The effects of underestimated pain and their relationship to habituation

The intensity of a painful stimulus was experimentally manipulated in order to induce underpredictions of pain. The experiment aimed at (1) replicating previous findings on the effects of underpredicted pain and (2) investigating the relationship between underpredicted pain and habituation. Most previous findings were replicated: underpredictions of pain were followed by raised expectations of pain and increased fear of pain. In addition, the underprediction had long-term effects on fear of pain, uncertainty about predictions, and expected aversiveness of the painful stimulus. In contrast to previous findings and to Rachman's match/mismatch model, it was found that underpredicted pain can have dishabituating effects. It is theorized that inaccurately predicted pain can cause dishabituation, depending on the extent of the underprediction and on the subjective certainty of the prediction. Theoretical and clinical implications are discussed.     

Why do people tend to overpredict pain? On the asymmetries between underpredictions and overpredictions of pain

After an underpredicted painful experience people tend to expect increased pain levels for a considerable time, despite disconfirmatory experiences. Underpredictions also tend to raise long-lasting fear and increased physiological responding. Overpredicted pain does not have such dramatic effects. What are the reasons for this asymmetry? Evidence for and against the hypothesis that underpredicted pain hurts more than correctly predicted pain, and that overpredictions result from a tendency to avoid the extra aversiveness of underpredictions, is reviewed. Based on recent experiments this explanation is rejected, and alternative explanations are discussed. It is reasoned that the most plausible explanation is that the organism automatically infers danger from an underprediction, because of the loss of predictability into the dangerous direction (i.e. more pain). Elevated expectancy and fear levels are the result of this. A modified stimulus-comparator model that accounts for the differential effects of both types of incorrect predictions is suggested. In contrast to previous models, such a model hypothesizes: (i) differential processing of under- and overpredictions; and (ii) different processes involved in the influence of expectations on subjective and non-subjective pain responses.     

Underpredicted pain disrupts more than correctly predicted pain, but does not hurt more

One of the explanations for the negative effects of underpredicted aversive experiences is that they have more impact than correctly predicted aversive experiences. In a laboratory experiment 40 normal female subjects executed an auditory discrimination task. Subjects were randomly assigned to a correct information condition and an underprediction information condition. After ten trials (baseline) subjects were informed that they would receive some painful (correct prediction) or non-painful tingling (underprediction) stimuli during the discrimination task. Starting just before five of the following 20 discrimination trials, 2 s of painful electrical stimulation was given. Subjects rated sensations and painfulness of the electrical stimulation, subjective anxiety, and degree of distraction from the task, after each pain stimulus. Reaction times of the discrimination task and heart rate were measured. Underprediction information resulted in lower pain ratings, but stronger heart rate responses and higher disruption on the discrimination task, compared to correct information. This suggests that while underpredictions of pain do not hurt more, disruption on primary tasks and physiological impact are higher. Underpredicted pain has more impact than correctly predicted pain, not because it hurts more, but because it conveys inherent danger information.     

Attention, not anxiety, influences pain

Four hypotheses about the influences of anxiety and attention on pain impact were tested in a critical experiment: (1) anxiety increases pain; (2) anxiety decreases pain; (3) attention to pain increases pain; (4) only the combination of anxiety and attention to pain increases pain (interaction hypothesis). In a 2 x 2 design, anxiety (low vs high) and attention (attention vs distraction from the pain) were experimentally manipulated. Subjects received 20 electrically produced painful stimuli. Subjective pain experiences, skin conductance responses and heart rate responses gave no support for a pain impact increasing effect of anxiety. The anxiety-attention interaction hypothesis did not receive any support either. There was some support, only from the heart rate responses, that anxiety reduces pain impact. The critical factor appeared to be attention. Attention to the pain stimulus was related to a stronger pain impact (indicated by all measures) and to less subjective habituation, compared to distraction.     

Degree of extraversion and physiological responses to physical pain and sadness

Extraversion is a personality frequently discussed as one of the strongest and most consistent factors that relates to individual subjective wellbeing. The goal of this study was to better understand how people with varying degrees of extraversion psychologically and physiologically respond differently to unpleasant circumstances. Emotional responses (e.g., levels of intensity, valence, and arousal) were assessed in determining the sensitivity level to negative stimuli that were specifically designed to provoke physical pain and sadness emotion. Physiological changes (e.g., heart rate (HR), blood volume pulse (BVP), and respiratory sinus arrhythmia (RSA)) were also measured during pain and sadness to observe sympathetic and parasympathetic activities. Our results showed that the degree of extraversion was associated with less unpleasant responses to sadness, less HR responses to both pain and sadness, and greater RSA responses to sadness. The findings suggest that the lower HR reactivity to painful and sad situations and greater RSA reactivity to sad situations in extraversion could be possibly due to increased parasympathetic activity. Additionally, enhanced parasympathetic activity to negative situations may explain an important mechanism underlying the positive connection between extraversion and subjective wellbeing.     

Avoidance of pain of unpredictable intensity

Unpredictability of the intensity of an aversive event might be an important factor in producing negative effects of the event, especially if the UCS becomes stronger than could have been expected. The present experiment tested the hypothesis that unpredictability of intensity of a painful stimulus contributes to avoidance behaviour. The experiment was concealed in a shock working-up procedure, which was done to assess the pain level subjects were willing to tolerate in a subsequent experiment. The experimental subjects, who received an unannounced sudden increase of the pain stimulus during the working-up procedure, tolerated less pain on a subjective as well as on an objective level (avoidance of high levels of pain) than the control subjects, who received the stimuli in a predictable pattern. The results support the hypothesis that unpredictability of intensity of an aversive event contributes to avoidance behaviour.     

The role of anxiety sensitivity in subjective and physiological responses to social and physical stressors

This study examined the specificity of the relationship between anxiety sensitivity (AS), a measure of catastrophizing about arousal-related sensations, and pain responses, by examining the effect of AS on responses to stressors of a physical and social nature. Healthy men and women (n = 129) between the ages of 18 and 25 years were recruited from the community to participate in a study examining subjective, cognitive and behavioural responses to different types of stressors. Participants were randomly assigned to one of 3 groups: (i) a neutral condition in which they sat quietly and read a popular magazine; (ii) a social stress condition in which they anticipated having to give a self-disclosing speech; and (iii) a physical stress condition in which they were presented with 3 countdown to shock trials where a mild electrical shock was administered on the non-dominant arm. Subjective ratings and physiological responses were recorded in anticipation of the stressor and immediately after stress exposure. Results indicated that AS was indirectly related to pain ratings via its effect on anticipatory anxiety ratings. AS was associated with anticipatory anxiety ratings, regardless of whether the stressor was of a physical or social nature. Furthermore, AS was not shown to be directly associated with exaggerated subjective or physiological reactions to the physical stressor. These results indicate that the role of AS in pain responses may be mediated through a global effect on anxiety, and limited to the anticipatory stage of the pain experience. If future studies yield similar findings in pain patients, then they would suggest that interventions for helping individuals high in AS should focus on catastrophic thinking in anticipation of stressors in general, rather than on pain-specific stressors.     

Relationships among anxious symptomatology, anxiety sensitivity and laboratory pain responsivity in children

Existing laboratory-based research in adult samples has suggested that anxiety sensitivity (AS) increases an individual's propensity to experience pain-related anxiety, which in turn enhances pain responsivity. Such relationships have not been examined in younger populations. Thus, the present study used structural equation modeling (SEM) to test a conceptual model in which AS would evidence an indirect relationship with pain intensity via its contribution to state-specific anticipatory anxiety in relation to a variety of laboratory pain tasks (cold pressor, thermal heat, and pressure pain) in 234 healthy children (116 girls; mean age = 12.6 years, range = 8-18 years). The model further hypothesized that existing anxious symptomatology would demonstrate a direct relationship with pain intensity. Results of the SEM supported the proposed conceptual model with the total indirect effect of AS accounting for 29% of the variance in laboratory pain intensity via its effects on pain-related anticipatory anxiety. AS did not however, evidence a direct relationship with pain intensity. Anxious symptomatology on the other hand, demonstrated a significant direct effect on pain intensity, accounting for 15% of variance. The combined effects of AS, anxiety symptoms, and anticipatory anxiety together explained 62% of the variance in pain intensity. These relationships did not differ for boys and girls, indicating no moderating effect of sex in the proposed model. The present results support the potential benefit of assessing both AS and anxiety symptoms in children prior to undergoing painful stimulation.     

Predictions of dental pain: the fear of any expected evil, is worse than the evil itself

In a study of 40 subjects, who twice underwent extensive dental treatment, the relationships between expectations and experiences of pain and of anxiety were investigated. Inaccurate expectations were adjusted in the same way as observed in the laboratory. Especially anxious subjects expected more pain and anxiety than they experienced, and they appeared to need more experiences before their predictions became accurate. In the course of time, the expectations (and memories) of anxious subjects returned to their original more inaccurate level of prediction. The results suggest that the old schema is ultimately reinstated if disconfirmations are few and far between. Anxious subjects did not experience more pain, but they did experience more anxiety than fearless subjects. Detailed investigation of processes of change after disconfirmation showed that anxiety experienced during treatment is a factor that plays a part in maintaining the problem of inaccurate expectations and fear of treatment. Theoretical and clinical implications of these findings are discussed.     

An exploratory analysis of the influence of personality and emotional factors on cerebral blood flow responses during painful stimulation in Fibromyalgia

This study explored the influence of certain personality traits (neuroticism, extraversion, psychoticism, alexithymia), emotional variables (depression, catastrophizing), and insomnia on cerebral blood flow (CBF ) responses to painful stimulation in fibromyalgia, using functional transcranial Doppler sonography. CBF velocities were recorded bilaterally in the anterior cerebral arteries (ACA ) and middle cerebral arteries (MCA ) of 24 fibromyalgia patients during exposure to two painful pressure conditions: (1) fixed pressure (2.4 kg) and (2) an individually calibrated pressure to produce an equal‐moderate subjective pain intensity in all participants (average, 3.5 kg). Psychological factors were assessed by means of questionnaires. Neuroticism, and the externally‐oriented thinking dimension of alexithymia were positively, and extraversion was inversely, associated with specific components of ACA and MCA CBF responses. Regarding catastrophizing and depression, correlations were positive for the fixed pressure condition and negative for the equal subjective intensity condition. The findings suggest that alterations in central nervous pain processing in fibromyalgia vary according to psychological factors. While most of the observed associations reflect a linear increase in nociceptive processing with the magnitude of negative cognitive and emotional states, the inverse associations for catastrophizing and depression during more intense painful stimulation may be ascribed to anti‐nociceptive effects due to activation of the defense reflex.     

The relationship between underpredicted pain and escape

Escape and avoidance that are disproportional to the danger of the pertinent stimulus are important clinical problems that are often related to inaccurate (catastrophic) expectations. One possible source of such expectations is a prior, underestimated aversive experience. In the present experiment the hypotheses that underestimated pain leads to escape and that it leads to avoidance were tested. In order to control for the effect of the intensity of the pain stimulus, a control group that received 20 pain stimuli of high intensity was formed. Subjects in the experimental condition received 17 pain stimuli of low intensity and 3 of (unexpectedly) high intensity (experimentally induced underprediction). Underprediction of the high intensity stimulus was significantly related to escape, but not to avoidance. The results suggest that the way in which avoidance was operationalized accounts for this. The strong support of the hypothesized relationship between underpredicted pain and escape is an important finding, however.     

The effect of UCS inflation and deflation procedures on 'fear' conditioning

Davey (1992: Classical conditioning and the acquisition of human fears and phobias: a review and synthesis of the literature. Advances in Behaviour Research and Therapy, 14, 29-66) hypothesized that subjective revaluation of an unconditioned stimulus (UCS) would determine the strength of the autonomic conditioned response (CR) in the fear conditioning paradigm. The purpose of the present study was to examine the effect of UCS aversiveness on the CR strength in the fear conditioning paradigm. The UCS aversiveness was controlled by the UCS intensity; that is, the UCS intensity was increased for the inflation group or decreased for the deflation group. Thirty subjects were randomly assigned to the inflation or the deflation group, and they participated under both experimental and control conditions. All subjects went through the pretest, the acquisition of classical conditioning, the UCS intensity operation, and the test sessions. The indices of the CR were skin conductance responses (SCRs) and a subjective aversion to the conditioned stimulus (CS). The main results were as follows. (1) The CR strength measured by SCR was increased by the UCS inflation and decreased by the UCS deflation. (2) The subjective aversiveness of the CS was not sensitive to both manipulations of UCS intensity. These results suggested that the autonomic CR strength might be influenced by the subjective revaluation of UCS, as Davey (1992) described. The result from the test of the subjective aversiveness of the CS, however, could not support Davey's model. The difference between expressions of the SCR and the subjective aversiveness of the CS might be caused by different learning systems.     

Optimal response biases and the slope of ROC curves as a function of signal intensity,signal probability,and relative payoff

Rats performed in a two-lever analogue of the yes-no psychophysical procedure. The signal consisted of of an increment in the intensity of a random noise. Correct responses were reinforced with single bursts of brain stimulation; incorrect responses produced brief periods of time-out. Receiver-operating-characteristic curves were generated at each of several signal intensities by varying either the signal probability (0.1–0.9) or the relative number of brain stimulations for correct responses (1:3–3:1). The index d’ (or d’_e) increased with the signal intensity and was independent of response bias. When the signal probability was varied, the animals optimized the number of correct trials. and hence the number of brain stimulations obtained at each level of detection. They approximated this optimum more closely as the signal intensity was reduced. When the ratio of brain stimulations was varied, the animals compromised between optimizing the number of correct trials and optimizing the number of brain stimulations obtained. The slopes of the ROC curves plotted on normal-normal coordinates frequently departed from unity, but did not change systematically with either the signal intensity or the method by which they were generated.     

Alcohol and unpleasant stimulation: subjective shock calibration and pain and discomfort perception

In an experiment 8 men participated in an alcohol and a sober condition in a rotated order. In both conditions subjects first calibrated a shock scale to a subjective criterion and then rated their subjective pain and total discomfort. Subjects calibrated the shock scale higher when intoxicated and rated the calibrated level equally painful in the sober and intoxicated conditions, but when intoxicated subjects actually rated the higher shock level as less uncomfortable. The shock scale was calibrated higher under intoxication not because subjects wanted to impress the experimenter but because less pain and discomfort was actually experienced.     

Predicting Individuals’ Experienced Fear From Multimodal Physiological Responses to a Fear-Inducing Stimulus

Emotions are experienced differently by individuals, and thus, it is important to account for individuals’ experienced emotions to understand their physiological responses to emotional stimuli. The present study investigated the physiological responses to a fear-inducing stimulus and examined whether these responses can predict experienced fear. A total of 230 participants were presented with neutral and fear-inducing film clips, after which they self-rated their experienced emotions. Physiological measures (skin conductance level and response: SCL, SCR, heart rate: HR, pulse transit time: PTT, fingertip temperature: FT, and respiratory rate: RR) were recorded during the stimuli presentation. We examined the correlations between the physiological measures and the participants’ experienced emotional intensity, and performed a multiple linear regression to predict fear intensity based on the physiological responses. Of the participants, 92.5% experienced the fear emotion, and the average intensity was 5.95 on a 7-point Likert scale. Compared to the neutral condition, the SCL, SCR, HR, and RR increased significantly during the fear-inducing stimulus presentation whereas FT and PTT decreased significantly. Fear intensity correlated positively with SCR and HR and negatively with SCL, FT, PTT, and RR. The multiple linear regression demonstrated that fear intensity was predicted by a combination of SCL, SCR, HR, FT, and RR. Our findings indicate that the physiological responses to experiencing fear are associated with cholinergic, sympathetic, and α-adrenergic vascular activation as well as myocardial β-sympathetic excitation, and support the use of multimodal physiological signals for quantifying emotions.     

The effect of exercise and childbirth classes on fear of childbirth and locus of labor pain control

This study sought to track changes in intensity of fear of childbirth and locus of labor pain control in women attending an exercise program for pregnant women or traditional childbirth classes and to identify the predictors of these changes. The study was longitudinal/non-experimental in nature and run on 109 healthy primigravidae aged from 22 to 37, including 62 women participating in an exercise program for pregnant women and 47 women attending traditional childbirth classes. The following assessment tools were used: two scales developed by the present authors – the Fear of Childbirth Scale and the Control of Birth Pain Scale, three standardized psychological inventories for the big five personality traits (NEO Five Factors Inventory), trait anxiety (State–Trait Anxiety Inventory) and dispositional optimism (Life Oriented Test–Revised) and a questionnaire concerning socioeconomic status, health status, activities during pregnancy, relations with partners and expectations about childbirth. Fear of childbirth significantly decreased in women participating in the exercise program for pregnant women but not in women attending traditional childbirth classes. Several significant predictors of post-intervention fear of childbirth emerged: dispositional optimism and self-rated health (negative) and strength of the belief that childbirth pain depends on chance (positive).     

The effect of situation-evoked anxiety and gender on pain report using the cold pressor test

The aims of the present study were to investigate the influence of anxiety on pain perception and to test whether gender differences in pain perception are anxiety dependent. Sixty male and female university students exposed to situation-evoked anxiety or a control procedure were measured for their pain threshold, tolerance, and perceived intensity during a cold pressor test. Both subjective and autonomic responses indicated that anxiety was successfully induced in participants exposed to the anxiety condition. Increased situational anxiety had no significant effect on pain threshold or pain tolerance. Significant increases in pain intensity were found for the anxiety group. Levels of anxiety, however, did not correlate with this increased intensity, raising doubt as to the role of anxiety in producing this effect. No gender differences were found for pain tolerance or pain intensity. Gender differences were found for pain threshold in the anxiety group with, contrary to past findings, females showing significantly higher pain thresholds than males. The results are discussed in the light of related studies.     

Impact of anticipatory processing versus distraction on multiple indices of anxiety in socially anxious individuals

In models of social phobia, anticipatory processing before a social-evaluative event is a key maintaining factor for the disorder. This study investigated the impact of anticipatory processing versus distraction before a social-evaluative task on affective (self-reported anxiety), psychophysiological (skin conductance), cognitive (self-reported maladaptive self-beliefs) and behavioural (in-situation performance) responses of participants. High and low socially anxious undergraduates were randomly allocated to either an anticipatory processing or distraction condition, and then completed an impromptu speech task. Relative to distraction, anticipatory processing increased self-reported anxiety in all participants, and increased skin conductance and the strength of conditional and high standard beliefs in the high (but not low) socially anxious participants. Unconditional beliefs were not affected. For high socially anxious individuals, anticipatory processing was also indirectly associated with poorer speech performance by increasing self-reported anxiety. Anticipatory processing appears to have multiple adverse effects in socially anxious individuals.     

A cognitive neuropsychological and psychophysiological investigation of a patient who exhibited an acute exacerbated behavioural response during innocuous somatosensory stimulation and movement

We report findings from a cognitive neuropsychological and psychophysiological investigation of a patient who displayed an exacerbated acute emotional expression during movement, innocuous, and aversive somatosensory stimulation. The condition developed in the context of non-specific white matter ischaemia along with abnormalities in the cortical white matter of the left anterior parietal lobe, and subcortical white matter of the left Sylvian cortex. Cognitive neuropsychological assessment revealed a pronounced deficiency in executive function, relative to IQ, memory, attention, language and visual processing. Compared to a normal control group, the patient [EQ] displayed a significantly elevated skin conductance level during both innocuous and aversive somatosensory stimulation. His pain tolerance was also significantly reduced. Despite this, EQ remained able to accurately describe the form of stimulation taking place, and to rate the levels of pain intensity and pain affect. These results suggest that EQ's exaggerated behavioural response and reduced pain tolerance to somatosensory stimulation may be linked to cognitive changes, possibly related to increased apprehension and fear, rather than altered pain intensity or pain affect per se.