locked-in syndrome
a condition in which a person cannot speak or move but is fully cognizant and aware of his or her surroundings. The individual has normal metabolic functions and sleep–wake cycles but is able to communicate only with eye movements (e.g., blinking, looking up or down). Electrical activity of the brain (including event-related potentials) generally is normal as well, as demonstrated through electroencephalography, single photon emission computed tomography, and other imaging techniques. Locked-in syndrome is poorly understood and frequently misdiagnosed as coma or a vegetative state; research suggests that physicians fail to recognize signs of consciousness in more than half of cases. It is associated with disruption of motor neurons in the brainstem—typically the pons—from hemorrhage, occlusion or infarction, traumatic brain injury, tumor, encephalitis, neuromuscular disorders (e.g., amyotrophic lateral sclerosis, Guillain-Barré syndrome), and other causes. Life expectancy of an individual with locked-in syndrome may be several decades with appropriate medical care, but the probability of significant motor recovery is small. See also brain–computer interface. [term coined in 1966 by U.S. neurologists Fred Plum (1924–2010) and Jerome B. Posner]