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. Author manuscript; available in PMC: 2008 Feb 1.
Published in final edited form as: Brain Behav Immun. 2006 Nov 7;21(2):153–160. doi: 10.1016/j.bbi.2006.09.006

Figure 2.

Figure 2

Evolution of the concept of sickness behavior. This figure illustrates the different steps in formulation of the concept of cytokine-induced sickness behavior. It demonstrates that the concept was grounded initially in two different lines of research that focused on the possible aversive stimulus properties of immune activation on one hand and the metabolic constraints of the fever response on the other hand. Ultimately, the concept of cytokine-induced sickness behavior found its own momentum by borrowing from motivational theory. Whether this concept is sufficiently solid to encompass all aspects of the organism's response to stimulation of the innate immune system or must be included in another more basic motivational system, such as the pain defense system, is still disputed.