Severe head injury or brain injury presents clinical neuroscientists with a unique challenge. Based on an objective assessment of cognitive and neurological function, it is sometimes hard to recognize our patients as members of our moral community (actually or potentially) but we treat them as if that were is the case, and, therefore, as if they need rescuing. Thus their existences as enigmata—beings who may or may not reveal themselves to us through social and personal function realized in conversations and relationships—are in doubt. However, the objective mode of assessing individuals and their mental functions needs to be bracketed here, as we reconnect with them and offer them our help in the restorative journey that they need to take. The journey has many tortuous paths comprising it, not the least of which is the existential question of whether the damaged human being with whom we are engaged actually can be restored to a meaningful life. A negative answer to that question can bring the whole process to an abrupt end. Neuroscience cannot answer some of these questions, as they are ethical. Is this a life worth living and are our commitments going to go the distance that must be traversed here. Therefore, this is an area where ethics take priority over neuroscience, and it is on our ethical response that everything else hinges. Understanding the light this throws on the nature of a human being takes us to the heart of the value of every human being and the nexus of mutuality that is the moral community.

Low vitamin B12 status is common in older people; however, its public health significance in terms of neurological manifestations remains unclear. The present systematic review evaluated the association of vitamin B12 status with neurological function and clinically relevant neurological outcomes in adults aged 50+ years. A systematic search of nine bibliographic databases (up to March 2013) identified twelve published articles describing two longitudinal and ten cross-sectional analyses. The included study populations ranged in size (n 28–2287) and mean/median age (range 65–81 years). Studies reported various neurological outcomes: nerve function; clinically measured signs and symptoms of nerve function; self-reported neurological symptoms. Studies were assessed for risk of bias, and results were synthesised qualitatively. Among the general population groups of older people, one longitudinal study reported no association, and four of seven cross-sectional studies reported limited evidence of an association of vitamin B12 status with some, but not all, neurological outcomes. Among groups with clinical and/or biochemical evidence of low vitamin B12 status, one longitudinal study reported an association of vitamin B12 status with some, but not all, neurological outcomes and three cross-sectional analyses reported no association. Overall, there is limited evidence from observational studies to suggest an association of vitamin B12 status with neurological function in older people. The heterogeneity and quality of the evidence base preclude more definitive conclusions, and further high-quality research is needed to better inform understanding of public health significance in terms of neurological function of vitamin B12 status in older people.