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Sickness behavior is a coordinated set of adaptive behavioral changes that develop in ill individuals during the course of an infection. They usually (but not necessarily) accompany fever and aid survival. Such illness responses include lethargy, depression, anxiety, loss of appetite, sleepiness, hyperalgesia, reduction in grooming〔 and failure to concentrate. Sickness behavior is a motivational state that reorganizes the organism's priorities to cope with infectious pathogens.〔 It has been suggested as relevant to understanding depression, and some aspects of the suffering that occurs in cancer. ==History== Sick animals have long been recognized by farmers as having different behavior. Initially it was thought that this was due to physical weakness that resulted from diverting energy to the body processes needed to fight infection. However, in the 1960s, it was shown that animals produced a blood-carried ‘‘factor X’’ that acted upon the brain to cause sickness behavior.〔Miller, N. (1964) "Some psychophysiological studies of motivation and of the behavioral effects of illness". Bull. Br. Psychol. Soc. 17: 1-20〕 In 1987, Benjamin L. Hart brought together a variety of research findings that argued for them being survival adaptations that if prevented would disadvantage an animal’s ability to fight infection. In the 1980s, the blood-borne factor was shown to be proinflammatory cytokines produced by activated leukocytes in the immune system in response to lipopolysaccharides (a cell wall component of Gram-negative bacteria). These cytokines acted by various humoral and nerve routes upon the hypothalamus and other areas of the brain. Further research showed that the brain can also learn to control the various components of sickness behavior independently of immune activation.. In 2015, Shakhar and Shakhar 〔(Shakhar K, Shakhar G. Why Do We Feel Sick When Infected-Can Altruism Play a Role? PLoS Biol. 2015 Oct 16;13(10):e1002276. doi: 10.1371/journal.pbio.1002276. eCollection 2015 Oct. PubMed PMID 26474156. )〕 suggested instead that sickness behavior developed primarily because it protected the kin of infected animals from transmissible diseases. According to this theory, termed the Eyam hypothesis, after the English Parish of Eyam, sickness behavior protects the social group of infected individuals by limiting their direct contacts, preventing them from contaminating the environment, and broadcasting their health status. Kin selection would help promote such behaviors through evolution. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sickness behavior」の詳細全文を読む スポンサード リンク
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