Expectancy is one of the cognitive processes that influence pain perception and bias nociceptive processing in brain.In spite of numerous human studies on pain expectation,animal models are important tools for investigating the neural mechanisms underlying the cognitive modulation of pain.Very few animal models are available on pain anticipation due to the inability of animals to rate the subjective experience.Thus,a more reasonable model of pain expectation is needed for animal studies.To delineate the process of expectation about pain as well as the effects of expectation on pain in animals,we hereby intent to establish an animal model in which the differential components can be isolated after pain-related learning.A novel balanced crossover design was used in the present study to assess the pain cue-based expectancy and its effects on nociceptive behaviors in rats.The promising method for addressing these issues is the utilization of the crossover design that commonly used in human disciplines.On the basis of tone-laser paired trace conditioning paradigm,a series of tasks were conducted from simple conditioning to more difficult signal discrimination task in rats.Four components relating to pain expectation,i.e.,expectancy-based pain,expectancy of pain,pain,and normal state,were successfully isolated.A series of pain-related conditioning task with increasing cognitive load brought about significant voluntary withdrawal behaviors in response to pain predictive cues.The current study provided a useful animal model of pain expectation,which will be instrumental in further understanding of the neural basis of expectation-based modulation at cellular and molecular levels.