Stress-induced sickness behaviors: An alternative hypothesis for responsesduring maternal separation

During maternal separation, some primate and nonprimate species show a biph asic (active/passive) response. The second stage is characterized by reduce d activity a hunched body posture, and other behaviors. Traditionally, the second stage has been referred to as "despair" and is considered an animal model for human depression. Recent research in psychoneuroimmunology sugges ts an alternative hypothesis-that behaviors occurring during the second pas sive phase represent stress-induced "sickness behaviors." This perspective more readily accounts for findings in widely divergent species', does not r equire assumptions regarding the ability to express complex emotional state s, is empirically testable, and aligns the separation model with recent hyp otheses regarding the nature and ontogeny of depressive illness. (C) 2001 J ohn Wiley & Sons, Inc.