Influence of gender and hemispheric lateralization on heat pain perception in major depression

TMS in combination with a pain directed intervention for the treatment of fibromyalgia - A randomized, double-blind, sham-controlled trial

BACKGROUND

Fibromyalgia Syndrome (FMS) is a highly prevalent condition, that causes chronic pain and severe reduction in quality of life and productivity, as well as social isolation. Despite the significant morbidity and economic burden of FMS, current treatments are scarce.

OBJECTIVE

To investigate whether stimulation of ACC -mPFC activity by dTMS enhances a pain-directed psychotherapeutic intervention.

METHODS

19 FMS patients were randomised to receive either 20 sessions of dTMS or sham stimulation, each followed by a pain-directed psychotherapeutic intervention. With the H7 HAC coil or sham stimulation, we targeted the ACC -mPFC; specific brain areas that play a central role in pain processing. Clinical response to treatment was assessed with the McGill Pain Questionnaire Short Form (SF-MPQ), the Visual Analogue Fibromyalgia Impact Questionnaire, the Brief Pain Inventory questionnaire, and the Hamilton Depression Rating Scale.

RESULTS

DTMS treatment was safe and well tolerated by FMS patients. A significant decrease in the combined sensory and affective pain dimensions was specifically demonstrated in the dTMS cohort, as measured by the SF-MPQ (Significant group × time interaction [F(2, 32) = 3.51, p < .05,ηp2 = 0.18]; No significant changes were found in depressive symptoms in both the dTMS and sham groups.

CONCLUSION

Our results suggest that a course of dTMS combined with a pain-directed psychotherapeutic intervention can alleviate pain symptoms in FMS patients. Beyond clinical possibilities, future studies are needed to substantiate the innovative hypothesis that it is not dTMS alone, but rather dTMS-induced plasticity of pain-related networks, that enables the efficacy of pain-directed psychotherapeutic interventions.

How does feeling pain look like in depression: A review of functional neuroimaging studies

INTRODUCTION

Major Depression Disorder (MDD) and pain appear to be reciprocal risk factors and sharing common neuroanatomical pathways and biological substrates. However, the role of MDD on pain processing remains still unclear. Therefore, this review aims to focus on the effect of depression on pain anticipation, and perception, before and after treatment, through functional magnetic resonance imaging (fMRI).

METHODS

A bibliographic search was conducted on PubMed, Scopus and Web of Science, looking for fMRI studies exploring pain processing in MDD patients.

RESULTS

Amongst the 602 studies retrieved, 12 met the inclusion criteria. In terms of pain perception, studies evidenced that MDD patients generally presented increased activation in brain regions within the prefrontal cortex, insula and in the limbic system (such as amygdala, hippocampus) and occipital cortex. The studies investigating the effect of antidepressant treatment evidenced a reduced activation in areas such as insula, anterior cingulate, and prefrontal cortices. In terms of pain anticipation, contrasting results were evidenced in MDD patients, which presented both increased and decreased activity in the prefrontal cortex, the insula and the temporal lobe, alongside with increased activity in the anterior cingulate cortex, the frontal gyrus and occipital lobes.

LIMITATIONS

The small number of included studies, the heterogeneous approaches of the studies might limit the conclusions of this review.

CONCLUSIONS

Acute pain processing in MDD patients seems to involve numerous and different brain areas. However, more specific fMRI studies with a more homogeneous population and rigorous approach should be conducted to better highlight the effect of depression on pain processing.

Selective breeding of rats for high (HAB) and low (LAB) anxiety-related behaviour: A unique model for comorbid depression and social dysfunctions

Animal models of selective breeding for extremes in emotionality are a strong experimental approach to model psychopathologies. They became indispensable in order to increase our understanding of neurobiological, genetic, epigenetic, hormonal, and environmental mechanisms contributing to anxiety disorders and their association with depressive symptoms or social deficits. In the present review, we extensively discuss Wistar rats selectively bred for high (HAB) and low (LAB) anxiety-related behaviour on the elevated plus-maze. After 30 years of breeding, we can confirm the prominent differences between HAB and LAB rats in trait anxiety, which are accompanied by consistent differences in depressive-like, social and cognitive behaviours. We can further confirm a single nucleotide polymorphism in the vasopressin promotor of HAB rats causative for neuropeptide overexpression, and show that low (or high) anxiety and fear levels are unlikely due to visual dysfunctions. Thus, HAB and LAB rats continue to exist as a reliable tool to study the multiple facets underlying the pathology of high trait anxiety and its comorbidity with depression-like behaviour and social dysfunctions.

Altered physical pain processing in different psychiatric conditions

Several reports indicate either increased or decreased pain sensitivity associated with psychiatric disorders. Chronic pain is highly prevalent in many of these conditions. We reviewed the literature regarding experimental pain sensitivity in patients with major depression, bipolar disorder, posttraumatic stress disorder (PTSD), generalized anxiety disorder, panic disorder, obsessive-compulsive disorder and schizophrenia. Electronic searches were performed to identify studies comparing experimental pain in patients with these conditions and controls. Across 31 depression studies, reduced pain threshold was noted except for ischemic stimuli, where increased pain tolerance and elevated sensitivity to ischemic pain was observed. A more pervasive pattern of low pain sensitivity was found across 20 schizophrenia studies. The majority of PTSD studies (n = 20) showed no significant differences compared with controls. The limited number of bipolar disorder (n = 4) and anxiety (n = 9) studies precluded identification of clear trends. Wide data variability was observed. Awareness of psychiatric patients' pain perception abnormalities is needed for active screening and addressing physical comorbidities, in order to enhance quality of life, life expectancy and mental health.

Attentional Biases Towards Body Expressions of Pain in Men and Women

This study investigated whether there are gender differences in attention to bodily expressions of pain and core emotions. Three experiments are reported using the attentional dot probe task. Images of men and women displaying bodily expressions, including pain, were presented. The task was used to determine whether participants' attention was drawn towards or away from target expressions. Inconsistent evidence was found for an attentional bias towards body expressions, including pain. While biases were affected by gender, patterns varied across the Experiments. Experiment 1, which had a presentation duration of 500 ms, found a relative bias towards the location of male body expressions compared to female expressions. Experiments 2 and 3 varied stimulus exposure times by including both shorter and longer duration conditions (e.g., 100 vs. 500 vs. 1250 ms). In these experiments, a bias towards pain was confirmed. Gender differences were also found, especially in the longer presentation conditions. Expressive body postures captured the attention of women for longer compared to men. These results are discussed in light of their implications for why there are gender differences in attention to pain, and what impact this has on pain behaviour. PERSPECTIVE: We show that men and women might differ in how they direct their attention towards bodily expressions, including pain. These results have relevance to understanding how carers might attend to the pain of others, as well as highlighting the wider role that social-contextual factors have in pain.

Differential neural processing of unpleasant sensory stimulation in patients with major depression

An altered processing of negative salient stimuli has been suggested to play a central role in the pathophysiology of major depression (MD). Besides negative affective and social stimuli, physical pain as a subtype of negative sensory stimulation has been investigated in this context. However, the few neuroimaging studies on unpleasant sensory stimulation or pain processing in MD report heterogeneous findings. Here, we investigated 47 young females, 22 with MD and 25 healthy controls (HC) using fMRI (3.0 T). Four levels of increasingly unpleasant electrical stimulation were applied. Ratings of stimulus intensity were assessed by a visual analogue scale. fMRI-data were analyzed using a 2 × 4 ANOVA. Behavioral results revealed no group differences regarding accuracy of unpleasant stimulation level ratings and sensitivity to stimulation. Regarding neural activation related to increasing levels of unpleasant stimulation, we observed increasing activation of brain regions related to the pain and salient stimulus processing corresponding to increasingly unpleasant stimulation in controls. This modulation was significantly smaller in MD compared to controls, particularly in the dorsal anterior cingulate cortex, the somatosensory cortex, and the posterior insula. Overall, brain regions associated with the processing of unpleasant sensory stimulation, but also associated with the salience network, were highly reactive but less modulated in female patients with MD. These results support and extent findings on altered processing of salience and of negative sensory stimuli even of a non-painful quality in female patients with MD.

Emotional Components of Pain Perception in Borderline Personality Disorder and Major Depression-A Repetitive Peripheral Magnetic Stimulation (rPMS) Study

Various studies suggested alterations in pain perception in psychiatric disorders, such as borderline personality disorder (BPD) and major depression (MD). We previously investigated affective components of pain perception in BPD compared to healthy controls (HC) by increasing aversive stimulus intensities using repetitive peripheral magnetic stimulation (rPMS) and observed alterations in emotional rather than somatosensory components in BPD. However, conclusions on disorder specific alterations in these components of pain perception are often limited due to comorbid depression and medication in BPD. Here, we compared 10 patients with BPD and comorbid MD, 12 patients with MD without BPD, and 12 HC. We applied unpleasant somatosensory stimuli with increasing intensities by rPMS and assessed pain threshold (PT), cutaneous sensation, emotional valence, and arousal by a Self-Assessments Manikins scale. PTs in BPD were significantly higher compared to HC. The somatosensory discrimination of stimulus intensities did not differ between groups. Though elevated rPMS intensities led to increased subjective aversion and arousal in MD and HC, these emotional responses among intensity levels remained unchanged in BPD. Our data give further evidence for disorder-specific alterations in emotional components of pain perception in BPD with an absent emotional modulation among varying aversive intensity levels.

Body Image Relates to Exercise-Induced Antinociception and Mood Changes in Young Adults: A Randomized Longitudinal Exercise Intervention

Background: An important motivation for adolescents and young adults to engage in aerobic exercise (AE) is to improve fitness, body composition and physical appearance. These parameters have an impact on bodily perception as conceptualized by the 'body image' (BI) construct. AE is known to have positive effects on pain perception, mood, and body image (BI). However, no study has hitherto investigated their interrelationship within one study. Methods: Participants were randomly assigned to an intervention group (IG, n = 16, 6 months of AE) or a passive control group (CG, n = 10). Frankfurt Body-Concept Scales (FKKS), Positive and Negative Affect Scale (PANAS), State and Trait Anxiety Inventory, warmth and heat pain thresholds (WPT, HPT), pain tolerance, and graded exercise test data from baseline (T0) and the end of the intervention (T6) were analyzed using a paired t-test (p < 0.05). Results: A significant increase in the BI dimension 'physical efficacy' was identified from T0 to T6, which correlated positively with PANAS Positive Affect Scale and HPT. Conclusion: Data in young adults undergoing AE indicate that changes in the BI sub-category 'physical efficacy' are closely linked with changes in positive affect and antinociception. These novel findings suggest that BI plays a role in antinociception and positive affect.

Does Social Exclusion Alter Sensory and Pain Thresholds in Children and Adolescents with Functional Abdominal Pain? - Results from a Preliminary Study

OBJECTIVE

Functional abdominal pain (AP) is a prevalent issue in childhood and adolescence. The contribution of psychosocial factors in the development and maintenance of this health problem is rather unclear, and experimental studies about underlying mechanisms are lacking. This study investigates whether experimentally induced social exclusion decreases sensory and pain thresholds in children suffering from AP.

SUBJECTS

Twenty children/adolescents with AP and 22 healthy controls.

METHODS

Children/adolescents participated in the Cyberball paradigm, which affects an experience of social exclusion. Thermal sensory and pain thresholds were measured before and after Cyberball.

RESULTS

Children/adolescents with AP showed a divergent reaction regarding their sensory threshold after social exclusion: The control group exhibited a tendency toward a decreased sensory threshold whereas the AP group remained stable. Concerning the pain threshold, no effect of social exclusion could be identified. The increase of both thresholds ("numbing") after Cyberball was positively correlated with symptoms of mental health issues.

CONCLUSIONS

This is the first study to investigate changes in sensory and pain thresholds following painful social interactions in a sample of children/adolescents with a chronic pain condition. Results suggest that AP and control children differ in their reaction of sensory thresholds, which might indicate an altered processing of social exclusion. Replication and further methodological improvements are needed.

The cornucopia of central disinhibition pain - An evaluation of past and novel concepts

Central disinhibition (CD), as applied to pain, decreases thresholds of endogenous systems. This provokes onset of spontaneous or evoked pain in an individual beyond the ability of the nervous system to inhibit pain resulting from a disease or tissue damage. The original CD concept as proposed by Craig entails a shift from the lateral pain pathway (i.e. discriminative pain processing) towards the medial pain pathway (i.e. emotional pain processing), within an otherwise neurophysiological intact environment. In this review, the original CD concept as proposed by Craig is extended by the primary "nociceptive pathway damage - CD" concept and the secondary "central pathway set point - CD". Thereby, the original concept may be transferred into anatomical and psychological non-functional conditions. We provide examples for either primary or secondary CD concepts within different clinical etiologies as well as present surrogate models, which directly mimic the underlying pathophysiology (A-fiber block) or modulate the CD pathway excitability (thermal grill). The thermal grill has especially shown promising advancements, which may be useful to examine CD pathway activation in the future. Therefore, within this topical review, a systematic review on the thermal grill illusion is intended to stimulate future research. Finally, the authors review different mechanism-based treatment approaches to combat CD pain.

Initial Evaluation of Pain Intensity Among Depressed Patients as a Possible Mediator Between Depression and Pain Complaints

Pain complaints are frequently described by depressed patients, and are mostly attributed to abnormal pain perception and modulation. The present study aimed to assess whether a unique pain processing profile differentiates depressed patients from healthy controls. Participants were 25 patients suffering from a moderate-severe unipolar depressive episode and 25 age and sex-matched healthy controls. Thermal stimuli were used to assess sensory threshold and pain threshold. Pain-60 temperature (temperature that induces pain ratings of 60 out of 100) was the first noxious stimuli to be administered during the experimental session. Central pain inhibition was assessed via conditioned pain modulation (CPM) and the degree of central nervous system excitability was assessed via mechanical temporal summation. Depressed patients reported higher levels of pain compared with healthy controls, and a significantly higher perceived pain during the last month. Additionally, they displayed significantly lower pain-60 temperature values compared with healthy controls (p = 0.01). Otherwise, no significant group differences were found in measures of pain perception and modulation. Our results suggest that the initial evaluation of pain intensity among depressed patients, as validated by pain-60 temperature values, is increased compared with healthy controls, and might be the mediator between depression and pain complaints. Possibly, depressed patients' negative bias in the processing of pain is similar to their processing pattern of facial expression or future events. Further studies are necessary in order to establish the mechanisms underlying the excessive pain complaints reported by patients with unipolar depression.

Pain Relief in Depressive Disorders: A Meta-Analysis of the Effects of Antidepressants

BACKGROUND

Pain is a common symptom in patients with depressive disorders, which, if present, worsens the prognosis. However, there is little empirical knowledge of the therapeutic effects of antidepressants on painful physical symptoms of patients with depressive disorders. Furthermore, tricyclic/tetracyclic antidepressants (TCAs) have not yet been included in existing meta-analyses.

METHODS

A broad, systematic search of PubMed literature on antidepressant drug treatment of patients with depressive disorders with comorbid pain symptoms was carried out. A random-effects meta-analysis has been performed among 3 different groups of drugs for the 2 end points: pain and depression.

RESULTS

Fourteen placebo-controlled studies with selective serotonin-noradrenaline reuptake inhibitors (SSNRIs) could be included, with 3 of them also investigating selective serotonin reuptake inhibitors (SSRIs). Three further placebo-controlled SSRI studies were identified, but only 2 placebo-controlled TCA studies.Both SSNRIs and SSRIs, but not TCAs, were significantly superior to placebo as regards their analgesic effects. However, all effects were small. For SSNRIs, there was a strong positive correlation between their effectiveness for pain relief and their positive effect on the mood of the patients.

DISCUSSION

The analgesic effects of SSNRIs and SSRIs in patients with primary depressive disorders can be interpreted as largely equivalent. Because of a lack of placebo-controlled TCA studies, the results for TCAs would be comparable only to those of SSRIs and SSNRIs, if non-placebo-controlled TCA studies were included. The positive correlation found indicates a close relationship of pain relief and antidepressant treatment effects. These results refer merely to patients with primary depressive disorders, not to patients with primary pain disorders. Further studies comparing the effects of different types of antidepressant drugs on pain in depressive patients are warranted.

Central Pain Processing in Early-Stage Parkinson's Disease: A Laser Pain fMRI Study

Background & Objective

Pain is a common non-motor symptom in Parkinson’s disease. As dopaminergic dysfunction is suggested to affect intrinsic nociceptive processing, this study was designed to characterize laser-induced pain processing in early-stage Parkinson’s disease patients in the dopaminergic OFF state, using a multimodal experimental approach at behavioral, autonomic, imaging levels.

Methods

13 right-handed early-stage Parkinson’s disease patients without cognitive or sensory impairment were investigated OFF medication, along with 13 age-matched healthy control subjects. Measurements included warmth perception thresholds, heat pain thresholds, and central pain processing with event-related functional magnetic resonance imaging (erfMRI) during laser-induced pain stimulation at lower (E = 440 mJ) and higher (E = 640 mJ) target energies. Additionally, electrodermal activity was characterized during delivery of 60 randomized pain stimuli ranging from 440 mJ to 640 mJ, along with evaluation of subjective pain ratings on a visual analogue scale.

Results

No significant differences in warmth perception thresholds, heat pain thresholds, electrodermal activity and subjective pain ratings were found between Parkinson’s disease patients and controls, and erfMRI revealed a generally comparable activation pattern induced by laser-pain stimuli in brain areas belonging to the central pain matrix. However, relatively reduced deactivation was found in Parkinson’s disease patients in posterior regions of the default mode network, notably the precuneus and the posterior cingulate cortex.

Conclusion

Our data during pain processing extend previous findings suggesting default mode network dysfunction in Parkinson’s disease. On the other hand, they argue against a genuine pain-specific processing abnormality in early-stage Parkinson’s disease. Future studies are now required using similar multimodal experimental designs to examine pain processing in more advanced stages of Parkinson’s disease.

Is Pain Perception Altered in People With Depression? A Systematic Review and Meta-Analysis of Experimental Pain Research

Although clinical studies suggest depressed patients may be more vulnerable to pain, experimental research is equivocal. This meta-analysis aimed to clarify whether depression is associated with altered pain perception in response to noxious stimulation and to identify factors that might influence this association. A search of major electronic databases was conducted to identify experimental studies investigating pain response in depressed participants versus healthy control participants using established pain outcome measures. Random effects meta-analysis of standardized mean differences was conducted on data from 32 studies (N = 1,317). For high-intensity noxious stimulation, overall pain tolerance was similar across depressed and control groups (Hedges g = .09, P = .71, studies = 10). For low-intensity stimulation, a small, but statistically significant higher mean sensory threshold (g = .35, P = .01, studies = 9) and pain threshold (g = .32, P = .02, studies = 25) was observed in depressed participants, suggesting diminished pain. However, considerable heterogeneity in the direction and magnitude of effects was observed, indicating a likely condition-specific effect of depression on pain. Subgroup analysis found that pain threshold/tolerance was increased in depression for exteroceptive (cutaneous) stimulation but decreased for interoceptive (ischemic) stimulation, but that substantial heterogeneity remained. Overall, results provide some support for altered pain processing in depression, but suggest this link is dependent upon modality and additional, unidentified factors.

PERSPECTIVE

This meta-analysis of experimental studies suggests potential effects of depression on pain perception are variable and likely to depend upon multiple factors. The contrasting pattern for ischemic versus other noxious stimuli suggests that stimulus modality is a key factor, which could help explain discrepancies across clinical and experimental findings.

Who is healthy? Aspects to consider when including healthy volunteers in QST--based studies-a consensus statement by the EUROPAIN and NEUROPAIN consortia

Clinical and human experimental pain studies often include so-called "healthy" controls in investigations of sensory abnormalities, using quantitative sensory testing (QST) as an outcome measure. However, the criteria for what is considered "healthy" vary among the different studies and between study centers and investigators, partly explaining the high variability of the results. Therefore, several aspects should be considered during inclusion of healthy volunteers in QST-based trials to have homogenous groups of healthy controls with less variability between human experimental studies, so that results are less likely to be false negative or false positive because of subject-related factors. The EUROPAIN and NEUROPAIN consortia aimed to define factors influencing the variability in selection of healthy subjects in QST-based studies before the start of both projects and to give recommendations how to minimize it based on the current literature and expertise of the participants. The present suggestions for inclusion criteria of healthy volunteers into QST-based trials describe a 2-level approach including standardized questionnaires enabling the collection of relevant information on sociodemographic data, medical history, current health status, coping strategies in dealing with pain, and the motivation of the volunteer to participate in the study. These suggestions are believed to help researchers interpret their results in comparison with others and improve the quality of clinical studies including healthy volunteers as controls or in human experimental pain studies. They aim to reduce any confounding factors. Furthermore, the acquired information will allow post hoc analyses of variance for different potential influencing factors.

Social Support Attenuates Physiological Stress Responses and Experimental Pain Sensitivity to Cold Pressor Pain

BACKGROUND

Social support improves health and has been shown to attenuate stress and pain. The precise characteristics of social support responsible for these effects, however, remain elusive.

PURPOSE

The purpose of this study is to examine the relative efficacy of social support versus a neutral non-verbal social presence to attenuate stress and pain.

METHODS

Seventy-six participants provided pain ratings and task assessments during a cold pressor task (CPT) in one of three conditions: verbal social support, neutral non-support, or alone. Reactivity to the CPT was assessed via cardiovascular measures, cortisol, and subjective ratings.

RESULTS

Participants receiving social support showed attenuated blood pressure, heart rate, and cortisol reactivity, as well as reduced pain ratings, task difficulty, tension, and effort compared to neutral non-support and alone conditions.

CONCLUSIONS

Social support, not the mere presence of another individual, attenuated stress and pain during a CPT. Given the negative health consequences of stress and pain, clinical studies incorporating social support into medical procedures and treatments are warranted.

Emotional modulation of pain and spinal nociception in persons with severe insomnia symptoms

BACKGROUND

Impaired sleep enhances pain, perhaps by disrupting pain modulation.

PURPOSE

Given that emotion modulates pain, the present study examined whether emotional modulation of pain and nociception is impaired in persons with severe insomnia symptoms relative to controls.

METHODS

Insomnia group (n = 12) met the International Classification of Diseases, tenth revision symptoms for primary insomnia and controls (n = 13) reported no sleep impairment. Participants were shown emotionally evocative pictures (mutilation, neutral, and erotica) during which suprathreshold pain stimuli were delivered to evoke pain and the nociceptive flexion reflex (NFR; physiological correlate of spinal nociception).

RESULTS

Emotional responses to pictures were similar in both groups, except that subjective valence/pleasure ratings were blunted in insomnia. Emotional modulation of pain and NFR was observed in controls, but only emotional modulation of NFR was observed in insomnia.

CONCLUSIONS

Consistent with previous findings, pain modulation is disrupted in insomnia, which might promote pain. This may stem from disrupted supraspinal circuits not disrupted brain-to-spinal cord circuits.

Further evidence of emotional allodynia in unmedicated young adults with major depressive disorder

BACKGROUND

Recent evidence suggests that sensitivity to the emotional sequela of experimental thermal pain(measured by emotional unpleasantness) is heightened in individuals with major depressive disorder(MDD), a phenomenon we termed "emotional allodynia". The aim of this study was to examine whether acute happy and sad mood induction alters emotional allodynia in MDD. We hypothesized that emotional allodynia will be a robust characteristic of individuals with MDD compared to healthy controls. Thus, it would remain following acute mood induction, independent of valence.

METHODS

Twenty-one subjects with current MDD and 21 well-matched healthy subjects(HC) received graded brief temperature stimuli following happy and sad mood inductions procedures(MIP). All subjects rated the intensity and affect(pleasantness/unpleasantness) of each stimulus. Sensory(pain intensity) and affective(pain unpleasantness) thresholds were determined by methods of constant stimuli.

RESULTS

The MIPs reliably induced happy and sad mood and the resulting induced mood and subjective arousal were not different between the groups at the time of temperature stimulation. Compared to HC, MDD individuals demonstrated emotional allodynia. We found significantly decreased affective pain thresholds whereby significantly lower temperatures became unpleasant in the MDD compared to the HC group. This was not observed for the sensory pain thresholds. Within the MDD, the affective pain thresholds were significantly lower than the corresponding pain intensity thresholds, whereby non-painful temperatures were already unpleasant for the MDD irrespective of the induced mood. This was not observed for the HC groups where the affective and pain intensity thresholds were comparable.

CONCLUSIONS

These findings suggest that emotional allodynia may be a chronic characteristic of current MDD. Future studies should determine if emotional allodynia persists after psychological or pharmacological interventions. Finally, longitudinal work should examine whether emotional allodynia is a result of or vulnerability for depression and the role it plays in the increased susceptibility for pain complaints in this disorder.

Brain-network mechanisms underlying the divergent effects of depression on spontaneous versus evoked pain in rats: a multiple single-unit study

Studies have reported divergent behavioral effects of depression on spontaneous vs. stimulus-evoked pain. However, the underlying neurobiological mechanisms are still unclear. The present study used a depression model of unpredictable chronic mild stress (UCMS) and pain models for spontaneous pain (i.e., the formalin test) and acute evoked pain (i.e., noxious thermal stimulation) in rats. The activity of neurons within thalamo-cortical circuits in the lateral and medial pain pathways was recorded by a multiple-channel recording technique, and behaviors were observed simultaneously. The results confirmed our previous findings that rats exposed to UCMS tended to exhibit decreased pain sensitivity to experimental stimuli but increased behavioral responses to ongoing pain. Based on the analysis of single-unit responses, the results demonstrated that the processing of spontaneous vs. evoked pain in a depressive-like state was altered in the opposite direction (activation vs. inhibition). The ensemble encoding analysis revealed that exposure to UCMS gave rise to enhanced inter-regional functional connectivity in spontaneous pain processing, but did not influence that of evoked pain. In addition, different brain activation patterns underlying the processing of spontaneous vs. evoked pain were observed. These findings revealed that the distinct response patterns of neurons within the pain-related brain circuits, especially in the affective pain pathway, mediate the divergent effects of depression on spontaneous vs. evoked pain. This is also the first report on the electrophysiology of depression models that provides direct evidence that the effect of depression on spontaneous and evoked pain may involve different brain mechanisms.

Comparison of blinding effectiveness between sham tDCS and placebo sertraline in a 6-week major depression randomized clinical trial

OBJECTIVE

To compare blinding integrity and associated factors for transcranial direct current stimulation (tDCS) vs. placebo-pill, the gold standard blinding method.

METHODS

Parallel trial. Depressed participants were randomized to verum/placebo sertraline and active/sham tDCS (2mA, 30-min 10-daily sessions and two additional, fortnight sessions) over 6weeks. Blinding was assessed in completers (n=102) and in a random subgroup (n=35) of raters and participants, in which we also inquired to qualitatively describe their strongest guessing reason.

RESULTS

Participants and raters presented similar performance for predicting treatment assignment at endpoint, correctly guessing tDCS and sertraline beyond chance. Nevertheless, clinical response was associated with correct prediction and tDCS non-responders failed to predict the allocation group. For tDCS, "trouble concentrating" was inversely associated with correct prediction. "Skin redness" was more reported for active-tDCS, but did not predict the allocation group. The qualitative reasons for raters' guessing were not associated with correct prediction, whereas for participants clinical response and adverse effects were directly and inversely associated with correct prediction, respectively.

CONCLUSION

Blinding integrity of tDCS and sertraline were comparable and mainly associated with efficacy rather than blinding failure.

SIGNIFICANCE

TDCS blinding can be improved by adopting parallel designs and avoiding subjects' awareness of skin redness.

Emotional modulation of pain and spinal nociception in persons with major depressive disorder (MDD)

Major depressive disorder (MDD) is associated with risk for chronic pain, but the mechanisms contributing to the MDD and pain relationship are unclear. To examine whether disrupted emotional modulation of pain might contribute, this study assessed emotional processing and emotional modulation of pain in healthy controls and unmedicated persons with MDD (14 MDD, 14 controls). Emotionally charged pictures (erotica, neutral, mutilation) were presented in 4 blocks. Two blocks assessed physiological-emotional reactions (pleasure/arousal ratings, corrugator electromyography (EMG), startle modulation, skin conductance) in the absence of pain and 2 blocks assessed emotional modulation of pain and the nociceptive flexion reflex (NFR, a physiological measure of spinal nociception) evoked by suprathreshold electric stimulations. Results indicated pictures generally evoked the intended emotional responses; erotic pictures elicited pleasure, subjective arousal, and smaller startle magnitudes, whereas mutilation pictures elicited displeasure, corrugator EMG activation, and subjective/physiological arousal. However, emotional processing was partially disrupted in MDD, as evidenced by a blunted pleasure response to erotica and a failure to modulate startle according to a valence linear trend. Furthermore, emotional modulation of pain was observed in controls but not MDD, even though there were no group differences in NFR threshold or emotional modulation of NFR. Together, these results suggest supraspinal processes associated with emotion processing and emotional modulation of pain may be disrupted in MDD, but brain to spinal cord processes that modulate spinal nociception are intact. Thus, emotional modulation of pain deficits may be a phenotypic marker for future pain risk in MDD.

The major brain endocannabinoid 2-AG controls neuropathic pain and mechanical hyperalgesia in patients with neuromyelitis optica

Recurrent myelitis is one of the predominant characteristics in patients with neuromyelitis optica (NMO). While paresis, visual loss, sensory deficits, and bladder dysfunction are well known symptoms in NMO patients, pain has been recognized only recently as another key symptom of the disease. Although spinal cord inflammation is a defining aspect of neuromyelitis, there is an almost complete lack of data on altered somatosensory function, including pain. Therefore, eleven consecutive patients with NMO were investigated regarding the presence and clinical characteristics of pain. All patients were examined clinically as well as by Quantitative Sensory Testing (QST) following the protocol of the German Research Network on Neuropathic Pain (DFNS). Additionally, plasma endocannabinoid levels and signs of chronic stress and depression were determined. Almost all patients (10/11) suffered from NMO-associated neuropathic pain for the last three months, and 8 out of 11 patients indicated relevant pain at the time of examination. Symptoms of neuropathic pain were reported in the vast majority of patients with NMO. Psychological testing revealed signs of marked depression. Compared to age and gender-matched healthy controls, QST revealed pronounced mechanical and thermal sensory loss, strongly correlated to ongoing pain suggesting the presence of deafferentation-induced neuropathic pain. Thermal hyperalgesia correlated to MRI-verified signs of spinal cord lesion. Heat hyperalgesia was highly correlated to the time since last relapse of NMO. Patients with NMO exhibited significant mechanical and thermal dysesthesia, namely dynamic mechanical allodynia and paradoxical heat sensation. Moreover, they presented frequently with either abnormal mechanical hypoalgesia or hyperalgesia, which depended significantly on plasma levels of the endogenous cannabinoid 2-arachidonoylglycerole (2-AG). These data emphasize the high prevalence of neuropathic pain and hyperalgesia in patients with NMO. The degree of mechanical hyperalgesia reflecting central sensitization of nociceptive pathways seems to be controlled by the major brain endocannabinoid 2-AG.

Insular dysfunction and descending pain inhibition in anorexia nervosa

OBJECTIVE

Reduced perception of pain is a well-established phenomenon in patients with anorexia nervosa (AN). We tested the hypothesis that altered processing of pain within the insula might account for reduced perception of pain.

METHOD

Heat pain thresholds were obtained in nineteen patients with AN and matched controls. Thereafter, a thermode was used to deliver thermal painful stimuli to the right arm during functional magnetic resonance imaging (fMRI) measurements. Stimuli were initiated for 10 s from a baseline resting temperature (32°C) to three different levels (37, 42, 45°C).

RESULTS

Significantly increased heat pain thresholds were observed in patients. A stronger activation during heat pain perception was found in the left posterior insula in controls. In contrast, higher levels of activity were shown in the ipsilateral pons in patients when compared to controls. In patients, we found a significant interrelation between the depression score (Beck depression inventory) and heat pain activations.

CONCLUSION

We suggest that reduced activity in the left posterior insula might contribute to increased pain thresholds in patients, while increased activations in the right anterior insula and pons mirror augmented sympathetic modulation putatively related to amplification of adrenergic descending pain inhibition. In addition, pain thresholds and brain activations were influenced by disease-inherent depressed mood.

Thresholds and perception of cold pain, heat pain, and the thermal grill illusion in patients with major depressive disorder

OBJECTIVE

The thermal grill illusion (TGI) in which interlacing cold and warm bars create the illusion of a painful sensation has been suggested as an experimental model for central pain states and pain processing. The aim of this study was to use this technique to gain further insights into the altered pain perception in major depressive disorder (MDD).

METHODS

In 18 unmedicated patients with MDD, cold and heat pain thresholds (CPT/HPT) as well as the perception of the TGI were examined and compared with 18 matched controls.

RESULTS

CPT and HPT were significantly increased in patients (7.9°C and 47.5°C) compared with controls (15.9°C and 45.2°C, respectively; p < .05). In the range of TGI stimuli that were perceived painful by controls, the patients did not indicate painful sensations, thereby indicating a shift of the stimulus-response curve of TGI pain perception toward higher stimulus intensities, that is, greater temperature differentials between cold and warm bars (11.5°C for controls, 16.7°C for patients). The patients rated the pain intensity perceived at the respective pain thresholds (CPT and HPT) in tendency higher than did the controls, whereas they perceived the TGI less painful despite increased stimulus intensities. Unpleasantness ratings were similar between groups.

CONCLUSIONS

CPT, HPT and temperature differentials for the perception of the TGI, were increased in patients with MDD as compared with controls. Pain intensity, however, was rated differently for CPT and HPT, where patients indicated higher ratings in tendency, and for the TGI stimulation, where pain was perceived less intense.

The influence of physical activity on pain thresholds in patients with depression and multiple somatoform symptoms

OBJECTIVES

Pain is a common symptom with high occurrence in somatoform syndromes and depressive disorders. Research in this area often focuses on experimental induction of pain and subsequent assessment of pain thresholds, ensuring repeatable stimuli of defined quality. Results on sensitivity to experimental pain in major depression are inconclusive, and data on pain thresholds in multiple somatoform symptoms are scarce. The goals of the present study were to differentiate between groups regarding the pressure pain thresholds, and to investigate the possible influence of physical activity on the pain thresholds in these groups. We postulate that physical fitness and physical activity influence pain thresholds in depression and persons with multiple somatoform symptoms.

METHODS

Thirty-eight persons with major depression, 26 persons with a minimum of 6 to 8 somatoform symptoms (somatoform symptom index 8, SSI-8), and 47 healthy participants participated in the study. Baseline values of pressure pain thresholds assessed at different sites of the body were compared with those after 1 week of increased and 1 week of reduced physical activity.

RESULTS

We used repeated measurement design (MANCOVA) and partial correlations for data analysis. Depressed participants reported lower pain thresholds compared with controls, and persons with SSI-8 showed intermediate thresholds. After 1 week of physical activity, participants reported higher pain thresholds. Men had higher pain thresholds following activity as compared with women. Participants who reported higher general fitness also showed higher pain thresholds. Sensitivity to pressure pain is associated with depression, but not with multiple somatoform symptoms.

DISCUSSION

Short low-graded exercise can have reducing effects on perception of pressure pain. Physical activity level is a relevant covariate when using pressure pain assessment. Reduced general fitness can partially account for lower pain thresholds in depression.

Cerebral serotonin transporter asymmetry in females, males and male-to-female transsexuals measured by PET in vivo

The serotonergic system modulates brain functions that are considered to underlie affective states, emotion and cognition. Several lines of evidence point towards a strong lateralization of these mental processes, which indicates similar asymmetries in associated neurotransmitter systems. Here, our aim was to investigate a potential asymmetry of the serotonin transporter distribution using positron emission tomography and the radioligand [(11)C]DASB in vivo. As brain asymmetries may differ between sexes, we further aimed to compare serotonin transporter asymmetry between females, males and male-to-female (MtF) transsexuals whose brains are considered to be partly feminized. Voxel-wise analysis of serotonin transporter binding in all groups showed both strong left and rightward asymmetries in several cortical and subcortical structures including temporal and frontal cortices, anterior cingulate, hippocampus, caudate and thalamus. Further, male controls showed a rightward asymmetry in the midcingulate cortex, which was absent in females and MtF transsexuals. The present data support the notion of a lateralized serotonergic system, which is in line with previous findings of asymmetric serotonin-1A receptor distributions, extracellular serotonin concentrations, serotonin turnover and uptake. The absence of serotonin transporter asymmetry in the midcingulate in MtF transsexuals may be attributed to an absence of brain masculinization in this region.

[The processing of pain in psychiatric diseases]

The perception and processing of pain is disturbed in many psychiatric diseases. Some diseases are known to show decreased perception of pain (e.g. borderline personality disorder), while others are associated with augmented pain perception (e.g. alcohol and drug dependence). The close relationship between psychiatric diseases and pain is most probably caused by aberrant processing of pain in brain structures, known to be involved in psychiatric disorders as well. Aberrant perception and processing of pain in patients with anorexia nervosa (AN) will be used to demonstrate this close relationship. Dysfunction within the insula has been suggested to account for many features of AN and might contribute to reduced pain perception. Moreover, it might lead to increased adrenergic descending inhibition associated with increased sympathetic modulation. Thus, pain research might be able to alter our view on autonomic regulation, which is putatively associated with increased cardiac mortality of the disease.

An fMRI study on the acute effects of exercise on pain processing in trained athletes

Endurance exercise is known to promote sustained antinociceptive effects, and there is evidence that the reduction of pain perception mediated by exercise is driven by central opioidergic neurotransmission. To directly investigate the involved brain areas and the underlying neural mechanisms in humans, thermal heat-pain challenges were applied to 20 athletes during 4 separate functional magnetic resonance imaging (fMRI) scans, i.e., before and after 2 hours of running (exercise condition) and walking (control condition), respectively. Imaging revealed a reproducible pattern of distributed pain-related activation in all 4 conditions, including the mesial and lateral pain systems, and the periaqueductal gray (PAG) as a key region of the descending antinociceptive pathway. At the behavioral level, running as compared with walking decreased affective pain ratings. The influence of exercise on pain-related activation was reflected in a significant time × treatment interaction in the PAG, along with similar trends in the pregenual anterior cingulate cortex and the middle insular cortex, where pain-induced activation levels were elevated after walking, but decreased or unchanged after running. Our findings indicate that enhanced reactive recruitment of endogenous antinociceptive mechanisms after aversive repeated pain exposure is attenuated by exercise. The fact that running, but not walking, reproducibly elevated β-endorphin levels in plasma indicates involvement of the opioidergic system in exercise. This may argue for an elevated opioidergic tone in the brain of athletes, mediating antinociceptive mechanisms. Our findings provide the first evidence using functional imaging to support the role of endurance exercise in pain modulation.

The effects of sex and gender role on responses to pressure pain

Background: Several studies on experimental mechanical pain suggested a strong influence of sex demonstrating females to be more sensitive. We examined the hypothesis that not only sex but also gender role affects pain responsiveness and looked for mediators of this effect.

Method: As indicators of pain the threshold the intensity and the unpleasantness of pressure stimuli were measured, as well as sensory and affective quality of pain. The gender role of 74 students was assessed by the Bem Sex Role Inventory (BSRI). Furthermore several psychological variables assumed to be potential mediators (catastrophising, fear of pain, depressive symptoms, pain coping) were obtained.

Results: ANOVA revealed significant main effects of sex in all pain variables except affective quality of pain. Contrary to our hypothesis gender role had no influence on pain responses, neither was there an interaction of sex and gender. Fear of pain just missed the significance level identifying it as mediator of the sex effect on affective pain.

Conclusions: In summary, our study corroborated previous findings that women are more responsive to mechanical pain stimuli with effect sizes being medium to large, whereas gender role did not predict any of the assessed pain parameters. No convincing evidence was found that the influence of sex is predominantly mediated by psychological characteristics of the individual.

Perception for ischemic pain shows similarities in adjustment disorder and major depression

We recently described an increase of pain thresholds and tolerances for thermal and electrical pain in patients suffering from adjustment disorder (AD). Furthermore, we presented evidence that pain perception in major depressive disorder (MDD) depends on pain modality, with thresholds for ischemic pain being decreased compared to increased thermal and electrical pain thresholds. Here, we investigated perception of experimentally induced ischemic pain in 15 patients suffering from AD (subtype with depressive symptoms) and controls matched for age and sex in order to examine whether a similar pattern of modality dependent pain perception can be established. Thresholds and tolerances were assessed on both sides of the body. We found a significant decrease of ischemic pain thresholds in AD patients as compared to controls. Analogue findings have been reported for pain perception in MDD, therefore suggesting similarities with regards to pain perception in both disorders. This adds weight to the assumption that depressive symptomatology might alter pain sensitivity in this subtype of AD since symptoms are milder, yet comparable to MDD.

Depression, cytokines and experimental pain: evidence for sex-related association patterns

BACKGROUND

There is robust evidence that altered neural-immune interactions including increased levels of proinflammatory cytokines are involved in both the pathogenesis of depression and altered pain processing. Proinflammatory cytokines induce sickness behavior, a constellation of symptoms that bears a strong similarity to those of depression. A feature of sickness behavior is enhanced pain sensitivity and it has been suggested that proinflammatory cytokines interact with pain processing directly and via several neurobiological pathways. Previous research indicates that depression and pain are closely related. We investigated the association between proinflammatory cytokines and experimental pain in major depression.

METHODS

Psychopathological variables, pressure pain thresholds (PPT) and concentrations of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) were measured in 37 outpatients with major depression and 48 healthy controls.

RESULTS

Compared with controls, depressed patients exhibited significantly higher levels of TNF-α and significantly decreased PPT indicating enhanced pain sensitivity. The group differences were robust when adjusting for sex and body mass index, although sex was significantly related to PPT. No group difference was observed in IL-6. PPT correlated significantly with TNF-α in women but not in men.

LIMITATIONS

Because of the cross-sectional design, causality of the relation between TNF-α and pain cannot be determined. Results should be considered preliminary given the small sample size.

CONCLUSION

The present findings suggest that increased pain sensitivity in depression may be linked to increased TNF-α concentration. The absence of this association in men is discussed in terms of pain-related psychobiological sex differences.

Pain, sensory function, and neurogenic inflammatory response in young women with low mood

OBJECTIVE

To determine the relationship of mood status to pain complaints, sensory function, neurogenic inflammatory response, and general health in young women.

METHODS

Ninety-three women aged 18-29 participated in the study and were categorized by SCL-90-R depression score into low-mood (n=21) and normal-mood (n=72) groups. All subjects were below the threshold for possible clinical depression.

RESULTS

Low mood was associated with decreased tactile sensitivity, reduced response to topical capsaicin, and increased complaints of back, joint, muscle, and visceral pain, but not headache, when compared to normal mood controls. Low mood was also associated with reported poorer health and physical functioning, increased psychopathology, and family history of mood problems.

CONCLUSION

These data show that even subclinical low mood is associated with marked alterations in health and psychophysiological function.

Pseudohypoalgesia on the skin: a novel view on the paradox of pain perception in depression

Previous studies reported increased heat pain thresholds and decreased ischemic pain thresholds in patients experiencing depression. The increased sensitivity to ischemic muscle pain was assumed to represent a model for the investigation of physical symptoms in the disease. Here, we explored how the serotonin and noradrenaline reuptake inhibitor duloxetine influences experimental pain thresholds and tolerances in depressed patients during treatment. Twenty-two patients experiencing unipolar depression were included. Pain assessments were conducted unmedicated at baseline, after 1 week, and after 6 weeks of duloxetine treatment. We observed the expected clinical response of patients indicated by a significant reduction in the Montgomery Depression Rating Scale after 6 weeks. At baseline, we found increased heat pain thresholds in patients in comparison to controls while patients simultaneously rated augmented pain perception on the visual analog scale. In contrast, patients were significantly more perceptive to ischemic muscle pain at baseline. During treatment, the examined pain thresholds showed differential changes: Increased heat pain thresholds of patients normalized during treatment, whereas no significant change was observed for ischemic pain thresholds. Thus, our results might change the view on the paradox of pain perception in major depression because increased heat pain thresholds are associated with augmented pain perception in the disease.

Sad mood increases pain sensitivity upon thermal grill illusion stimulation: implications for central pain processing

In different fields of neuroscience research, illusions have successfully been used to unravel underlying mechanisms of stimulus processing. One such illusion existing for the field of pain research is the so-called thermal grill illusion. Here, painful sensations are elicited by interlacing warm and cold bars, with stimulus intensities (temperatures) of these bars being below the respective heat pain or cold pain thresholds. To date, the underlying mechanisms of this phenomenon are not completely understood. There is some agreement, however, that the sensation evoked by this stimulation is generated by central nervous interactions. Therefore, we followed two approaches in this study: firstly, we aimed at developing and validating a water-driven device which might be used in fMRI scanners in future studies - subject to minor adaptations. Secondly, we aimed to interfere with this illusion by induction of a sad mood state, a procedure which is suggested to influence central nervous structures that are also involved in pain processing. The newly developed device induced thermal grill sensations similar to those reported in the literature. Induction of sad, but not neutral mood states, resulted in higher pain and unpleasantness ratings of the painful illusion. These findings might be of importance for the understanding of pain processing in healthy volunteers, but putatively even more so in patients with major depressive disorder. Moreover, our results might indicate that central nervous structures involved in the affective domain or cognitive domain of pain processing might be involved in the perception of the illusion.

Effects of duloxetine treatment on brain response to painful stimulation in major depressive disorder

Major depressive disorder (MDD) is characterized by a constellation of affective, cognitive, and somatic symptoms associated with functional abnormalities in relevant brain systems. Painful stimuli are primarily stressful and can trigger consistent responses in brain regions highly overlapping with the regions altered in MDD patients. Duloxetine has proven to be effective in treating both core emotional symptoms and somatic complaints in depression. This study aimed to assess the effects of duloxetine treatment on brain response to painful stimulation in MDD patients. A total of 13 patients and a reference group of 20 healthy subjects were assessed on three occasions (baseline, treatment week 1, and week 8) with functional magnetic resonance imaging (fMRI) during local application of painful heat stimulation. Treatment with duloxetine was associated with a significant reduction in brain responses to painful stimulation in MDD patients in regions generally showing abnormally enhanced activation at baseline. Clinical improvement was associated with pain-related activation reductions in the pregenual anterior cingulate cortex, right prefrontal cortex, and pons. Pontine changes were specifically related to clinical remission. Increased baseline activations in the right prefrontal cortex and reduced deactivations in the subgenual anterior cingulate cortex predicted treatment responders at week 8. This is the first fMRI study addressed to assess the effect of duloxetine in MDD. As a novel approach, the application of painful stimulation as a basic neural stressor proved to be effective in mapping brain response changes associated with antidepressant treatment and brain correlates of symptom improvement in regions of special relevance to MDD pathophysiology.

Increased thermal and mechanical nociceptive thresholds in rats with depressive-like behaviors

Clinical observations suggest that depressed patients were less sensitive to experimental pain than healthy subjects. However, few animal studies are reported concerning the association of depression and pain. The purpose of this study was to investigate the effects of unpredictable chronic mild stress (UCMS) induced depression on the perceived intensity of painful stimulation in rats. We measured the thermal and mechanical paw withdrawal thresholds (PWT) of normal and spinal nerve ligated (SNL) rats using hot plate test and von Frey test, respectively. The results showed that rats exposed to UCMS exhibited significantly higher thermal and mechanical pain thresholds in comparison to the non-depressed controls. In particular, the PWT of the SNL group was restored to nearly normal level after three weeks of UCMS, and even comparable to that of the control group. These results strongly suggest that the depressed subjects have decreased sensitivity to externally applied noxious stimulation, which is consistent with our previous findings.

Histories of major depression and premenstrual dysphoric disorder: Evidence for phenotypic differences

This study examined unique versus shared stress and pain-related phenotypes associated with premenstrual dysphoric disorder (PMDD) and prior major depressive disorder (MDD). Sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal (HPA)-axis measures were assessed at rest and during mental stress, as well as sensitivity to cold pressor and tourniquet ischemic pain tasks in four groups of women: (1) non-PMDD with no prior MDD (N=18); (2) non-PMDD with prior MDD (N=9); (3) PMDD with no prior MDD (N=17); (4) PMDD with prior MDD (N=10). PMDD women showed blunted SNS responses to stress compared to non-PMDD women, irrespective of prior MDD; while women with prior MDD showed exaggerated diastolic blood pressure responses to stress versus never depressed women, irrespective of PMDD. However, only in women with histories of MDD did PMDD women have lower cortisol concentrations than non-PMDD women, and only in non-PMDD women was MDD associated with reduced cold pressor pain sensitivity. These results suggest both unique phenotypic differences between women with PMDD and those with a history of MDD, but also indicate that histories of MDD may have special relevance for PMDD.