displayed with the correct answer and to ignore the other. A camera in front of their eyes measured precise changes in their pupils. It didn’t matter if they got the problem right, or if they completed it at all. Mental effort alone was enough to dilate their pupils and indicate which answer they chose, the team reports today in Current Biology. Einhäuser says that patients could use their pupils to respond to any question with two possible answers. The simple laptop and camera setup would cost less than $1000, he says.
Six healthy individuals and seven locked-in patients tried the new setup, answering a series of yes-or-no questions and computing the problem only for their chosen answer. The method had 84% to 99% success in reading the responses of healthy patients. Three of the seven paralyzed patients got better-than-chance results: The computer picked their intended answer between 67% and 84% of the time. Although far from perfect, these levels represent “very good accuracy,” according to Niels Birbaumer, a neurobiologist at the University of Tübingen in Germany who specializes in helping locked-in patients regain communication.
Einhauser and Laureys hope that, in time, their new technique will become increasingly useful not just as a communicative tool, but a diagnostic one.