In search of conditioned pain: an experimental analysis.

ABSTRACT: There is an ongoing debate about whether pain can be classically conditioned, but surprisingly, evidence is scarce. Here, we report 3 experiments investigating this idea. In a virtual reality task, healthy participants were approached and touched near or on their hand with a coloured pen (blue or yellow). During acquisition, participants learned that one of the colours of the pen (CS+) was predictive of a painful electrocutaneous stimulus (ECS) whereas the other coloured pen (CS-) was not. During the test phase, more frequent reports of experiencing an US when none was delivered ("false alarm") for the CS+ vs CS- qualified as evidence of conditioned pain. Notable differences between experiments were that the US was delivered when the pen touched a spot between the thumb and index finger (experiment 1; n = 23), when it virtually touched the hand (experiment 2; n = 28) and when participants were informed that the pen caused pain rather than simply predicting something (experiment 3; n = 21). The conditioning procedure proved successful in all 3 experiments: Self-reported fear, attention, pain, fear, and US expectancy were higher ( P < 0.0005) for the CS+ than the CS-. There was no evidence for conditioned pain in experiment 1, but there was some evidence in experiments 2 and 3. Our findings indicate that conditioned pain may exist, albeit most likely in rare cases or under specific situations. More research is needed to understand the specific conditions under which conditioned pain exists and the underlying processes (eg, response bias).

Boosting long-term effects of degraded memories via acute stress.

Combining recall of an emotional memory with simultaneous horizontal eye movements (i.e., Recall + EM) reduces memory aversiveness. However, the long-term persistence of this effect is inconsistent across studies. Given that stress may aid in the consolidation of memories, we examined whether acute stress can boost the long-term effects of degraded memories. To test this, participants recalled two negative memories, which were assigned to a Recall + EM or Recall Only condition. Before and after each intervention they rated memory aversiveness (i.e., immediate effects) followed by a stress-induction or control procedure. After a 24h-period, participants rated each memory again (i.e., long-term effects). We found that Recall + EM produces immediate effects but that these effects dissolve over time. Moreover, acute stress did not boost potential long-term effects of Recall + EM. Degraded memories were not retained better by applying stress. We discuss these results and how long-term effectiveness may still be achieved.

Overgeneralization of fear, but not avoidance, following acute stress.

Research has demonstrated the spreading of fear from threat-related stimuli to perceptually similar, but innocuous, stimuli. Less is known, however, about the generalization of avoidance behavior. Given that stress is known to affect learning and memory, we were interested in the effect of acute stress on (over)generalization of fear and avoidance responses. On the first day, one geometrical shape was paired with a mild electrical stimulus (CS+), whereas another shape was not (CS-). One day later, after participants had been exposed to the Maastricht Acute Stress Test or a control task, generalization of avoidance responses and fear (shock expectancy and skin conductance responses) was tested to a range of perceptual generalization stimuli. Generalization gradients were observed across different outcome measures. Stress enhanced generalization of shock expectancy to the stimulus most similar to the CS+. Our findings confirm that stress can affect the generalization of fear, but further studies are warranted.

On EMDR: Measuring the working memory taxation of various types of eye (non-)movement conditions.

BACKGROUND AND OBJECTIVE: A recent, large randomized controlled trial employing different forms of eye (non-)movements in eye movement desensitization and reprocessing (EMDR) showed that fixating the eyes either on a therapist's moving or non-moving hand led to equal reductions in symptoms of post-traumatic stress disorder (PTSD). However, numerous EMDR lab analogue studies found that eye movements produce larger memory effects than eyes stationary. These beneficial effects are typically explained by differences in working memory (WM) taxation. We tested the degree of WM taxation of several eye (non-)movement conditions used in the clinical trial. METHODS: All participants (N = 40) performed: (1) eyes moving by following the experimenter's moving finger, (2) eyes fixed on the experimenter's stationary finger, (3) eyes closed, or (4) looking unfocused into the room. Simultaneously they performed a simple reaction time task. Reaction times are an objective index of the extent to which different dual attention tasks tax WM. RESULTS: Eyes moving is more taxing than eyes fixed, while eyes fixed did not differ from eyes unfocused. All conditions were more taxing than eyes closed. LIMITATIONS: We studied WM taxation in a laboratory setting; no clinical interventions were applied. CONCLUSIONS: In line with previous lab studies, making eye movements was more taxing than eyes fixed. We discuss why this effect was not observed for reductions in PTSD symptoms in the clinical trial (e.g., differences in dependent variables, sample population, and intervention duration). For more comprehensive future insights, we recommend integration of mechanistically focused lab analogue studies and patient-oriented clinical studies.

Reduced return of threat expectancy after counterconditioning verus extinction.

Exposure-based therapies are effective for anxiety disorders, but relapse remains a problem. One explanation might be that exposure therapy reduces threat expectancy but not related feelings of unpleasantness (negative valence of the conditioned stimulus; CS+), which may promote return of threat expectancy and associated fear. Laboratory research has indeed shown that fear extinction leaves negative valence of the conditioned stimulus (CS+) intact. Here, we tested whether adding positive consequences to the CS+ during extinction, a procedure known as counterconditioning, would change the valence of the CS+ and thereby prevent return of threat expectancy. Participants underwent Acquisition (day 1), Intervention (counterconditioning or extinction; day 2), and Spontaneous recovery and Reinstatement (day 3). As expected, threat expectancy ratings during the Spontaneous recovery and Reinstatement tests were lower after counterconditioning than after extinction, but counterconditioning did not reduce CS + negative valence more than extinction. Alternative mechanisms and clinical implications are discussed.