Conscious awareness in patients in vegetative states: myth or reality?

Do vegetative state (VS) and minimally conscious state (MCS) patients experience emotions and have conscious awareness of themselves and their surroundings? Can neuroimaging clarify these questions? Neuroimaging responses to stimuli are classified into four levels: level 0 indicates no response; level 1 indicates responses limited to the primary sensory cortices; level 2 indicates activation of primary sensory cortices and higher-order associative areas; level 3 indicates activation of cortical regions to either mental imagery tasks or high-level language stimuli requiring distinction of ambiguous from unambiguous words. Level 0 or level 1 was noted in 125 of 193 VS patients (65 %) and 46 of 121 MCS patients (38 %), suggesting no evidence of conscious awareness. Level 2 or level 3 was observed in 68 of 193 VS patients (35 %) and 75 of 121 MCS patients (62 %), indicating some cognitive processing. These data may denote the presence of conscious awareness or may simply identify neuronal processing without phenomenological awareness. The pro and cons of these conflicting interpretations are discussed.