Attention And Perceptual Biases Related To Fear Of Pain

Chronic pain is pervasive and has devastating individual sufferers and costs for their families, and significant economic costs for society. Many chronic pain patients are unresponsive to medical interventions. However, psychological and behavioral factors can have a significant role in maintaining high levels of disability. The fear-avoidance model of chronic pain stated that pain-related fear is associated with escape or avoidance of activity and lead to physical disability. In the presence of physical injury or pain, people who are highly pain-fearful show hyper-vigilance towards internal and environmental pain stimuli and interpret pain sensations to be indications of ongoing tissue damage, even after healing has occurred. Fear of pain has an important role in the development and maintenance of chronic and disabling pain. Based on the fear-avoidance model of chronic pain, researchers assumed that the effects of fear of pain are maintained by processing biases towards internal and environmental pain signals. However, findings have been inconsistent regarding the presence of attention and perceptual biases related to fear of pain in clinical and experimental research. For example, in a recent functional Magnetic Resonance Imaging (fMRI) study, Barke et al.(2010) failed to identify brain activation differences in processing pain-related pictorial materials between chronic pain groups having higher and lower fear of movement levels.Purpose:The main purpose of this dissertation was1) to identify attention biases related to fear of pain using eye movement (EM) tracking technique, and2) to estimate perceptual biases related to fear of pain and use fMRI to explore its brain mechanisms. As such, the research provided more precise tests of the fear-avoidance model than most past studies. In this research, six studies were conducted in the service of examining attention and perceptual biases related to fear of pain.Methods:Studies1and2were conducted to assess the factor structure> reliability and validity of the Fear of Pain Questionnaire-Ⅲ (FPQ-III) in Chinese samples. In Study1,533undergraduates (402women,131men) completed the FPQ-III which was subjected to exploratory factor analysis (EFA). Study2assessed whether the EFA-derived solution or plausible alternative models of FPQ-III structure had the best fit using confirmatory factor analysis (CFA) in a separate sample of528undergraduates (395women,133men). In addition, Study2assessed the four-week stability and construct validity of the best fitting CFA solution in a subset (n=71) of the sample.Studies3and4used EM tracking to investigate selective attention biases differences related to fear of pain. In Study3, pain-free undergraduates (27women,14men) comprising higher (n=21) and lower (n=20) pain fearful groups based on FPQ-III scores responded to word pairs (i.e., sensory pain-neutral word, health-catastrophize-neutral word, neutral-neutral word) within a dot-probe paradigm. Eye-movements were tracked during stimulus presentations and RT was assessed following their offset. Study4extending the research by assessing attention biases related to fear of pain within both pain-free (20women,4men) and chronic pain samples matched on demographics (age, sex) and levels of emotional distress (depression, anxiety, stress). Specifically, the attention biases to pain-related information in chronic pain subgroups with high fear of pain (n=11) and low fear of pain (n=13) as well as pain-free subgroups with high fear of pain (n=11) and low fear of pain group (n=13) were assessed using the experimental paradigm and procedures described in relation to Study3.Study5-a, Study5-b, and Study6used threat manipulations adapted from Jackson et al.(2005) and Wiech et al.(2010) to assess effects of fear of pain and threat-value of stimuli on behavioral and perceptual responses. In Study5-a, pain-free undergraduates (35women,11men) were recruited into high (n=23) and low (n=23) fear of pain groups based on FPQ-III scores and engaged in a perception test to electric stimuli with near threshold pain on two skin sites on the left hand dorsum. To manipulate the threat level of electric stimulation, they were told (1) one skin site that which had been fully approved as safe because it was strong enough to tolerate electrical stimulation,(2) another skin site that had been approved with reservations because there was risk that electrical stimulation caused possible tissue or nerve damage. Subsequently,.participants completed the threatening pain task and their responses on pain judgments, pain ratings and anxiety level were assessed. Study5-b followed identical procedures in the same sample of study5-a, expect that the pain intensity of the electric stimulus were either at a higher or lower level. Their responses on pain ratings and anxiety level were assessed.Participants in Study6(14pain-free women,8pain-free men) engaged in an fMRI experiment following the same procedures as those used in Study5-a, except that the presentation time for the cues and "+" in each trial was longer. During the threatening pain task, the fMRI data were acquired and their responses on pain judgments, pain ratings and anxiety level were assessed.Results:Study1and Study2indicated that the25-item Chinese version of FPQ-Ⅲ included three factors such as medical pain, minor pain and severe pain, which was consistent with the original questionnaire’s structure. The three-factor model of Chinese version of FPQ-Ⅲ had relatively better structure validity than one-factor model, retest reliability.Study3found in healthy sample that high fear of pain participants directed more first fixation gaze towards sensory pain and health-catastrophize word, and had shorter first fixation latencies to sensory pain and health-catastrophize word than low FOP group. The first fixation gaze was defined as the first gaze fixated on one of the two words after onset of a word pair. The first fixation latency was defined as the time that individual takes to fixate the first gaze on one of the two words after the onset of a word pair. No FOP group differences were found for first fixation duration biases, overall gaze duration biases during stimulus presentations or RT to probes that followed stimulus offsets.Partially replicating the results of Study3, study4found that high FOP participants were more likely to direct first fixation gaze towards health-catastrophize word than those with low FOP. Furthermore, chronic pain patients had showed shorter first fixation duration to health-catastrophize word than pain free group. Null other FOP group or pain status differences were found for first fixation latency biases, overall gaze duration biases during stimulus presentations or RT to probes that followed stimulus offsets. Study4found that fear of pain and chronic pain reflected a vigilance-avoidance pattern of attentional biases in the early stages of processing health catastrophe words. Study5-a indicated that high FOP group were more likely to judge near threshold pain stimuli delivered to the higher threat skin site as "painful" compared to the low FOP group. The high fear of pain group also reported higher overall pain intensity and anxiety levels during the task than the low FOP group did. Study5-b found that high FOP group rated stimuli more painful and reported more anxiety when stimuli was delivered to the higher threat skin site, no matter that the pain intensity of the stimuli was either at a higher or lower level. Study5-a and Study5-b indicated that when pain was threatening, high FOP group always reported pain stimuli more painful and experienced more anxiety.The behavior results of Study6replicated Study5-a’s that high FOP group rated more threatening near threshold pain stimuli painful than low FOP group. Study6revealed significant main effects for FOP Group and Pain by a2FOP Group (high vs. low) x2Threat Level (high vs. low) x2Pain Decision (pain vs. no pain) analysis of the fMRI data in pain anticipation phase. Specifically, the high FOP group had stronger activation than the lower FOP group in regions related to arousal and emotional responses, such as the Cingulate Cortex, Insula, Thalamus, Parahippocampal Gyrus, middle orbital frontal Cortex. The main effect of Pain Decision indicated that participants had stronger activation for subjectively pain judgments than no pain judgments in regions related to pain judgment, such as insula, thalamus, superior frontal gyrus, middle/superior temporal gyrus, precuneus and supplementary motor area. However, no activation differences were found for Threat level nor were their signification interactions on fMRI data in pain anticipation phase. The significant main effect for FOP Group was revealed by a2FOP Group (high vs. low) x2Threat Level (high vs. low) x2Pain (pain vs. no pain) analysis of the fMRI data in post-stimulation phase. Specifically, the high FOP group had stronger activations than the low FOP group in regions related to emotion, such as middle orbital frontal cortex and middle frontal cortex. Notably, low FOP group had stronger activations in regions related to pain evaluation, such as insula, dorsolateral prefrontal cortex, and inferior frontal gyrus. However, no activation differences were found for Threat level, Pain nor were their signification interactions on fMRI data in pain anticipation phase.Conclusions:In sum, findings in this thesis supported that fear of pain was related to the processing biases to pain-related stimuli. First, healthy individuals with high FOP had the vigilance pattern of orienting attentional biases towards pain-related words. During the processing of pain-related words, the effects of fear of pain and chronic pain were shown as the vigilance-avoidance pattern of the orienting and maintenance attentional biases towards pain-related information. Second, the perceptual biases to threatening pain stimulus related to fear of pain were existed, whenever the pain intensity level was at a lower or higher level. The neural substrates of the perceptual biases to threatening pain might associate with the emotional brain areas during pain anticipation period, such as cingulate cortex, insula, thalamus, parahippocampal gyrus, middle orbital frontal cortex. Findings in this thesis identified the attention and perceptual biases related to fear of pain, and provided empirical evidences for the fear-avoidance model of chronic pain and transactional model of stress.