“…Fear and anxiety responses are organized at different levels in a putative rostro-caudal hierarchical circuitry for defense reactions (McNaughton & Corr, 2004); therefore, we predict that direct exposure to threatening stimuli should induce high levels of fear and arousal and inhibit pain, whereas exposure to diffuse or potentially threatening stimuli (e.g., novelty) induce a state of anxiety and enhance pain (Rhudy & Meagher, 2000). Aside from anxiety and fear, stressful stimuli that do not produce fear but induce neuroendocrine responses (e.g., restraint stress, social isolation, and forced swimming) can induce analgesia (Bodnar, Glusman, Brutus, Spiaggia, & Kelly, 1979;Bodnar, Kelly, Spiaggia, Ehrenberg, & Glusman, 1978;Bodnar, Merrigan, & Sperber, 1983;Costa, Smeraldi, Tassorelli, Greco, & Nappi, 2005;Puglisi-Allegra & Oliverio, 1983), an effect that is mediated by hypothalamicpituitary-adrenal axis hormones (Butler & Finn, 2009).…”