The detectability, discriminability, and perceived magnitude of painful electrical shock

The association of the localized pain sensitivity in the residual limb and prosthesis use in male veterans with transtibial amputation

The association of localized pain sensitivity in the residual limb and prosthesis use has clinical implications, however, rarely been assessed. This study aimed to investigate pain sensitivity and explore its range, variability, and association with prosthesis use alongside other demographic and clinical characteristics of veterans with transtibial amputation. Pain sensitivity was determined as pressure pain threshold (PPT) and pressure tolerance (PT) in 19 male veterans with a mean age of 49.5 years using pressure algometry at 12 anatomical locations on‎ the residual limb. A comparison of pain sensitivity at each location, and among anatomical locations and participants was explored using independent t-test, analysis of variance, and Kruskal-Wallis tests, respectively. Pain sensitivity range (PSR), the difference between PT and PPT, was significantly different (p < 0.05) at mid-patellar tendon, medial tibial flare, and the distal end of the tibia. The lowest PPT and PT (20.5 and 33 Ncm-2, p = 0.13) were recorded at the distal end of the residual limb, and the highest PPT and PT (73.4 and 94.3 Ncm-2, p = 0.03) were recorded at the mid-patellar tendon. Pain sensitivity was significantly different among anatomical locations and participants. The correlation tests (Pearson and partial eta squared) showed non-significant associations of pain sensitivity with participants' demographic and clinical characteristics except for daily prosthesis use. The mid-patellar tendon, medial tibial flare, and distal end of the tibia revealed the lowest pain hypersensitivity ‎due to higher PSR. Longer daily prosthesis use was associated with increased pain sensitivity.

Selective and replicable neuroimaging-based indicators of pain discriminability

Neural indicators of pain discriminability have far-reaching theoretical and clinical implications but have been largely overlooked previously. Here, to directly identify the neural basis of pain discriminability, we apply signal detection theory to three EEG (Datasets 1-3, total N = 366) and two fMRI (Datasets 4-5, total N = 399) datasets where participants receive transient stimuli of four sensory modalities (pain, touch, audition, and vision) and two intensities (high and low) and report perceptual ratings. Datasets 1 and 4 are used for exploration and others for validation. We find that most pain-evoked EEG and fMRI brain responses robustly encode pain discriminability, which is well replicated in validation datasets. The neural indicators are also pain selective since they cannot track tactile, auditory, or visual discriminability, even though perceptual ratings and sensory discriminability are well matched between modalities. Overall, we provide compelling evidence that pain-evoked brain responses can serve as replicable and selective neural indicators of pain discriminability.

Neural and Self-report Measures of Sensitivity to Uncertainty as Predictors of COVID-Related Negative Affect

The COVID-19 pandemic has been a period of unprecedented uncertainty. Research indicates individuals differ in their response to uncertainty and these differences are mediated by anterior insula (aINS) function. Those most sensitive to uncertainty are likely vulnerable to negative affect in the context of the pandemic. The current study was designed to directly test this question using both neural and self-reported measures of sensitivity to uncertainty. Fifty-nine volunteers completed a task designed to probe neural response to anticipation of predictable (P-) and unpredictable (U-) threat-of-electric-shock during functional magnetic resonance imaging and a self-report measure of intolerance of uncertainty (IU). Approximately two years later, during the peak of the pandemic, participants reported their emotional reactions to the COVID-19 crisis. Multilevel mixed models revealed that greater aINS activation to U-threat and greater self-reported IU were independent predictors of increased COVID-related negative affect. These findings were significant when adjusting for biological sex and depression and anxiety symptom severity. The results add to a growing literature demonstrating that individual differences in response to uncertainty have a robust impact on mood and functioning. Results also highlight that individuals highly sensitive to uncertainty may be at increased risk for poor mental health during the ongoing pandemic.

Shared and unique neural circuitry underlying temporally unpredictable threat and reward processing

Temporally unpredictable stimuli influence behavior across species, as previously demonstrated for sequences of simple threats and rewards with fixed or variable onset. Neuroimaging studies have identified a specific frontolimbic circuit that may become engaged during the anticipation of temporally unpredictable threat (U-threat). However, the neural mechanisms underlying processing of temporally unpredictable reward (U-reward) are incompletely understood. It is also unclear whether these processes are mediated by overlapping or distinct neural systems. These knowledge gaps are noteworthy given that disruptions within these neural systems may lead to maladaptive response to uncertainty. Here, using functional magnetic resonance imaging data from a sample of 159 young adults, we showed that anticipation of both U-threat and U-reward elicited activation in the right anterior insula, right ventral anterior nucleus of the thalamus and right inferior frontal gyrus. U-threat also activated the right posterior insula and dorsal anterior cingulate cortex, relative to U-reward. In contrast, U-reward elicited activation in the right fusiform and left middle occipital gyrus, relative to U-threat. Although there is some overlap in the neural circuitry underlying anticipation of U-threat and U-reward, these processes appear to be largely mediated by distinct circuits. Future studies are needed to corroborate and extend these preliminary findings.

Nonlinear increase of pain in distance-based and area-based spatial summation

ABSTRACT

When nociceptive stimulation affects a larger body area, pain increases. This effect is called spatial summation of pain (SSp). The aim of this study was to describe SSp as a function of the size or distance of a stimulated area(s) and to test how this function is shaped by the intensity and SSp test paradigm. Thirty-one healthy volunteers participated in a within-subject experiment. Participants were exposed to area-based and distanced-based SSp. For area-based SSp, electrocutaneous noxious stimuli were applied by up to 5 electrodes (5 areas) forming a line-like pattern; for distance-based SSp, the same position and lengths of stimuli were used but only 2 electrodes were stimulated. Each paradigm was repeated using pain of low, moderate, and high intensity. It was found that the pattern of pain intensity followed a logarithmic (power) rather than a linear function. The dynamics of the pain increase were significantly different across pain intensities, with more summation occurring when pain was perceived as low. Results indicated that area-based SSp is more painful than distance-based SSp when low and moderate but not when high pain intensity is induced. Presented findings have important implications for all studies in which the spatial dimension of pain is measured. When the area or separation between nociceptive stimulation increases, pain does not increase linearly and the pattern of the pain increase is a result of the interaction between intensity and the number of nociceptive sites. A power function should be considered when predicting the size of a nociceptive source.

Detectability and Bias Indices of Pneumatic Corneal Stimuli Using Signal Detection Theory

Purpose

To evaluate the feasibility of using signal detection theory (SDT) in estimating criterion and detectability indices for corneal pneumatic stimuli and test corneal psychophysical data against linking hypotheses from nonprimate physiology using Bayesian analysis.

Methods

Corneal pneumatic stimuli were delivered using the Waterloo Belmonte esthesiometer. Corneal thresholds were estimated in 30 asymptomatic participants and 1.5× threshold stimuli were used as signals (with 0.4 probability). There were 100-trial mechanical and cold stimulus experiments and 50-trial chemical experiments. Trials were demarcated auditorily and "yes" or "no" recorded after each trial. Cold stimulus experiments were conducted with 0.6 signal probability. Criterion (c), likelihood ratio (lnβ), and d' were calculated from the yes-no responses.

Results

Average d' was 0.59 ± 0.1, 1.65 ± 0.37, and 1.14 ± 0.3 units for cold, mechanical, and chemical stimuli, respectively. Bayes factors obtained using Bayesian analysis of variance mildly favored (BF10 = 1.55) differences between d's of the stimulus types, with no support for differences in criteria between stimulus types. Multiple comparisons of d' supported linking hypotheses based on nociception and nerve conductance theories.

Conclusions

Our experiments are the first to demonstrate the feasibility of estimating SDT indices and test different hypotheses. The conservative strategy (reporting "no" more often) chosen by participants was anticipated due to relatively large proportion of catch trials.

Translational Relevance

SDT when using pneumatic esthesiometry is vital to evaluate bias in responses of participants. Considering the varied forms of inherent noise in the corneal sensory system, SDT is critical to understand the sensory and decisional characteristics.

The Relation Between Posttraumatic Stress Symptom Severity and Startle Potentiation to Predictable and Unpredictable Threat

Aberrant threat reactivity has been implicated in the pathophysiology of posttraumatic stress disorder (PTSD); however, the literature on this association is mixed. One factor that may contribute to this inconsistent association is differences in severity of posttraumatic stress symptoms (PTSSs) across studies, but no studies have tested this hypothesis. The relation between PTSD and threat reactivity may also differ between unpredictable threats (U-threats) and predictable threats (P-threats), given burgeoning evidence to support a particular role for aberrant responding to U-threat in PTSD. The present study examined how PTSS severity relates to startle potentiation to U-threat and P-threat in a trauma-exposed community sample (N = 258). There was a negative linear, but not quadratic, relation between PTSS severity and startle potentiation to U-threat, but not P-threat. Blunted defensive responding to U-threat may therefore contribute to higher levels of PTSSs and may represent a novel treatment target for higher levels of PTSSs.

The impact of startle reactivity to unpredictable threat on the relation between bullying victimization and internalizing psychopathology

BACKGROUND

Being bullied has detrimental effects on mental health functioning. Individuals who are highly reactive to unpredictable threats (U-threat) may be particularly vulnerable to the negative consequences of being bullied. For them, persistent, unpredictable bullying likely elicits chronic anticipatory anxiety and depression. The aim of the present study was to examine the main and interactive effects of aversive reactivity to U-threat and past-year bullying victimization on current anxiety and depressive symptoms.

METHODS

Seventy-one young adults (ages 17-19) completed a well-validated threat-of-shock task used to probe reactivity to both U-threat and predictable threat (P-threat). Startle eyeblink potentiation was recorded to index aversive responding.

RESULTS

We found a main effect of bullying, such that individuals with more bullying experience exhibited greater anxiety and depressive symptoms than individuals with less bullying experience. There was also a bullying by U-threat reactivity interaction such that among individuals with high reactivity to U-threat, more bullying experience was associated with more anxiety and depressive symptoms. Among individuals with low U-threat reactivity, there was no association between bullying and internalizing symptoms. There were no main or interactive effects involving reactivity to P-threat.

CONCLUSIONS

Together, these results suggest that among individuals who are bullied, those who are sensitive to U-threat are particularly vulnerable to depression and anxiety in young adulthood. These individuals may represent a high-risk group for the development of internalizing psychopathology.

Reproducibility of a battery of human evoked pain models to detect pharmacological effects of analgesic drugs

BACKGROUND

Although reproducibility is considered essential for any method used in scientific research, it is investigated only rarely; thus, strikingly little has been published regarding the reproducibility of evoked pain models involving human subjects. Here, we studied the reproducibility of a battery of evoked pain models for demonstrating the analgesic effects of two analgesic compounds.

METHODS

A total of 81 healthy subjects participated in four studies involving a battery of evoked pain tests in which mechanical, thermal and electrical stimuli were used to measure pain detection and tolerance thresholds. Pharmacodynamic outcome variables were analysed using a mixed model analysis of variance, and a coefficient of variation was calculated by dividing the standard deviation by the least squares means.

RESULTS

A total of 76 subjects completed the studies. After being administered pregabalin, the subjects' pain tolerance thresholds in the cold pressor and pressure stimulation tests were significantly increased compared to the placebo group. Moreover, the heat pain detection threshold in UVB-irradiated skin was significantly increased in subjects who were administered ibuprofen compared to the placebo group. Variation among all evoked pain tests ranged from 2.2% to 30.6%.

CONCLUSIONS

Four studies using a similar design showed reproducibility with respect to the included evoked pain models. The relatively high consistency and reproducibility of two analgesics at doses known to be effective in treating clinically relevant pain supports the validity of using this pain test battery to investigate the analgesic activity and determine the active dosage of putative analgesic compounds in early clinical development.

SIGNIFICANCE

The consistency and reproducibility of measuring the profile of an analgesic at clinically relevant doses illustrates that this pain test battery is a valid tool for demonstrating the analgesic activity of a test compound and for determining the optimal active dose in early clinical drug development.

Neural correlates of predictable and unpredictable threat in internalizing psychopathology

Converging lines of evidence suggest that heightened responding to unpredictable threat may be an important neurobiological marker of internalizing psychopathology (IP). Prior data also indicate that aversive responding to uncertainty may be mediated by hyperactivation of several brain regions within the frontolimbic circuit, namely the anterior insula (aINS) and the dorsal anterior cingulate cortex (dACC). To date, however, the majority of this research has been focused on individual diagnoses and it is unclear whether abnormal neural reactivity to unpredictable threat is observed within heterogeneous, transdiagnostic IP patient populations, as theory would suggest. The aim of the current study was to therefore examine the neural correlates of temporally unpredictable (U) and predictable (P) threat in a sample of healthy controls (n = 24) and patients with a broad range of IP diagnoses (n = 51). We also examined whether symptom severity measures of fear and distress/misery dimensions correlated with neural reactivity to U- and P-threat. All participants completed a modified version of a well-validated threat-of-shock task during functional magnetic resonance imaging (fMRI). Across all participants, U- and P-threat elicited heightened activation in the aINS and brainstem, while P-threat alone also activated the dACC. Relative to healthy controls, patients displayed greater activation in the right aINS during U-threat, and greater right brainstem activation during P-threat. In addition, we found that brainstem activity during U-threat correlated with fear, but not distress/misery, psychopathology. Taken together, these preliminary results suggest that exaggerated aINS reactivity during U-threat and brainstem reactivity during P-threat may have the potential to become important transdiagnostic biomarkers of IP; however, future research efforts are needed to corroborate and expand the present findings.

The time course of responding to aversiveness in females with a history of non-suicidal self-injury

Non-suicidal self-injury is a risk factor for suicidal behavior, particularly in females. Two prominent theories of suicide suggest that habituation to the psychophysiological aversiveness of NSSI is a mechanism by which NSSI exposure may lead to increased risk for suicide. Several laboratory studies examining the relationship between physiological habituation and suicide attempt history have yielded mixed results, potentially due to their use of broad measures of physiological arousal and/or focus on specific psychopathologies. However, no studies have examined the association between the time course (e.g., habituation, initial reactivity) of responding to aversiveness and NSSI, which may help to elucidate psychophysiological mechanisms of NSSI. Therefore, we examined habituation and initial reactivity to aversiveness (indexed by the time course of acoustic startle reflex, a well-validated measure of defensive responding) in three groups of young adult females - those with a history of NSSI, psychiatric controls matched on potential confounds (e.g., psychopathology, trauma history, demographics), and healthy controls. Results indicated that individuals with a history of NSSI exhibited blunted initial reactivity and marginally slower habituation to aversiveness relative to the two control groups. The NSSI group's insensitivity to aversiveness may reflect prior psychophysiological habituation, and may be a mechanism through which prior NSSI exposure leads to increased risk for suicidal behavior.

Vigilance-related attention systems subserve the discrimination of relative intensity differences between painful stimuli

Humans require the ability to discriminate intensities of noxious stimuli to avoid future harm. This discrimination process seems to be biased by an individual's attention to pain and involves modulation of the relative intensity differences between stimuli (ie, Weber fraction). Here, we ask whether attention networks in the brain modulate the discrimination process and investigate the neural correlates reflecting the Weber fraction for pain intensity. In a delayed discrimination task, participants differentiated the intensity of 2 sequentially applied stimuli after a delay interval. Compared with nonpain discrimination, pain discrimination performance was modulated by participants' vigilance to pain, which was reflected by the functional connectivity between the left inferior parietal lobule and the right thalamus. Of note, this vigilance-related functional coupling specifically predicted participants' behavioral ability to differentiate pain intensities. Moreover, unique to pain discrimination tasks, the response in the right superior frontal gyrus linearly represented the Weber fraction for pain intensity, which significantly biased participants' pain discriminability. These findings suggest that pain intensity discrimination in humans relies on vigilance-related enhancement in the parieto-thalamic attention network, thereby allowing the prefrontal cortex to estimate the relative intensity differences between noxious stimuli.

Factors Affecting and Adjustments for Sex Differences in Current Perception Threshold With Transcutaneous Electrical Stimulation in Healthy Subjects

OBJECTIVE

Current perception threshold (CPT) measurement is a noninvasive, easy, and semi-objective method for determining sensory function using transcutaneous electrical stimulation. Previous studies have shown that CPT is determined by physical characteristics, such as sex, age, physical sites, and presence of neuropathy. Although the CPT reported in males is clearly higher than that in females, the reason for this difference remains unclear. This study investigates the cause of sex-based differences in CPT and suggests an adjustment method, which may suppress the sex difference in CPT.

MATERIALS AND METHODS

Electrical stimulation was applied with PainVision® via five sizes of circular surface electrodes. Seventy healthy participants were examined thrice under each electrode. The relationship among body water percentage, body fat percentage, and CPT was then analyzed.

RESULTS

CPT values are higher in males than that in females, with statistically significant sex differences with each electrode pairs (EL 1: p < 0.001; EL 2: p = 0.006; EL 3: p < 0.001; EL 4: p < 0.001; EL 5: p < 0.001). By adjusting for body fat percentage or body water percentage, the log-transformation values (CPT values) no longer exhibit sex differences with any electrode pairs (body fat: p = 0.09; body water: p = 0.08).

CONCLUSION

We conclude that sensitivity for perceiving electrical stimulation can be influenced by the subjects' characteristics, such as body fat or body water percentages.

Effect of Comorbid Post-Traumatic Stress Disorder and Panic Disorder on Defensive Responding

Abstract. Although panic disorder (PD) and post-traumatic stress disorder (PTSD) are characterized by heightened sensitivity to threat, no study to date has examined the effect of comorbid PD and PTSD on defensive responding. The present study probed startle eyeblink response to an acoustic probe in three groups of participants recruited from the community: (1) healthy individuals (n = 63), (2) individuals with PD without PTSD (n = 62), and (3) individuals with comorbid PD and PTSD (n = 24). Results indicated that PD individuals without PTSD exhibited greater sensitivity to threat relative to controls, and comorbid individuals displayed attenuated sensitivity to threat relative to PD individuals without PTSD (both ps < .05). The results are discussed in the context of the anxiety disorder spectrum, which postulates that anxiety disorders exist on a continuum spanning from specific/simple fear to broad distress, with defensive responding decreasing as distress increases.

Preliminary evidence that reactivity to uncertain threat is an endophenotype for alcohol use disorder

BACKGROUND

Having an exaggerated reactivity to threats that are uncertain (U-threat) may facilitate the initiation and maintenance of excessive alcohol use in some individuals. This abnormality may not just be a concomitant for alcohol use disorder (AUD), but also an endophenotype for AUD.

METHOD

The aim of the current study was therefore to provide a preliminary test of whether U-threat is an endophenotype for AUD using several of the endophenotype criteria outlined by Gottesman and Gould (2003). Specifically, the study examined whether heightened U-threat reactivity is evidenced in those with: 1) current AUD; 2) remitted AUD (early and sustained remission examined separately); and 3) at-risk for AUD by virtue of having a positive family history of AUD. Participants (N = 147) completed a well-validated threat-of-shock task and startle eyeblink potentiation was collected as an index of aversive responding. Individuals and all available first-degree family members were diagnosed using structured clinical interviews.

RESULTS

Individuals at-risk for AUD, with current AUD, and AUD in remission (both early and sustained) all displayed exaggerated reactivity to U-threat, but not predictable threat, compared with non-AUD controls. Moreover, there were no significant differences between the at-risk and any of the AUD groups indicating that exaggerated reactivity to U-threat is relatively state-independent and present regardless of current AUD disease status.

CONCLUSIONS

The findings together highlight that exaggerated reactivity to U-threat may be a promising endophenotype for AUD that can aid in the refinement of mechanistic AUD disease models.

Interaction of acupuncture treatment and manipulation laterality modulated by the default mode network

Appropriate selection of ipsilateral or contralateral electroacupuncture (corresponding to the pain site) plays an important role in reaching its better curative effect; however, the involving brain mechanism still remains unclear. Compared with the heat pain model generally established in previous study, capsaicin pain model induces reversible cutaneous allodynia and is proved to be better simulating aspects of clinical nociceptive and neuropathic pain. In the current study, 24 subjects were randomly divided into two groups with a 2 × 2 factorial design: laterality (ipsi- or contralateral side, inter-subject) × treatment with counter-balanced at an interval of one week (verum and placebo electroacupuncture, within-subject). We observed subjective pain intensity and brain activations changes induced by capsaicin allodynia pain stimuli before and after electroacupuncture treatment at acupoint LI4 for 30 min. Analysis of variance results indicated that ipsilateral electroacupuncture treatment produced significant pain relief and wide brain signal suppressions in pain-related brain areas compared with contralateral electroacupuncture. We also found that verum electroacupuncture at either ipsi- or contralateral side to the pain site exhibited comparable significant magnitudes of analgesic effect. By contrast, placebo electroacupuncture elicited significant pain reductions only on the ipsilateral rather than contralateral side. It was inferred that placebo analgesia maybe attenuated on the region of the body (opposite to pain site) where attention was less focused, suggesting that analgesic effect of placebo electroacupuncture mainly rely on the motivation of its spatial-specific placebo responses via attention mechanism. This inference can be further supported by the evidence that the significant interaction effect of manipulation laterality and treatment was exclusively located within the default mode network, including the bilateral superior parietal lobule, inferior parietal lobule, precuneus, and left posterior cingulate cortex. It is also proved that disruptions of the default mode network may account for the cognitive and behavioral impairments in chronic pain patients. Our findings further suggested that default mode network participates in the modulation of spatial-oriented attention on placebo analgesia as a mechanism underlying the degree to which treatment side corresponding to the pain.

Treatment response and central pain processing in Anterior Cutaneous Nerve Entrapment Syndrome: An explorative study

BACKGROUND

10-30% of chronic abdominal pain originates in the abdominal wall. A common cause for chronic abdominal wall pain is the Anterior Cutaneous Nerve Entrapment Syndrome (ACNES), in which an intercostal nerve branch is entrapped in the abdominal rectus sheath. Treatment consists of local anaesthetics and neurectomy, and is ineffective in 25% of cases for yet unknown reasons. In some conditions, chronic pain is the result of altered pain processing. This so-called sensitization can manifest as segmental or even generalized hyperalgesia, and is generally difficult to treat.

OBJECTIVE

The aim of this study was to assess pain processing in ACNES patients responsive and refractory to treatment by using Quantitative Sensory Testing, in order to explore whether signs of altered central pain processing are present in ACNES and are a possible explanation for poor treatment outcomes.

METHODS

50 patients treated for ACNES with locally orientated treatment were included. They were allocated to a responsive or refractory group based on their response to treatment. Patients showing an improvement of the Visual Analogue Scale (VAS) pain score combined with a current absolute VAS of <40mm were scored as responsive. Sensation and pain thresholds to pressure and electric skin stimulation were determined in the paravertebral bilateral ACNES dermatomes and at four control areas on the non-dominant side of the body, i.e. the musculus trapezius pars medialis, musculus rectus femoris, musculus abductor hallucis and the thenar. The ACNES dermatomes were chosen to signal segmental hyperalgesia and the sum of the control areas together as a reflection of generalized hyperalgesia. Lower thresholds were interpreted as signs of sensitized pain processing. To test for alterations in endogenous pain inhibition, a conditioned pain modulation (CPM) response to a cold pressor task was determined. Also, patients filled in three pain-related questionnaires, to evaluate possible influence of psychological characteristics on the experienced pain.

RESULTS

Patients refractory to treatment showed significantly lower pressure pain thresholds in the ACNES dermatomes and for the sum of as well as in two individual control areas. No differences were found between groups for electric thresholds or CPM response. Duration of complaints before diagnosis and treatment was significantly longer in the refractory compared to the responsive group, and refractory patients scored higher on the pain-related psychological surveys.

CONCLUSION AND IMPLICATIONS

In this hypothesis-generating exploratory study, ACNES patients refractory to treatment showed more signs of sensitized segmental and central pain processing. A longer duration of complaints before diagnosis and treatment may be related to these alterations in pain processing, and both findings could be associated with less effective locally orientated treatment. In order to validate these hypotheses further research is needed.

REGISTRATION NUMBER

NCT01920880 (Clinical Trials Register; http://www.clinicaltrials.gov).

Individual differences in pain sensitivity predict the experience of unfairness

Pain has shaped our evolutionary history, and pain-free experiences are critical for our health. There are, however, enormous individual differences in pain sensitivity, and the psychological consequences of this heterogeneity are only poorly understood. Here, we investigated whether individual differences in pain sensitivity predicted the experience of unfairness. We found that the magnitude of pain sensitivity correlated with the extent to which participants experienced unfairness. This association was due to the shared human alarm system of unfairness and pain sensitivity. This finding may elucidate mechanisms for producing a new and positive cycle of a healthy experience between fairness and feeling pain-free.

Towards an Objective Psychophysics of Pain

The limits of most sensory systems can now be routinely determined by objective detection-theory methods. The threshold of pain, however, is often thought to require more traditional methods that rely on a subject providing some estimate or description of what is perceived. The subject makes a measurement that cannot be contested and, in this sense, the methods are subjective. An experimental study of electrocutaneous stimuli showed how it is possible to interpret a traditional identification method and a category method in detection-theory terms. On this interpretation, these traditional methods yield results similar to a rating method of detection theory, a method that measures sensory resolution. However, the traditional methods give rise to additional judgmental variance not involved in standard detection-theory methods. They therefore do not provide a special insight into the experience of pain, and the extra variance they produce serves only to degrade, rather than to enhance, their usefulness.

Association between neural reactivity and startle reactivity to uncertain threat in two independent samples

Prior studies indicate that anxiety disorders are associated with heightened sensitivity to uncertain threat (U threat). Individual differences in reactivity to U threat have been measured in the laboratory with two methodologies-startle eyeblink potentiation and fMRI. While startle and fMRI are purported to relate to each other, very little research exists on whether individual differences in one measure are associated with individual differences in another and, thus, whether startle and fMRI capture shared mechanisms. Therefore, the current study was designed to investigate if and where in the brain measures of startle potentiation and fMRI BOLD signal correlate during response to U threat across two independent samples. Participants in both studies completed two threat anticipation tasks-once during collection of startle potentiation and once during fMRI. In Study 1 (n = 43), the startle and fMRI tasks both used electric shock as the threat. As an extension, in Study 2 (n = 38), the startle task used electric shock but the fMRI task used aversive images. Despite these methodological differences, greater startle potentiation to U threat was associated with greater dorsal anterior cingulate, caudate, and orbitofrontal cortex reactivity to U threat in both samples. The findings suggest that startle and fMRI measures of responding to U threat overlap, and points toward an integrated brain-behavior profile of aberrant U threat responding.

Reactivity to uncertain threat as a familial vulnerability factor for alcohol use disorder

BACKGROUND

When sober, problematic drinkers display exaggerated reactivity to threats that are uncertain (U-threat). Since this aversive affective state can be alleviated via acute alcohol intoxication, it has been posited that individuals who exhibit heightened reactivity to U-threat at baseline are motivated to use alcohol as a means of avoidance-based coping, setting the stage for excessive drinking. To date, however, no study has attempted to characterize the dispositional nature of exaggerated reactivity to U-threat and test whether it is a vulnerability factor or exclusively a disease marker of problematic alcohol use.

METHOD

The current investigation utilized a family study design to address these gaps by examining whether (1) reactivity to U-threat is associated with risk for problematic alcohol use, defined by family history of alcohol use disorder (AUD) and (2) reactivity to U-threat is correlated amongst adult biological siblings. A total of 157 families, and 458 individuals, participated in the study and two biological siblings completed a threat-of-shock task designed to probe reactivity to U-threat and predictable threat (P-threat). Startle potentiation was collected as an index of aversive responding.

RESULTS

Within biological siblings, startle potentiation to U-threat [intraclass correlation (ICC) = 0.35] and P-threat (ICC = 0.63) was significantly correlated. In addition, independent of an individuals' own AUD status, startle potentiation to U-threat, but not P-threat, was positively associated with risk for AUD (i.e. AUD family history).

CONCLUSION

This suggests that heightened reactivity to U-threat may be a familial vulnerability factor for problematic drinking and a novel prevention target for AUD.

Relationships among attention networks and physiological responding to threat

Although researchers have long hypothesized a relationship between attention and anxiety, theoretical and empirical accounts of this relationship have conflicted. We attempted to resolve these conflicts by examining relationships of attentional abilities with responding to predictable and unpredictable threat - related but distinct motivational process implicated in a number of anxiety disorders. Eighty-one individuals completed a behavioral task assessing efficiency of three components of attention - alerting, orienting, and executive control (Attention Network Test - Revised). We also assessed startle responding during anticipation of both predictable, imminent threat (of mild electric shock) and unpredictable contextual threat. Faster alerting and slower disengaging from non-emotional attention cues were related to heightened responding to unpredictable threat, whereas poorer executive control of attention was related to heightened responding to predictable threat. This double dissociation helps to integrate models of attention and anxiety and may be informative for treatment development.

Impact of Panic on Psychophysiological and Neural Reactivity to Unpredictable Threat in Depression and Anxiety

Exaggerated anxious responding to unpredictable threat (U-threat) is a core feature of panic disorder (PD). However, it is unknown whether this abnormality is specific to the diagnosis of PD or would manifest along a continuum of panic symptomatology (PS). Additionally, little is known about the neural processes underlying this abnormality among those high in PS. Finally, no studies have tested whether startle potentiation and limbic neural reactivity - commonly used indices of U-threat responsivity - are associated and therefore reflect common abnormalities. These questions were investigated in 42 adults with a range of PS. U-threat responding was measured twice during threat-of-shock - once with startle and once with functional magnetic resonance imaging (fMRI). As hypothesized, PS positively predicted startle potentiation and dACC reactivity to U-threat. Startle potentiation and dACC activation to U-threat were positively associated. These results suggest a biobehavioral profile of aberrant responding to U-threat associated with PS.

Mid-Air Tactile Stimulation Using Indirect Laser Radiation

In this paper, we demonstrate that a laser irradiated on a thin light-absorbing elastic medium attached on the skin can elicit a tactile sensation of mechanical tap. First, we present simulation results that show laser irradiation to the elastic medium creates inner elastic waves on the basis of thermoelastic effects and these elastic waves trigger the bending deformation of the medium, which then stimulates the skin. Second, we analyze the physical properties of the associated stimulus by measuring its force profile. Third, we identify the perceptual characteristics of the stimulus in comparison to those of mechanical and electrical stimuli by means of a perceptual experiment employing dissimilarity rating. All the evidence indicates that indirect laser radiation provides a sensation of short mechanical tap. Furthermore, little individual difference was observed in the results of the perceptual experiment. To the best of our knowledge, this study is the first in reporting the feasibility of indirect laser radiation for mid-air tactile rendering.

Association between problematic alcohol use and reactivity to uncertain threat in two independent samples

BACKGROUND

Recent laboratory studies have shown that acute alcohol intoxication selectively and effectively dampens aversive responding to uncertain threat. An emerging hypothesis is that individuals who exhibit heightened reactivity to uncertain threat may be especially motivated to use alcohol to dampen their distress, setting the stage for negative reinforcement processes to drive excessive alcohol use. However, no study to date has directly examined whether current problematic drinkers exhibit heightened reactivity to uncertain threat as would be expected.

METHODS

The present study was therefore designed to examine the association between current problematic alcohol use and reactivity to uncertain threat during sobriety in two, independent samples. In Study 1 (n=221) and Study 2 (n=74), adult participants completed the same well-validated threat-of-shock task which separately probes responses to temporally predictable and unpredictable threat. Startle potentiation was measured as an index of aversive responding. Problematic alcohol use was defined as number of binge episodes within the past 30days in Study 1 and total scores on a self-report measure of hazardous drinking in Study 2.

RESULTS

As hypothesized, across both studies greater levels of problematic drinking were associated with greater startle potentiation to unpredictable threat. In Study 2, hazardous drinking scores were also positively associated with startle potentiation to predictable threat.

CONCLUSIONS

The findings are notably consistent with the notion that heightened reactivity to uncertain threat is an important individual difference factor associated with the onset and/or maintenance of problematic drinking behaviors and may therefore be a novel prevention and intervention target.

Comparing the validity of informant and self-reports of personality using laboratory indices of emotional responding as criterion variables

Personality traits relate to risk for psychopathology and can inform predictions about treatment outcome. In an effort to obtain a comprehensive index of personality, informant reports of personality are sometimes obtained in addition to self-reports of personality. However, there is limited research comparing the validity of self- and informant reports of personality, particularly among those with internalizing psychopathology. This is important given that informants may provide an additional (and perhaps different) perspective on individuals' personality. The present study therefore compared how both reports of positive affectivity (PA) and negative affectivity (NA) relate to psychophysiological and subjective measures of emotional responding to positive and negative stimuli. Given that our sample (n = 117) included individuals with no history of psychopathology, as well as individuals with major depressive disorder (MDD) and/or panic disorder (PD), we were also able to explore whether these internalizing diagnoses moderated the association between personality reports and measures of emotional responding. Informant-reported PA predicted physiological responses to positive stimuli (but not negative). Informant-reported NA predicted physiological responses to negative stimuli (but not positive). Self-reported personality did not predict physiological responding, but did predict subjectively measured emotional responding (NA for negative responding, PA for positive responding). Diagnoses of internalizing psychopathology (PD or MDD) did not moderate these associations. Results suggest self- and informant reports of personality may each provide valid indices of an individual's emotional response tendencies, but predict different aspects of those tendencies.

The effects of electroacupuncture on analgesia and peripheral sensory thresholds in patients with burn scar pain

The aim of this study is to observe if the effects of electro-acupuncture (EA) on analgesia and peripheral sensory thresholds are transposable from the model of heat pain in volunteers to the clinical setting of burn scar pain. After severe burns, pathological burn scars (PPBS) may occur with excruciating pain that respond poorly to treatment and prevent patients from wearing their pressure garments, thereby leading to unesthetic and function-limiting scars. EA might be of greater benefit in terms of analgesia and functional recovery, should it interrupt this vicious circle by counteracting the peripheral hyperalgesia characterizing PPBS. Therefore we enrolled 32 patients (22 males/10 females) aged of 46±11 years with clinical signs of PPBS and of neuropathic pain despite treatment. The study protocol consisted in 3 weekly 30-min sessions of standardized EA with extra individual needles in accordance to Traditional Chinese Medicine, in addition of previous treatments. We assessed VAS for pain and quantitative sensory testing (QST) twice: one week before and one after protocol. QST measured electrical thresholds for non-nociceptive A-beta fibers, nociceptive A-delta and C fibers in 2 dermatomes, respectively from the PPBS and from the contralateral pain-free areas. Based on heat pain studies, EA consisted in sessions at the extremity points of the main meridian flowing through PPBS (0.300s, 5Hz, sub noxious intensity, 15min) and at the bilateral paravertebral points corresponding to the same metameric level, 15min. VAS reduction of 3 points or below 3 on a 10 points scale was considered clinically relevant. Paired t-test compared thresholds (mean [SD]) and Wilcoxon test compared VAS (median [IQR]) pre and after treatment, significant p<0.05. The reduction of VAS for pain reached statistical but not clinical relevance (6.8 [3] vs. 4.5 [3.6]). This was due to a large subgroup of 14 non-responders whose VAS did not change after treatment (6.6 [2.7] vs. 7.2 [3.8]). That subgroup exhibited significant differences in sensory thresholds when compared to the 18 responders (VAS from 7 [3] to 3 [1]). First, responders' thresholds for A-delta and C fibers in the PPBS area were significantly lower than those in the pain-free area before treatment but corrected after acupuncture (from respectively 60 [30] and 63 [10]% to 91 [11] and 106 [36]%). That might account for a nociceptive hypersensitivity in the PPBS that corrected after treatment. On the contrary, in non-responders nociceptive thresholds were similar in both the PPBS and the pain-free areas before treatment and did not change after EA. However, absolute values for thresholds in the pain-free areas where significantly lower for non-responders than for responders. The fact that non-responders had significant pain scores while presenting with lowered nociceptive thresholds even in the pain-free areas might evoke the possibility of a generalized supra-spinal hyperalgesia. The fact that acupuncture did not correct the pain nor the nociceptive thresholds in this subgroup requires further investigation. We also observed a statistically and clinically relevant reduction in VAS for pruritus for all patients - even those from the subgroup of non-responders to pain - that is worth to be mentioned and requires further studies to be confirmed. This observational study is the first that confirms the effects of acupuncture on analgesia and nociceptive thresholds in the clinical setting of burn pain only for patients presenting with a burn-localized but not a generalized hyperalgesia.

Time course of threat responding in panic disorder and depression

Heightened sensitivity to threat is a characteristic feature of panic disorder (PD). It is also a factor that is considered to be central to PD but not major depressive disorder (MDD) – a related disorder that commonly co-occurs with PD. However, sensitivity to threat is a broad construct and it is unclear whether individuals with PD exhibit heightened initial threat reactivity, impairments in modulating their threat responding over time, or both. It is also unclear how these different facets of threat responding apply to predictable and/or unpredictable threat. The aim of the current study was to examine whether there are differences in initial threat reactivity and the time course of threat responding during predictable and unpredictable threat-of-shock in 186 adults with: 1) current PD and no history of depression (i.e., PD-only), 2) current MDD and no history of an anxiety disorder (i.e., MDD-only), 3) current comorbid PD and MDD, or 4) no lifetime history of psychopathology (i.e., controls). Threat responding was assessed using an electromyography startle paradigm. Relative to controls, individuals in the three psychopathology groups exhibited heightened initial threat reactivity to predictable and unpredictable threat and did not differ from each other. Multilevel mixed model analyses indicated that those with PD evidenced less of a decline over time in startle responding during unpredictable threat relative to those without PD. Those with MDD displayed a greater slope of decline in startle responding during predictable threat compared with those without MDD. The pattern of results suggests that there may be conceptual differences between measures of initial threat reactivity and time course of threat responding. Moreover, time course of threat responding, not initial threat reactivity, may differentiate PD from MDD.

Aversive responding to safety signals in panic disorder: the moderating role of intolerance of uncertainty

An inability to inhibit aversive responding during conditions that signal safety may be a core dysfunction associated with anxiety disorders. However, there has been inconsistent evidence as to whether individuals with panic disorder (PD) exhibit aversive responding during safety signals. It is therefore possible that only certain subgroups of PD patients, particularly those with high levels of intolerance of uncertainty (IU), evidence this type of abnormal responding. The aim of the current study was to examine whether IU moderates the association between PD and startle potentiation during (a) safety and (b) threat periods during a threat-of-shock task. Participants included 172 adults, 74 of which had current diagnoses of PD. Results indicated that at high levels of IU, PD was associated with greater startle potentiation during safety. At low levels of IU, PD was not associated with startle potentiation during safety. IU did not moderate the effect of PD on threat responding. These results suggest that PD patients with high levels of IU fail to inhibit aversive responding during safety, possibly due to a tendency to interpret distal threat as distressing.

Are individual differences in appetitive and defensive motivation related? A psychophysiological examination in two samples

Appetitive and defensive motivation account for a good deal of variance in personality and mental health, but whether individual differences in these systems are correlated or orthogonal has not been conclusively established. Previous investigations have generally relied on self-report and have yielded conflicting results. We therefore assessed the relation between psychophysiological indices of appetitive and defensive motivation during elicitation of these motivational states: specifically, frontal electroencephalogram asymmetry during reward anticipation and startle response during anticipation of predictable or unpredictable threat of shock. Results in a sample of psychopathology-free community members (n=63), an independent sample of undergraduates with a range of internalising symptoms (n=64), and the combination of these samples (n=127) revealed that differences in responding to the two tasks were not significantly correlated. Average coefficients approached zero in all three samples (community: .04, undergraduate: -.01, combined: .06). Implications of these findings for research on normal and abnormal personality are discussed.

Startle response to unpredictable threat in comorbid panic disorder and alcohol dependence

BACKGROUND

Although the adverse consequences of comorbid panic disorder (PD) and alcohol dependence (AD) are well-established, relatively little is known about the mechanisms underlying their co-occurrence. Several researchers have postulated that alcohol's ability to dampen response to unpredictable threat may be an important motivational factor in comorbid PD and AD. To date, no research has examined these processes using a clinical sample and it is unclear whether individuals with PD and AD evidence different reactivity to unpredictable threat relative to individuals with PD-only.

METHODS

The aim of the current study was to examine differences in aversive responding during predictable and unpredictable threat-of-shock in three groups of individuals with: (1) current PD and remitted AD (PD and AD), (2) current PD but no lifetime diagnosis of AD (PD-only), and (3) no lifetime diagnoses of PD or AD (controls). Aversive responding was assessed using a well-established electromyography (EMG) startle paradigm.

RESULTS

Results indicated that PD and AD individuals evidenced greater startle potentiation during unpredictable (but not predictable) threat relative to controls and PD-only individuals (who did not differ).

CONCLUSIONS

These findings suggest that heightened reactivity to unpredictable threat may be an important process in PD and AD comorbidity and a possible key motivational factor underlying engagement in alcohol use.

Characteristics of electronic training collars for dogs

A wide range of electronic dog training collars (e-collars) is available in the UK, but information enabling purchasers to compare the important characteristics of these collars is not available. In this research, the electrical characteristics of 13 e-collar models were examined, and an approach to ranking the strength of the electrical stimuli was developed. To achieve this, the electrical impedance of dogs' necks were measured so that e-collars could be tested under realistic conditions. This impedance was found to be about 10 kΩ for wet dogs and 640 kΩ for dry dogs. Two replicates of eight e-collar models and single copies of a further five models were then examined. The stimuli generated by these collars comprised sequences of short high-voltage pulses. There were large differences between e-collar models in the energy, peak voltage, number of pulses and duration of the pulses, but little variation between the replicates. The peak voltage varied with the impedance, from 6000V at an impedance of 500 kΩ to 100V at 5 kΩ. The highest voltages were generated for a few millionths of a second. Stimulus energy levels at the maximum strength setting with a 50 kΩ load ranged from 3.3 mJ to 287 mJ. A stimulus strength ranking indicator was then developed to enable the strengths of e-collars with diverse electrical characteristics to be ranked. This ranking shows a wide range in the stimulus strengths of collars, and that the relationships between 'momentary' and 'continuous' stimuli for various models differ significantly.

Relation between Respiratory Sinus Arrythymia and Startle Response during Predictable and Unpredictable Threat

Research suggests that lower respiratory sinus arrhythmia (RSA) is associated with greater aversive responding. One physiological indicator of aversive responding is startle potentiation. While a few studies have demonstrated an inverse association between RSA and startle potentiation, no study to date has distinguished whether this relation is similar for predictable versus unpredictable aversive stimuli. This is an important distinction, given that degree of predictability has been shown to be an important determinant of aversive responding. The present study examined whether resting RSA was associated with startle eye blink responding during predictable and unpredictable threat of electric shock. Resting RSA was collected during a 6-minute seated baseline phase at the beginning of the experimental session. Participants then completed a computerized startle task in which predictable and unpredictable shocks were administered. Results indicated that lower resting RSA was associated with greater startle potentiation during unpredictable threat, but not during predictable threat. These findings are consistent with a growing body of literature suggesting that individual differences in RSA are associated with aversive responding, and extend previous work by suggesting that RSA may be more robustly associated with a heightened sensitivity to unpredictable threat. This pattern of results may have implications for the understanding of pathological anxiety given that individuals with anxiety disorders typically exhibit low RSA and heightened responding during unpredictable threat.

A psychophysiological investigation of threat and reward sensitivity in individuals with panic disorder and/or major depressive disorder

Heightened sensitivity to threat and reduced sensitivity to reward are potential mechanisms of dysfunction in anxiety and depressive disorders, respectively. However, few studies have simultaneously examined whether these mechanisms are unique or common to these disorders. In this study, sensitivity to predictable and unpredictable threat (measured by startle response during threat anticipation) and sensitivity to reward (measured by frontal electroencephalographic [EEG] asymmetry during reward anticipation) were assessed in 4 groups (N = 191): those with (1) panic disorder (PD) without a lifetime history of depression, (2) major depression (MDD) without a lifetime history of an anxiety disorder, (3) comorbid PD and MDD, and (4) controls. General distress/negative temperament (NT) was also assessed via self-report. Results indicated that PD (with or without comorbid MDD) was uniquely associated with heightened startle to predictable and unpredictable threat, and MDD (with or without comorbid PD) was uniquely associated with reduced frontal EEG asymmetry. Both psychophysiological measures of threat and reward sensitivity were stable on retest approximately 9 days later in a subsample of participants. Whereas the comorbid group did not respond differently on the tasks relative to the PD-only and MDD-only groups, they did report greater NT than these 2 groups (which did not differ from each other). Results suggest that heightened sensitivity to threat and reduced sensitivity to reward may be specific components of PD and MDD, respectively. In addition, relative to noncomorbid depression and PD, comorbid MDD and PD may be characterized by heightened NT, but not abnormal levels of these "specific" components.

Does past pain influence current pain: biological and psychosocial models of sex differences

Previous studies have generally indicated sizeable sex differences for both laboratory pain reactivity and clinical pain reports. Numerous biological and psychosocial models have been invoked to account for these findings, but the laboratory and clinical findings have generally been examined in isolation. This paper reviews data which show a relationship between past clinical pain experiences and current responses to experimentally induced pain. Individuals with a greater pain history tend to show lower pain tolerance. Since women often have high pain experience levels and lower pain tolerance, one might ask whether the two factors are related. We review several models, based upon concepts of neonatal differences in pain reactivity, hypervigilance following early pain experiences, and concepts of peripheral and central sensitization or plasticity which might help to bridge the gap between clinical and experimental findings.

The impact of language on the expression and assessment of pain in children

This paper focuses on the importance of language in the expression of pain. Variation in definitions of pain is presented, together with a review of the evidence examining the impact language may have on the way pain is expressed linguistically. The implications for conducting research with children who speak different languages are explored. Strategies such as using non-linguistic methods of communication, additional time required for conducting interviews and the inclusion of research team members from the same ethnic or linguistic background are presented.

Effects of predictability of shock timing and intensity on aversive responses

An important characteristic of aversive stimuli that determines emotional responses is whether the stimuli are predictable. Human laboratory studies in this area have typically operationalized predictability as being able to predict the occurrence of aversive events, but animal studies suggest that being able to predict other characteristics of the stimuli may also play a role in aversive responding. To examine this, the present study examined two characteristics: the timing and intensity of aversive stimuli. Specifically, participants were randomly assigned to receive shocks that were either predictable or unpredictable in terms of when they would occur (timing) and/or their intensity. Indicators of aversive emotional responses were EMG startle responses and subjective anxiety ratings. Results revealed that aversive responding was elevated for unpredictable timing and intensity suggesting that the predictability of both characteristics play a role in aversive responding (though the effects for timing were stronger). In sum, the anxiogenic effects of unpredictability may generalize to situations beyond unpredictable timing.

Gender role expectations of pain is associated with pain tolerance limit but not with pain threshold

Gender role expectations of pain (GREP) was suggested to predict sex differences in pain perception. Our aim was to explore sex differences in GREP and investigate its relationship with heat-pain threshold (HPT) and heat-pain tolerance limit (HPTL). University students (115 males, 134 females) filled the GREP questionnaire. HPT and HPTL were measured in a sample of 72 students. Additionally, GREP values of the present sample were compared with those of the original, American sample to explore possible cultural effects. Both males and females perceive themselves (and their own sex in general) to be less sensitive to pain and less willing to report of pain than the opposite sex. Males perceived themselves and other men, to endure pain relatively similar to women whereas females perceived themselves and other women as less endurable to pain than men. HPT was similar for the two sexes but males had higher HPTL than females. Within each sex, HPTL correlated mainly with self's perception of pain sensitivity. The American and Israeli samples differed in that Israeli males and females presented stronger stereotypical views towards same and opposite sexes. Both males and females held stereotypical "macho" attitude towards themselves with regard to pain sensitivity and willingness to report of pain however only females held stereotypical, "macho" attitude towards themselves with regard to pain endurance. The sex differences in GREP and in HPTL and the correlations between GREP items and experimental thresholds suggest that the relationship between GREP and experimental pain is complex and sex-specific. It also appears that GREP is affected by culture.

Sex differences in nociceptive withdrawal reflex and pain perception

Experimentally induced pain often reveals sex differences, with higher pain sensitivity in females. The degree of differences has been shown to depend on the stimulation and assessment methods. Since sex differences in pain develop anywhere along the physiological and psychological components of the nociceptive system, we intended to compare the nociceptive flexion reflex (NFR) as a more physiological (spinal) aspect of pain procession to the verbal pain report of intensity and unpleasantness as the more psychological (cortical) aspect. Twenty female and twenty male healthy university students were investigated by use of nociceptive flexion reflex threshold (staircase method) after electrical stimulation of the N. suralis. Furthermore, we assessed supra-threshold reflex responses (latency, amplitude and area) by applying 10 stimuli 5 mA above reflex threshold. Following each stimulation, the subjects provided pain ratings of intensity and unpleasantness on a visual analogue scale. Females exhibited marked lower nociceptive flexion reflex thresholds than males, while the supra-threshold reflex response tailored to the individual reflex threshold did not show any significant differences. The verbal pain ratings, corrected for NFR threshold, were not found to differ significantly. The large sex differences in nociception that were present in NFR threshold but not in the pain ratings corroborate the hypothesis that spinal processes contribute substantially to sex differences in pain procession.

Comparison of pain thresholds and pain tolerance levels between Middle Easterners and Swedes and between genders

OBJECTIVE

This study evaluates the presence of culture and gender differences in pain thresholds and pain tolerance levels between Middle Easterners and Swedes.

METHODS

Sixty-four healthy individuals, 32 Middle Easterners (16 men and 16 women, mean age: 24.6 +/- 3.4 years) and 32 Swedes (16 men and 16 women, mean age: 24 +/- 3.5 years) participated in the study. Three experimental pain tests were conducted in each participant. Pain thresholds and pain tolerance levels were measured using an algometer (mechanical stimulus), the PainMatcher((R)) (electric stimulus) and cold pressor test (thermal stimulus).

RESULTS

While no significant differences in pain thresholds were observed between Middle Easterners and Swedes in algometer and cold pressor tests, differences in pain tolerance levels were significant (P < 0.01 for both tests). All between-culture differences in pain perception, pain threshold and pain tolerance level were non-significant when measured with the PainMatcher. Significant between-gender differences were observed only in pain threshold with the PainMatcher (P < 0.05) and in pain tolerance level with the algometer (P < 0.01) and the PainMatcher (P <0.001).

CONCLUSION

This study found significant differences in two out of three pain tolerance level tests - but not pain threshold tests - between the Middle Eastern and Swedish cultures and between genders. These differences were more pronounced between Middle Eastern and Swedish men than between Middle Eastern and Swedish women. Gender differences were more pronounced within the Swedish than the Middle Eastern culture. These findings indicate that culture and gender influence pain experience.

Ethnic identity predicts experimental pain sensitivity in African Americans and Hispanics

The aim of this study was to examine experimental pain sensitivity in three ethnic groups, African Americans, Hispanic Americans and non-Hispanic White Americans, and to determine whether ethnic identity is differentially associated with pain sensitivity across ethnic groups. Participants included sixty-three African American, sixty-one Hispanic and eighty-two non-Hispanic white participants who were assessed using three experimental pain measures: thermal, cold-pressor and ischemic. Participants' ethnic identity was assessed using the Multi-group Ethnic Identity Measure (MEIM). Ethnic group differences in pain responses were observed, with African American and Hispanic subjects showing lower cold and heat pain tolerances than non-Hispanic White Americans. In addition, pain range (i.e. tolerance-threshold) was computed for heat, cold and ischemic pain, and the two minority groups again had lower values compared to non-Hispanic White Americans. Ethnic identity was associated with pain range only for African American and Hispanic groups. Statistically controlling for ethnic identity rendered some of the group differences in pain range non-significant. These findings indicate that ethnic identity is associated with pain sensitivity in ethnic minority groups, and may partially mediate group differences in pain perception. The results of the present investigation provide evidence of ethnic group differences in responses to experimental pain across multiple noxious stimuli, with both minority groups exhibiting greater sensitivity to laboratory evoked pain compared to non-Hispanic White Americans.

Role of gender norms and group identification on hypothetical and experimental pain tolerance

Previous research indicates that men typically tolerate more pain in experimental settings than women. One likely explanation for these group differences in pain tolerance is conformity to traditional, gender group social norms (i.e., the ideal man is masculine and tolerates more pain; the ideal woman is feminine and tolerates less pain). According to self-categorization theory, norms guide behavior to the degree that group members adopt the group identity. Therefore, high-identifying men are expected to conform to gender norms and tolerate more pain than high-identifying women who conform to different gender norms as a guide for their behavior. We conducted two studies to investigate whether gender group identification moderates individuals' conformity to pain tolerance and reporting norms. In the first study, participants indicated their gender identification and expected tolerance of a hypothetical painful stimulus. As anticipated, high-identifying men reported significantly greater pain tolerance than high-identifying women. No differences existed between low-identifying men and women. To determine if self-reported pain tolerance in a role-playing scenario corresponds to actual pain tolerance in an experimental setting, the second study examined pain tolerance to a noxious stimulus induced by electrical stimulation of the index finger. The experimental outcome revealed that high-identifying men tolerated more painful stimulation than high-identifying women. Further, high-identifying men tolerated more pain than low-identifying men. These results highlight the influence of social norms on behavior and suggest the need to further explore the role of norms in pain reporting behaviors.

Multi-modal and tissue-differentiated experimental pain assessment: reproducibility of a new concept for assessment of analgesics

Experimental pain models for assessment of analgesic effect needs to be reproducible, valid and responding in a uniform way to changes in pain level. The pain system differs in various tissue types and analgesics may have different effects in different tissues. This study assessed the reproducibility of an experimental model using mechanical, thermal and electrical stimulations. Pain was evoked in three tissues: Skin, muscle and viscera. Pain was evoked and assessed in 24 healthy volunteers. The experiment was repeated three times with 30 min. intervals and twice with a weekly interval. Systematic bias, intra-class correlation (ICC) and coefficient of variation (CV) and valid sample sizes for analgesic testing were assessed. The model proved to be feasible. Most tests were unbiased, showing stable means except for the mechanical and thermal stimulation in viscera, which showed decreasing pain thresholds when the tests were repeated with 30 min. intervals. Generally the pain tests showed relatively high CV (mean 71%, range 8-145%). The pain tests showed high ICC's (>0.80) when repeated on the same day. When the tests were repeated with an interval of one week, ICC was smaller (mean 0.79 range 0.49-0.96). This means that these tests are useful for analgesic testing recruiting useful sample sizes in a crossover (mean 31 range 2-84) and a parallel study (mean 59 range 3-164) design. Application of this experimental pain model in a cross-over study design with appropriate base-line recordings offers a unique opportunity of revealing analgesic effects on pain arising from different tissues.

Influence of age and gender on the jaw-stretch and blink reflexes

The aim of this study is to investigate the influence of age and gender on jaw-stretch and blink reflexes (BR). Thirty "young" (26.5+/-0.7 years) and thirty "old" (47.8+/-1.8 years) healthy adults were included. Short-latency stretch reflex responses were evoked in the masseter and temporalis muscles by fast jaw-stretches, and BR in orbicularis oculi muscle were evoked by painful electrical pulses (0.5 ms duration), delivered by a concentric electrode placed on the left lower forehead close to the supraorbital foramen. For the jaw-stretch reflex, the pre-stimulus EMG activity in the old subjects was significantly lower than that of the young subjects in the right and left masseter and temporalis muscles (P<0.006), whereas there was no difference in the results between males and females. The normalized peak-to-peak amplitude of the EMG in the left masseter and left and right temporalis muscles was significantly lower in the old subjects compared with the young subjects (P<0.02). Females had significantly higher normalized peak-to-peak EMG amplitudes compared with males in the right masseter and left temporalis muscles (P<0.05). The old subjects had significantly lower root mean square (RMS) (P=0.01) and average (P<0.02) BR values in the right and left orbicularis oculi muscles, and lower area under the curve (AUC) (P=0.02) values in the left orbicularis oculi muscle compared with the young subjects. Female subjects had significantly lower AUC (P=0.02) in the left orbicularis oculi muscle compared with males. The old subjects had significantly later offset (P<0.003) and longer duration (P<0.001) in the left orbicularis oculi compared with the young subjects. The results of the present study demonstrated a significant effect of both age and gender on stretch and BR and suggested that these variables should be taken into consideration in the interpretation of brainstem reflexes in basic and clinical studies.

Chronic pancreatitis patients show hyperalgesia of central origin: a pilot study

BACKGROUND

The pain of chronic pancreatitis remains challenging to manage, with treatment all too often being unsuccessful. A main reason for this is lacking understanding of underlying mechanisms of chronic pain in these patients.

AIM

To document, using somatic quantitative sensory testing, changes in central nervous system processing (neuroplasticity) associated with chronic pancreatitis pain and thus gain insight into underlying pain mechanisms.

PATIENTS AND METHODS

We studied 10 chronic pancreatitis patients on stable opioid analgesic medication. Ten matched surgical patients without pain served as controls. Pain verbal numeric rating scores (NRS) and thresholds to electric skin stimulation and pressure pain were measured in dermatomes T10 (pancreatic area), C5, T4, L1 and L4.

RESULTS

The pancreatitis patients had a median NRS pain score of 5 (range 3-8). Electric sensation and pain thresholds were significantly increased in the pancreatic region, tending to be more so in female pancreatitis patients. Pressure pain thresholds were significantly lower in pancreatitis patients than in controls, with men tending towards greater generalised relative hyperalgesia than women.

CONCLUSIONS

Chronic pancreatitis patients show pronounced generalised deep hyperalgesia that is present despite opioid therapy. These signs, consistent with central sensitisation, appear relatively more prominent in men than women. There is also evidence suggesting that women may have a better segmental inhibitory response than men, possibly explaining their relatively less prominent generalised deep tissue hyperalgesia compared to men.

Mechanisms of pain associated with internal defibrillation shocks: Results of a randomized study of shock waveform

BACKGROUND

Shock pain has limited the acceptance of the implantable atrial cardioverter and is a complication of ventricular implantable cardioverter-defibrillator therapy. Rounding off of the peak of a shock waveform reduces pain. Whether the pain reduction results from reduction in the peak voltage or from the rounding has not been established. In other words, does reducing the extreme dV/dt (voltage derivative) of the conventional truncated exponential capacitive discharge waveform reduce pain?

OBJECTIVES

The purpose of this study was to compare the relative contributions of peak voltage and waveform shape to pain.

METHODS

We compared rounded and conventional waveforms with equal peak voltages. Eighty-five shocks of 50 to 500 V were delivered to 10 patients requiring atrial cardioversion for persistent atrial fibrillation. The patient touched an analog pain scale (0-15 cm) and orally reported a pain score on a scale from 0 to 5. An observer scored thoracic contractions on a scale from 0 to 5.

RESULTS

No differences between the rounded and conventional waveform on any scale were noted for either univariate or multivariate analyses. However, all three response scales were strongly predicted by voltage with r(2) = 0.77 (oral), r(2) = 0.86 (analog), and r(2) = 0.85 (contraction) after correcting for patient variability and including a log voltage term.

CONCLUSIONS

Patient pain perception was determined primarily by waveform peak voltage and not by the rounding, per se.

Personality characteristics as differential variables of the pain experience

This study analyzes the relationships between neuroticism, extroversion, age, and sex and the intensity of perceived pain and the coping strategies used. We worked with a sample of 96 patients with chronic pain. The assessment tools were the following: the Vanderbilt Pain Management Inventory, a Spanish version of the McGill Pain Questionnaire, and the Eysenck Personality Inventory. The hypothetical model establishes positive relationships between neuroticism, the use of passive coping strategies, and the intensity of pain. On the other hand, extraversion is expected to be positively related to the use of active coping strategies and negatively related to the perceived intensity of pain. The results support the hypotheses formulated regarding the effects of the variables neuroticism and extraversion. Age is negatively related to active coping strategies and pain intensity. Men use more active strategies than women, while the latter have a greater perception of pain.