Different technical means are being developed aimed at communicating with brain-damaged patients with residual consciousness. This would allow them to express their thoughts, their emotions and their desires. On 5 August 2013, German, American, Australian and Belgian scientists (Camille Chatelle and Steven Laureys, from the Coma Science Group) described a simple and original means of communication in Current Biology(1): pupil dilation.

Any mental effort leads to an increase in the pupil’s diameter. Hence the researchers’ question: couldn’t we take advantage of this phenomenon to communicate with people who are physically incapable of interacting with their environment, such as patients with locked-in syndrome? “The idea was to ask healthy volunteers and brain-damaged subjects simple questions (“Is your name Frank?”, etc.) and ask them to calculate a relatively difficult mental arithmetic problem (17x42, for instance) if they wanted to reply affirmatively, or otherwise not do this calculation”, explains Steven Laureys. “As confirmation, we then asked them to do a similar calculation if they wanted to reply negatively.”

It wasn't the accuracy of the calculation carried out that was important – the brain-damaged patients were incapable of communicating the result anyway -, but whether the test participants had or had not accomplished a mental effort likely to make the pupils dilate. “In the healthy volunteers, the test proved to be convincing in all cases; in patients with locked-in syndrome, only two in five times”, the director of the Coma Science Group specifies. Why? “Undoubtedly because they were in a less adapted environment than a laboratory, because they were taking medication and their vigilance and level of attention sometimes fluctuated.”

A similar experiment was successfully performed on a patient in a minimally conscious state, not with the goal of conversing with them but, more prosaically, to determine whether it was possible to confirm they had residual consciousness by measuring pupil dilation.

For the time being, the technique used requires a camera and relatively extensive analytical means. “We’re thinking of developing an integrated system that is cheaper and easier to use”, says Steven Laureys. Studies are under way.

In patients suffering from classic LIS, the most frequent type, vertical ocular movements and/or blinking is preserved. These residual motor faculties serve as a means of communication for these subjects. However, the measurement of pupil dilation, which is slower, doesn’t hold much of a future for them. On the other hand, for other patients, it may be a major step towards a method of communication.