Despite being widely assumed, the worsening impact of unpredictability on pain perception remains unclear because of conflicting empirical evidence, and a lack of systematic integration of past research findings. To fill this gap, we conducted a systematic review and meta-analysis focusing on the effect of unpredictability on pain perception. We also conducted meta-regression analyses to examine the moderating effect of several moderators associated with pain and unpredictability: stimulus duration, calibrated stimulus pain intensity, pain intensity expectation, controllability, anticipation delay, state and trait negative affectivity, sex/gender and age of the participants, type of unpredictability (intensity, onset, duration, location), and method of pain induction (thermal, electrical, mechanical pressure, mechanical distention). We included 73 experimental studies with adult volunteers manipulating the (un)predictability of painful stimuli and measuring perceived pain intensity and pain unpleasantness in predictable and unpredictable contexts. Because there are insufficient studies with patients, we focused on healthy volunteers. Our results did not reveal any effect of unpredictability on pain perception. However, several significant moderators were found, ie, targeted stimulus pain intensity, expected pain intensity, and state negative affectivity. Trait negative affectivity and uncontrollability showed no significant effect, presumably because of the low number of included studies. Thus, further investigation is necessary to clearly determine their role in unpredictable pain perception.

中文翻译：

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不可预测性对疼痛感知的影响：系统评价和荟萃分析。

尽管人们普遍认为，不可预测性对疼痛感知的日益恶化的影响仍不清楚，因为经验证据相互矛盾，而且缺乏对过去研究结果的系统整合。为了填补这一空白，我们进行了系统回顾和荟萃分析，重点关注不可预测性对疼痛感知的影响。我们还进行了荟萃回归分析，以检验与疼痛和不可预测性相关的几个调节因素的调节作用：刺激持续时间、校准刺激疼痛强度、疼痛强度预期、可控性、预期延迟、状态和特质负面情感、性别和年龄。参与者、不可预测性的类型（强度、发作、持续时间、位置）以及疼痛诱导方法（热、电、机械压力、机械膨胀）。我们纳入了 73 项实验研究，其中成年志愿者操纵疼痛刺激的（不可）预测性，并在可预测和不可预测的环境中测量感知的疼痛强度和疼痛不愉快程度。由于对患者的研究不足，我们将重点放在健康志愿者身上。我们的结果没有揭示不可预测性对疼痛感知的任何影响。然而，我们发现了几个重要的调节因素，即目标刺激疼痛强度、预期疼痛强度和状态负面情感。负面情感和不可控性特质没有显示出显着影响，可能是因为纳入的研究数量较少。因此，有必要进一步研究以明确确定它们在不可预测的疼痛感知中的作用。