We only include the measurement of brain levels of IL-6, but not other pro-inflammatory cytokines, in the present studies because there are sufficient literatures suggesting the association between IL-6 and postoperative delirium in patients [45–49], and our previous studies demonstrating that the anesthesia/surgery caused age-dependent increase in blood IL-6 levels in the mice [50]. This evidence concerns the gene IL6 and delirium.