Although dysregulation of the cholinergic system and oxidative stress have been the promising hypothesis for explaining the pathogenesis of POCD and delirium, increased inflammation still plays an important part in explaining the development of neurocognitive disorders, of which increased level of pro-inflammatory cytokines, such as TNF-α IL-1β, IL-18, and IL-6, can be observed in the brain and blood samples of patients with dementia, delirium, and POCD39–41. This evidence concerns the gene IL18 and delirium.