Severe brain injuries can lead to a vegetative or minimally conscious state, in which conscious awareness is disrupted. Severe brain injuries can also lead to locked-in syndrome, a state in which a person is fully conscious but completely unable to respond. Clinical assessment of these disorders is difficult because the measurement of arousal and motor reaction is subjective, and prone to slight variations. Misdiagnosis is not uncommon.
More objective measures of consciousness, such as functional MRI (fMRI), can more accurately detect these slight variations in arousal and consciousness. A recent fMRI study analyzed differences in how well the brain connected one hemisphere to another while in a resting state. The study compared healthy people to those who were diagnosed with a disorder of consciousness. In most cases, lower levels of brain connectivity correlated with lower levels of consciousness. However, three patients showed levels of brain connectivity that were comparable to healthy people. One of these patients had locked-in syndrome, and the other unexpectedly recovered consciousness.
The analysis of brain connectivity at a resting state may therefore be a more accurate tool for both diagnosis and prediction of recovery.
Ovadia-Caro S. Nir Y, Soddu A, et al. Reduction in inter-hemispheric connectivity in disorders of consciousness. PLOS One. (June 2012).