Neuroimaging methods of consciousness assessment more directly evaluate brain function by observing neural responses to verbal command, according to a study in Scientific Reports.
This study consisted of a conceptual replication of a previous study that demonstrated evidence of command following in healthy controls and minimally conscious participants, but not unresponsive wakeful patients. The original results revealed that both minimally conscious and most unresponsive wakeful patients generated mismatch negativity (MMN) or P3a, referred to as a local effect to simple tone changes. Only minimally conscious participants generated a P3b, referred to as a global effect to changes in auditory patterns.
This follow-up reported the MMN, P3a and P3b responses to auditory tone and pattern changes from young, healthy controls (n=17), responsive hospice patients (n=8), and unresponsive actively dying hospice patients (n=5).
Consistent with controls and responsive participants, all five unresponsive patients showed some evidence of either early fronto-central negativity (MMN) or a later fronto-central positivity (P3a) or both, to tone changes. None showed a centro-parietal positivity (P3b) to tone changes.
These results and others reported in this study, support the theory that hearing is one of the last senses to go when patients are dying. Loved ones should keep talking to a dying relative for as long as possible.