The placebo effect is a learning phenomenon strongly associated with cognitive mechanisms. Placebo conditioning, particularly, combines threat learning with verbal instructions and expectations....Show moreThe placebo effect is a learning phenomenon strongly associated with cognitive mechanisms. Placebo conditioning, particularly, combines threat learning with verbal instructions and expectations. These processes are central in shaping subjective pain experience and threat-related episodic memory. However, the specific influence of placebo conditioning on episodic memory accuracy and generalization is not yet known. It is hypothesized that threat associations enhance memory recognition and generalization by increasing arousal; thus, introducing a placebo manipulation in a threat conditioning paradigm might impair memory recognition by decreasing arousal. This can offer insights into the broader clinical implications of placebo, as threat-related responses and memory bias are hallmarks of anxiety disorders. This study used a within subjects experimental design with 72 healthy participants undergoing a pain calibration/placebo conditioning procedure, a Pavlovian threat conditioning paradigm with a placebo manipulation using pictures, and a memory test. Participants completed pain, mnemonic, and confidence ratings. We predicted that the placebo condition would correlate with lower subjective pain experience, and the CS+ condition with increased recognition memory and generalization compared to the CS+ placebo and CS- conditions. Although the placebo manipulation was successful, it did not significantly affect memory recognition, generalization or discrimination. There were indications that the CS+ condition correlated with higher recognition compared to the CS- condition, but these should be interpreted with caution. We conclude that the placebo manipulation’s subtle effects may not have reached the necessary threshold of arousal and motivational engagement required to alter memory processes. Limitations and suggestions for future research are discussed.Show less
Psychological research has mostly been focused on finding an explanation for behavior, rather than on finding a model that accurately predicts behavior. This approach often results in the use of...Show morePsychological research has mostly been focused on finding an explanation for behavior, rather than on finding a model that accurately predicts behavior. This approach often results in the use of models that fit very well to the sample used for testing but are difficult to generalize to new samples. Similarly, models are often too complex and take into consideration too many variables. Classically, replications would be performed to account for these issues. This is however an expensive, time-consuming, and laborious process, leading to the perpetuation of nonreplicated studies in psychology. This thesis presents a possible solution stemming from the field of machine learning, namely using cross-validation. With cross-validation, the predictive performance of a model can be assessed using only one dataset. This thesis examined the use of cross-validation by applying it over an existing dataset and comparing its output to the output of conventional null-hypothesis testing. The results show that using cross-validation reduces the likelihood of making overly optimistic claims, by reducing the chances of using excessively complex models unable to generalize to new samples. Furthermore, cross-validation gives the opportunity to examine the predictability of models while preserving the explanatory power. It therefore proves to be a useful tool in the field of psychological research.Show less
Nocebo effects are harmful treatment effects of an inert agent elicited by the anticipation of negative effects. Limited amount of studies focused on nocebo effects on pain, suggesting nocebo...Show moreNocebo effects are harmful treatment effects of an inert agent elicited by the anticipation of negative effects. Limited amount of studies focused on nocebo effects on pain, suggesting nocebo effects can increase pain sensations. Importantly, a better understanding of nocebo effects in relation to pain is needed due to its clinical relevance. Few studies showed that established nocebo effects can generalize to different stimuli, yet it has not been investigated that nocebo effects can occur from one modality to another within the category of pain sensations. Besides, research suggests personality factors such as anxiety can play a role in these nocebo effects. This study investigates nocebo effects on heat pain, its generalization to different pain stimuli, and as an explorative objective, we investigate the possible moderating role of anxiety in these effects. At first, the STAI-S questionnaire was assessed to measure the levels of anxiety per individual. To induce negative expectations, two nocebo inducing mechanisms were used; first, a conditioning phase related to heat pain was used to acquire an association between the activation of a sham device (ENS) and increased pain stimulation, secondly, verbal suggestion was used by informing participants the ENS will increase pain sensations. Then, heat pain stimuli set at the same temperature were assessed with the supposed activation and deactivation of the ENS. Thereafter, pressure pain stimuli at the same pressure were administered with the supposed activation/deactivation of the ENS. The results showed that participants experienced more heat pain and pressure pain with the supposed activation of the ENS. This demonstrates significant nocebo effect for heat pain, and it shows nocebo effects significantly generalized to pressure pain stimuli. However, for the explorative outcome, the moderation analysis did not find indications that anxiety played a role in these effects. The current findings suggests the important role of negative expectations interfering with pain perception and altering the experience of different pain stimuli. We discuss the importance to understand the less researched nocebo phenomenon and its generalization to effectively reduce nocebo effects in a clinical setting. Also, the need to explore psychological factors in these nocebo effects is emphasized.Show less
