Red induces hyperalgesia and white induces hypoalgesia regardless of pain modality.

Colors are an important factor that influences different aspects of people's lives. However, little is known about the effects of colors on pain. This preregistered study aimed to investigate whether the type of pain affects the impact of colors on pain intensity. 74 participants were randomly divided into 2 groups according to the type of pain: electrical or thermal. In both groups, pain stimuli of the same intensity were preceded by different colors. Participants rated the pain intensity induced by each pain stimulus. Additionally, pain expectations related to each color were rated at the beginning and the end of the procedure. A significant effect of color on pain intensity ratings was found. Pain was most intense in both groups after red, whereas the lowest ratings were given after white. A similar pattern of results was observed for pain expectations. Expectations also correlated with and were found to be a predictor of experienced pain for white, blue, and green. The study shows that white can reduce, while red can alter the experienced pain. Moreover, it shows that the effect of colors is affected to a greater extent by the pain expectations rather than the pain modality. We conclude that the way colors influence pain broadens the current knowledge on effects of colors on human behavior and could help in the future both patients and practitioners.

When one suffers less, all suffer less: Individual pain ratings are more effective than group ratings in producing placebo hypoalgesia.

BACKGROUND: Placebo hypoalgesia can be induced by observing a person (model) whose pain relief is the result of the use of an inert substance or procedure. This study examined whether verbal modelling, that is, showing pain ratings provided by other people, is sufficient to induce placebo hypoalgesia. METHODS: Participants from the experimental groups were acquainted with pain ratings (presented on VASs) derived from a single person (groups 1 and 3) or a group of people (groups 2 and 4) that were allegedly subjected to the same painful procedure. The ratings of pain stimuli that were allegedly applied with placebo were lower than the ratings of stimuli applied without placebo. In two of the experimental groups (group 3 and 4), participants also watched a video recording showing individuals who allegedly provided pain ratings; however, they did not observe them undergoing pain stimulation. The control group did not undergo any manipulation. Then, the participants received a series of the same thermal pain stimuli that were applied either with or without placebo and rated their intensity. RESULTS: Placebo hypoalgesia was induced only in participants presented with pain ratings provided by a single person, regardless of whether this person was previously seen. However, the pain ratings presented to the participants generally decreased individual pain sensations, regardless of whether they came from a group of people or a single person. CONCLUSIONS: Verbal modelling can produce placebo hypoalgesia and reduce pain sensations. It may be effectively used in clinical practice to modify patients' responses to pain treatment. SIGNIFICANCE: This study shows that knowledge about pain ratings provided by another person is sufficient to induce placebo hypoalgesia; thus, neither direct nor indirect observation of a person experiencing pain is necessary to induce this effect. Pain ratings derived from a group of people can decrease pain sensations but they do not produce placebo hypoalgesia.

Order does matter: the combined effects of classical conditioning and verbal suggestions on placebo hypoalgesia and nocebo hyperalgesia.

ABSTRACT: In most experimental studies in which verbal suggestion and classical conditioning are implemented together to induce placebo effects, the former precedes the latter. In naturally occurring situations, however, the information concerning pain does not always precede but often follows the pain experience. Moreover, this information is not always congruent with experience. This study investigates whether the chronology of verbal suggestion and conditioning, as well as their congruence, affects placebo hypoalgesia and nocebo hyperalgesia. The effects induced in 15 groups were compared. The participants in 8 experimental groups were presented with verbal suggestions that were either congruent or incongruent with classical conditioning. The verbal suggestions were provided either before or after conditioning. In 2 other experimental groups, placebo conditioning or nocebo conditioning was implemented without any verbal suggestion; in 2 groups, verbal suggestion of hypoalgesia or hyperalgesia without conditioning was applied. The control groups without any suggestions or conditioning were also included. Placebo hypoalgesia induced by congruent procedures was significantly stronger when the suggestion of hypoalgesia preceded rather than followed conditioning. The order of the congruent procedures did not affect the magnitude of nocebo hyperalgesia. In the groups in which incongruent procedures were implemented, placebo hypoalgesia or nocebo hyperalgesia was in line with the direction of the last-used procedure, regardless of whether it was conditioning or verbal suggestion. The results show that not the type of the procedure (verbal suggestion or conditioning), but the direction of the last-used procedure shapes pain-related expectancies and determines placebo effects.

One of us or one of them? The effects of the model's and observer's characteristics on placebo analgesia induced by observational learning.

Previous studies have proved that observational learning can induce placebo analgesia, but the factors that influence observationally induced placebo analgesia have not yet been extensively examined. The primary goal of this study was to investigate the effect of information about the role that the observed person (model) plays in the experiment on the magnitude of the observationally induced placebo effect. This study also examined the contribution of the observer's empathy, conformity and fear of pain to the placebo analgesia induced by observational learning. The effects induced in two experimental groups and one control group were compared. Participants in the experimental groups observed a model introduced as either another participant taking part in the study or a coworker of the experimenter. The model rated the intensity of pain induced by electrocutaneous stimuli preceded by color stimuli. One-half of all participants watched a model rating pain stimuli preceded by the color orange as higher than stimuli preceded by the color blue; for the other half, the ratings were the opposite. There was no observation in the control group. Subsequently, all participants received pain stimuli of the same intensity preceded by orange and blue stimuli and rated the intensity of the experienced pain. Placebo analgesia was found in both experimental groups. However, the way the observed model was introduced to participants did not affect the magnitude of placebo analgesia. Thus, the study showed that the role played by the model is not crucial for observationally induced placebo analgesia. The examined observer's individual characteristics did not predict the magnitude of placebo effect.

Nocebo hyperalgesia can be induced by classical conditioning without involvement of expectancy.

Influential theoretical accounts take the position that classical conditioning can induce placebo effects through conscious expectancies. In the current study two different conditioning procedures (hidden and open) were used to separate expectancy from conditioning in order to reveal the role of expectancy in the formation of nocebo hyperalgesia. Eighty-seven healthy females were randomly assigned to three groups (hidden conditioning, open conditioning, and control). Participants were selected according to the Fear of Pain Questionnaire scores and assigned to two subgroups: high and low level of fear of pain (trait). They received electrocutaneous pain stimuli preceded by either an orange or blue color. During the conditioning phase, one color was paired with pain stimuli of moderate intensity (control stimuli) and the other color was paired with pain stimuli of high intensity (nocebo stimuli) in both hidden and open conditioning groups. Only participants in the open conditioning group were informed about this association, however just before the testing phase the expectancy of hyperalgesia induced in this way was withdrawn. In the control group, both colors were followed by control pain stimuli. During the testing phase all participants received a series of stimuli of the same intensity, regardless of the preceding color. Participants rated pain intensity, expectancy of pain intensity and fear (state). We found that nocebo hyperalgesia was induced by hidden rather than open conditioning. The hidden conditioning procedure did not produce conscious expectancies related to pain. Nocebo hyperalgesia was induced in participants with low and high fear of pain and there was no difference in the magnitude of the nocebo effect between both groups. Nocebo hyperalgesia was not predicted by the fear of upcoming painful stimuli.

To Experience or to Be Informed? Classical Conditioning Induces Nocebo Hyperalgesia even when Placebo Analgesia Is Verbally Suggested-Results of a Preliminary Study.

OBJECTIVE: To investigate whether direct experience (i.e., classical conditioning) or verbal suggestion is more important in inducing nocebo hyperalgesia, five groups (total sample size, N = 99) were studied: conditioning, congruent conditioning, incongruent conditioning, verbal suggestion, and control. METHODS: Participants in groups with conditioning experienced more intensive pain stimuli after presentation of a white circle. In the congruent conditioning group, suggestion that the circle would precede more intensive pain stimuli was additionally provided, whereas in the incongruent conditioning group, the opposite suggestion was used. Control and verbal suggestion groups received pain stimuli of one intensity; however, the latter received suggestion that a circle would precede pain stimuli of higher intensity. RESULTS: The nocebo effect was observed in all conditioning groups, regardless of the verbal suggestions used. Moreover, the experience of hyperalgesia was able to nullify the effect of the verbal suggestion of analgesia. Incongruence between verbal suggestion and pain experience produced expectancies that affected nocebo hyperalgesia. CONCLUSIONS: The results of this preliminary study suggest that direct experience seems to be more important than verbal suggestion in inducing nocebo hyperalgesia.

Memory of pain in adults: a protocol for systematic review and meta-analysis.

BACKGROUND: The way pain is remembered and reported can affect medical decisions taken by patients and health-care professionals. Memory of pain has been investigated extensively for the past few decades; however, the results of previous studies are highly variable, indicating that the recollection of pain can be accurate, overestimated or underestimated. It is therefore difficult to conclude how well pain is remembered. The aim of this systematic review and meta-analysis is to summarize research findings on memory of pain in healthy adults and patients suffering from acute and chronic pain. METHODS: The systematic review will be performed by searching for articles indexed in the following databases: PubMed, MEDLINE, PsycINFO, Web of Science, ScienceDirect, PsycARTICLES, Scopus and Academic Search Complete. Studies will be included if (1) they investigated healthy adults or patients with any acute or chronic pain condition and if (2) they assessed experienced pain (pain intensity and/or pain unpleasantness) and its recollection. No restrictions related to the date of publication and recall delay will be applied. Studies will be screened for eligibility and risk of bias by two independent assessors. The risk of bias will be assessed by a modified Downs and Black checklist. A narrative synthesis will be performed in the first stage; in the second stage, the results of studies with comparable designs will be pooled in meta-analytical syntheses. DISCUSSION: The question of whether pain is remembered accurately is crucial for valid pain diagnosis, effective treatment and prognosis. So far, a number of studies on memory of pain have been conducted; however, a definitive conclusion on whether memory of pain is accurate is still lacking. In this systematic review and meta-analysis, available data will be pooled together to further inform research and clinical practice. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42018093523.

Color Hurts. The Effect of Color on Pain Perception.

Background Research suggests that colors may have an effect on human behavior, cognition, and emotions; however, little is known about their influence on pain perception. The aim of these two studies was to investigate whether colors have an impact on pain perception and to find the mechanism that underlies the influence of colors on pain. Methods In both studies, participants received electrocutaneous pain stimuli of the same intensity preceded by one of six colors (red, green, orange, blue, pink, or yellow) or a blank slide, which served as a control condition. In the first study, the intensity of experienced pain was measured; in the second study, both experienced and expected pain was measured. Results The studies revealed that colors increased the intensity of experienced pain in comparison with the noncolor condition (blank slide), regardless of both the sex of participants and whether they noticed a relationship between colors and pain intensity. Particularly, participants rated pain stimuli preceded by red as being more painful compared with pain stimuli preceded by other colors, especially green and blue. Conclusions It is concluded that colors have an impact on pain perception. Our results have important implications for the color lights paradigm applied in studies on placebo effects.

Rewarded placebo analgesia: A new mechanism of placebo effects based on operant conditioning.

BACKGROUND: Placebo analgesia is explained by two learning processes: classical conditioning and observational learning. A third learning process, operant conditioning, has not previously been investigated as a mechanism of placebo effects. We aimed to induce placebo analgesia by operant conditioning. METHODS: Three groups of participants received electrocutaneous pain stimuli of the same intensity, preceded by either an orange or blue stimulus. In the conditioning phase of the study, participants from the experimental group were rewarded for low pain responses following one of the colour stimuli (placebo) and for high pain responses following the other colour stimuli (non-placebo). Moreover, they were punished when their pain responses were high following placebo stimuli and low following non-placebo stimuli. To investigate the role of contingency, that is dependent relation between rewards/punishers and pain responses, the random-control group received rewards and punishers in a non-contingent manner. The colour-control group did not receive any rewards or punishers to control for nonassociative learning. Pain intensity ratings were used as an outcome measure, and verbal feedback on pain ratings was used as rewards/punishers. RESULTS: When rewarding and punishment were stopped, only participants from the experimental group experienced less pain following the placebo than following the non-placebo stimuli; that is, placebo analgesia was found in this group. This effect was not extinguished during the study. CONCLUSIONS: Placebo analgesia can be induced by operant conditioning, which should be considered a third mechanism for producing placebo effects. Moreover, the contingency between pain responses and rewards/punishers is crucial to induce placebo analgesia through operant conditioning. SIGNIFICANCE: According to the current placebo literature, placebo analgesia can be explained by two learning processes: classical conditioning and observational learning. A third learning process, operant conditioning, has not previously been investigated as a mechanism of placebo effects. Our study reveals that patients can learn placebo analgesia as a result of operant conditioning, suggesting that randomized controlled trials could be improved by controlling the reinforcement that might occur spontaneously when patients interact with, for example, medical personnel.