People in a vegetative state, usually as a result of brain trauma or anoxia (lack of oxygen) by definition have no signs of conscious awareness or activity. The definition, therefore, is based largely on the absence of evidence for consciousness.
Of course, arguments based upon the absence of evidence are only as compelling as the degree to which evidence has been properly searched for. In recent years technology has advanced to the point that our ability to detect the possible subtle signs of consciousness in those presumed to be vegetative has increased – mainly through functional MRI scans (fMRI) and electroencephalograms (EEGs).
There has been a steady stream of studies demonstrating that a small minority of patients thought to be vegetative actually display some signs of minimal consciousness. The latest such study was recently published in Neuroimage: Clinical by a research team from the University of Cambridge.
But let’s back up a bit first. Even prior to evaluating vegetative patients with fMRI and advanced EEG techniques, several studies showed that a detailed neurological exam specifically designed to detect the most subtle clinical signs of consciousness could find such signs in some patients who were diagnosed as being vegetative by more standard neurological exam. According to one study as many as 41% of patients diagnosed as vegetative were really minimally conscious, meaning they had subtle signs of consciousness, but still cannot wake up, converse, or act purposefully. (more…)