Next, fatigue and depression share some dimensions in the concept of sickness behavior, and there are indications that depression can be induced through the same inflammatory mechanisms that induce fatigue; increased concentrations of IL-1β are found in both the brains of mice with mild depression and the blood of humans with depression disorders (Goshen et al. 2008; Ellul et al. 2016). This evidence concerns the gene IL1B and major depressive disorder.