I expect what you expect: An electrophysiological study on social expectation of pain

Pain and Disability Following Exercise-Induced Injury in Prognostic and Intervention Studies: The Why May Be More Important Than the How

OBJECTIVES

In preclinical prognostic studies, the description of expected outcomes during an informed consent process indicates that the extent of pain and disability experienced and recovery time is unknown. In intervention studies, the consent process suggests that pain and disability will definitely occur and a treatment provided. Our objective was to determine whether study design (prognosis or intervention) was associated with the severity of pain intensity and disability reports from a preclinical model.

MATERIALS AND METHODS

We pooled pain and disability outcomes from prognostic and intervention studies using an exercise-induced muscle injury model of pain. Pain intensity, disability, and fear of pain were collected by validated self-report measures. Pain and disability data were z-transformed for pooled analyses and compared across the study design.

RESULTS

Data from 310 people were included. The primary findings were that self-reported pain intensity and disability were: (1) higher in prognostic studies than in the intervention studies and (2) associated with fear of pain. A secondary finding was that fear of pain was lower in the intervention compared with the prognostic studies.

DISCUSSION

Although there are other possible explanations, we speculate that these results could be related to the uncertainty inherent to providing informed consent for a prognostic study. In light of these findings, we recommend that informed consent language be more carefully considered when pain is induced in a controlled manner. Incorporating informed consent language commonly used in prognostic studies could result in higher pain intensity and disability ratings in studies that use preclinical models to test the efficacy of pain interventions.

Behavioral Analysis of EEG Signals in Loss-Gain Decision-Making Experiments

Extraction and analysis of the EEG (electroencephalograph) information features generated during behavioral decision-making can provide a better understanding of the state of mind. Previous studies have focused more on the brainwave features after behavioral decision-making. In fact, the EEG before decision-making is more worthy of our attention. In this study, we introduce a new index based on the reaction time of subjects before decision-making, called the Prestimulus Time (PT), which have important reference value for the study of cognitive function, neurological diseases, and other fields. In our experiments, we use a wearable EEG feature signal acquisition device and a systematic reward and punishment experiment to obtain the EEG features before and after behavioral decision-making. The experimental results show that the EEG generated after behavioral decision due to loss is more intense than that generated by gain in the medial frontal cortex (MFC). In addition, different characteristics of EEG signals are generated prior to behavioral decisions because people have different expectations of the outcome. It will produce more significant negative-polarity event-related potential (ERP) in the forebrain area when the humans are optimistic about the outcomes.

The Role of the Observers' Perception of a Model's Self-Confidence in Observationally Induced Placebo Analgesia

The aim of this study was to investigate the effect of a model's self-confidence as well as the observer's self-esteem and self-efficacy on observationally acquired placebo analgesia. In addition, we aimed to verify the stability of the placebo effect induced by observational learning. Participants (n = 60) were randomly assigned to one of three groups: a self-confident model, an unself-confident model, and a control group. In the experimental groups, participants watched a videotaped model who rated the intensity of electrocutaneous pain stimuli applied in the placebo condition as lower than those applied in the non-placebo condition. The different levels of self-confidence in these groups were manifested in the body posture and facial expressions of the model as well as in specific behavior that accompanied the assessment of pain. Then, 16 electrocutaneous pain stimuli of the same intensity, preceded by the placebo or non-placebo, were applied to participants. In both experimental groups, in contrast to the control group, participants experienced less pain in the placebo than in the non-placebo condition. Although the magnitude of placebo analgesia did not differ between the experimental groups, multiple regression analysis revealed that the perceived self-confidence of the model, but not the self-efficacy or self-esteem of the observer, was a significant predictor of the placebo effect. Moreover, placebo analgesia induced by observational learning did not extinguish over the course of the experiment. These results support the premise that the observers' perception of a model's self-confidence plays a significant role in placebo effects. PERSPECTIVE: The results of this study open the discussion on the role of model's features in the effectiveness of observational learning in the induction of placebo effects. The study provides the very first suggestion that the perceived self-confidence of the model may be related to the magnitude of the observationally induced placebo analgesia. It suggests that self-confidence of other patients and medical staff might affect individual pain experiences.