Connectivity between Gut Microbiota and Terminal Awakenings in Alzheimer's Disease

Memory is empirically described as a brain function that connects the past to the present. This reductionist approach has focused on memory function within neurons and synapses, leading to an understanding that memory loss in dementia is caused by irreversible neuronal damage. However, recent palliative case reports and the Human Connectome Project have challenged the "irreversible" paradigm by indicating that some demented patients are able to retrieve supposed 'lost' memories and cognitive functions near death. The serotonin-centric hypothesis and the lifelong oligodendrocyte differentiation capacity may explain terminal awakening symptoms in these patients. Furthermore, an increased rate of serotonin-secreting and oligodendrocyte precursor cell-triggering gut bacteria near death temporally correlates with lucid improvements in demented patients. These findings may shift the context of terminal memory retrieval from a purely neuronal to a systemic idea that bridges terminal lucidity and gut microbiota. In this review, we take the systemic approach further and point out a temporal correlation between the gut microbiome and terminal lucid episodes in Alzheimer's patients.