Diagnosis of patients with a disorder of consciousness is very challenging. 
Previous studies investigating resting state networks demonstrate that 2 main 
features of the so-called default mode network (DMN), metabolism and functional 
connectivity, are impaired in patients with a disorder of consciousness. 
However, task-induced deactivation--a third main feature of the DMN--has not 
been explored in a group of patients. Deactivation of the DMN is supposed to 
reflect interruptions of introspective processes. Seventeen patients with 
unresponsive wakefulness syndrome (UWS, former vegetative state), 8 patients in 
minimally conscious state (MCS), and 25 healthy controls were investigated with 
functional magnetic resonance imaging during a passive sentence listening task. 
Results show that deactivation in medial regions is reduced in MCS and absent in 
UWS patients compared to healthy controls. Moreover, behavioral scores assessing 
the level of consciousness correlate with deactivation in patients. On 
single-subject level, all control subjects but only 2 patients in MCS and 6 with 
UWS exposed deactivation. Interestingly, all patients who deactivated during 
speech processing (except for one) showed activation in left frontal regions 
which are associated with conscious processing. Our results indicate that 
deactivation of the DMN can be associated with the level of consciousness by 
selecting those who are able to interrupt ongoing introspective processes. In 
consequence, deactivation of the DMN may function as a marker of consciousness.