Brain death and disorders of consciousness.

While often confused by non-medical specialists, brain death and disorders of consciousness such as coma, vegetative state, and minimally conscious state are clearly distinct and unambiguously distinguishable. Moreover, biological models underpin each category uniquely and with increasing precision. In this Primer, we frame the distinctions across the different conditions, point to recent work that advances measurements able to identify their differences, and explain two inter-related paradoxes. The first paradox is the brain dead patient whose 'phenotype' betrays the ultimate futility and lack of sustainability of the state. The second paradox is that of patients who retain apparent higher levels of cognitive function but who may be misidentified as remaining in a vegetative state or one of the similar conditions formulated in the recently defined syndrome of cognitive motor dissociation. Building on emerging data and models underlying each of these brain states, we place recent controversies over the assessment of brain dead patients into a scientific and wider societal context. We conclude by placing brain death into a broader conceptual framework that takes account of emerging scientific knowledge about disorders of consciousness.