A new class of consciousness
The past few years have seen the emergence of a controversial new category of impaired consciousness, the minimally conscious state (MCS). The term was first used in 2002 to describe people who previously would have been diagnosed as vegetative, but who can track movement with their eyes and may respond intermittently. Eelco Wijdicks of the Mayo Clinic describes MCS as "the most severe form of neurological disability in a conscious patient."22
Neurologists agree that it is vital to be able to distinguish between MCS and PVS in a patient, though many are still uncertain if MCS covers a single condition or a wide range of disorders. The diagnostic criteria are "difficult to define," says Wijdicks, "and the boundaries are uncertain (how minimal and how maximal?)."23
An estimated 100,000 Americans exist in this state of intermittent awareness, and some do recover fully. "It took years to get some agreement on the definition," says neurologist Nancy Childs of the Healthcare Rehabilitation Center in Austin, Texas, "and it's only now getting some acceptance, but we've known for years that there was this other group."24 In the early 1990s, studies designed by Dr. Childs and Dr. Keith Andrews of London's Royal Hospital for Neurodisability discovered signs of awareness in more than one-third of patients who had originally been diagnosed as vegetative.
Brain scans have figured highly in defining the new diagnosis. A landmark study by Joy Hirsch of Columbia University and Nicholas Schiff of Cornell University's Weill Medical College used fMRI scans of two minimally conscious patients to examine neural characteristics of the state. During the scan, the investigators played recordings of close family members talking about familiar events in the patients' lives.25 What Hirsch and Schiff found shocked them: The minimally conscious patients showed mental activity similar to healthy volunteers in response to the meaningful stories—though they showed less activity compared to healthy brains when narratives were played in reverse (and thus were linguistically meaningless).
"It was haunting,"26 Hirsch recalled when she discussed the findings. Results like these, though not ironclad proof of awareness, suggest that there may be cognitive life in patients who cannot respond to simple commands or communicate reliably.