Locked-in syndrome is a dramatic condition where, after brain stem damage, patients are conscious but paralysed and can only communicate with the outside world by an eye-blink or muscle twitch.
Because of limited communication it has been difficult to assess the impact of the damage on thinking and reasoning, but a French team have created tests that can be completed by simple yes / no movements – allowing the first comprehensive study into the cognition of the locked-in mind.
The syndrome usually occurs after a stroke, where an interruption to the blood supply selectively damages the neurological ‘relay station’ that transmits movement impulses to the rest of the body, leaving an almost total paralysis – classically except for a facial muscle.
It has been assumed that affected people are paralysed but cognitively intact – their thinking isn’t affected.
In one famous example, the editor of Elle magazine, Jean Dominique Bauby, wrote the book The Diving Bell and the Butterfly after suffering locked-in syndrome by painstakingly selecting letters with an eye-blink. It’s both stunningly beautiful and eloquent, demonstrating a keen and focused mind.
But because of extremely limited communication, it’s difficult to say whether this level of preserved mental ability is common because traditional neuropsychological tests usually require relatively complex responses.
To address the problem, a French team, led by neurologist Marc Rousseaux, designed tests to assess nine patients that included everything from visual recognition tasks to logical-mathematical reasoning problems, all which could be answered with yes / no responses – just eye-blinks in some cases.
The appendix of their article has the full list of the tests and they are remarkable for their ingenious design.
They team found that while the patients were generally mentally sharp, problems in particular areas were not uncommon, with a significant minority showing selective impairments in areas such as comprehension, understanding meaningful connections, or problem solving.
Sadly, this means that it is unlikely that all locked-in patients share Jean-Dominique Bauby’s remarkably preserved intellect, but the development of these ingenious tests means that we can better understand the impact of the syndrome, and the strengths and weakness of affected patients.
Link to full-text of study on locked-in patients.