Department of Physiological and Clinical Psychology/Psychotherapy, University of Greifswald, Greifswald, Germany.
Department of Biological Psychology and Affective Science, Faculty of Human Sciences, University of Potsdam, Potsdam, Germany.
Psychophysiology. 2021 Jun;58(6):e13812. doi: 10.1111/psyp.13812. Epub 2021 Mar 24.
During fear conditioning, a cue (CS) signals an inevitable distal threat (US) and evokes a conditioned response that can be described as attentive immobility (freezing). The organism remains motionless and monitors the source of danger while startle responses are potentiated, indicating a state of defensive hypervigilance. Although in animals vagally mediated fear bradycardia is also reliably observed under such circumstances, results are mixed in human fear conditioning. Using a single-cue fear conditioning and extinction protocol, we tested cardiac reactivity and startle potentiation indexing low-level defensive strategies in a fear-conditioned (n = 40; paired presentations of CS and US) compared with a non-conditioned control group (n = 40; unpaired presentations of CS and US). Additionally, we assessed shock expectancy ratings on a trial-by-trial basis indexing declarative knowledge of the previous contingencies. Half of each group underwent extinction under sham or active transcutaneous vagus nerve stimulation (tVNS), serving as additional proof of concept. We found stronger cardiac deceleration during CS presentation in the fear learning relative to the control group. This learned fear bradycardia was positively correlated with conditioned startle potentiation but not with declarative knowledge of CS-US contingencies. TVNS abolished differences in heart rate changes between both groups and removed the significant correlation between late cardiac deceleration and startle potentiation in the fear learning group. Results suggest, fear-conditioned cues evoke attentive immobility in humans, characterized by cardiac deceleration and startle potentiation. Such defensive response pattern is elicited by cues predicting inevitable distal threat and resembles conditioned fear responses observed in rodents.
在恐惧条件反射中，线索 (CS) 预示着不可避免的远端威胁 (US)，并引发一种条件反应，可以被描述为警觉性不动 (冻结)。生物体保持不动，并监测危险的来源，同时惊跳反应被增强，表明处于防御性高度警惕状态。尽管在动物中，迷走神经介导的恐惧性心动过缓也在这种情况下可靠地观察到，但在人类恐惧条件反射中，结果是混合的。使用单一线索恐惧条件反射和消退协议，我们在恐惧条件反射组 (n = 40；CS 和 US 的配对呈现) 和非条件对照组 (n = 40；CS 和 US 的非配对呈现) 中测试了心脏反应性和惊跳增强，以指示低水平的防御策略。此外，我们在每次试验的基础上评估了对电击预期的评分，以指示对先前事件的陈述性知识。每组的一半接受假刺激或经皮迷走神经刺激 (tVNS) 的消退，作为额外的概念验证。我们发现，在恐惧学习中，CS 呈现时的心脏减速比对照组更强。这种习得性恐惧性心动过缓与条件性惊跳增强呈正相关，但与 CS-US 事件的陈述性知识无关。tVNS 消除了两组之间心率变化的差异，并消除了恐惧学习组中晚期心脏减速和惊跳增强之间的显著相关性。结果表明，恐惧条件反射的线索在人类中引起警觉性不动，表现为心脏减速和惊跳增强。这种防御性反应模式是由预测不可避免的远端威胁的线索引起的，类似于在啮齿动物中观察到的条件性恐惧反应。
