In "Locked inside" (SN: 8/8/15, p. 18), Laura Beil relates the story of a man who, before regaining the ability to move and communicate with his eyes, lived for 12 years mentally aware but unable to interact. "Scientists assume that stories like these, astonishing as they are, represent only a small fraction of patients," Beil wrote in her story exploring how scientists are learning to communicate with locked-in patients.
Brian Quass took issue with the assumption about the low fraction. "For scientists to claim that such incidents are rare at this early point in the investigation (after all, locked-in syndrome has scarcely been discovered) strikes me as a mixture of defensiveness and wishful thinking," he wrote.
Neuroscientist Damien Gabriel of the University Hospital of Besancon in France replies that there are "strong clues" that most vegetative patients are not conscious, including that many patients lack even elementary reflexes. "In this case, chances of having preserved cognitive abilities are extremely poor," he says.
Another indicator is the severity of brain damage. "More than half of the brain is sometimes missing," he says. Neuroscientist Srivas Chennu of the University of Cambridge agrees that science still has a lot to learn about vegetative patients: "Exactly which parts and functions of the brain are important for consciousness is indeed a fascinating question, and a topic of current research."