Enhanced pain expectation in migraine: EEG-based evidence for impaired prefrontal function

Novel neurophysiological evidence for preserved pain habituation across chronic pain conditions

OBJECTIVE

The present study aimed to investigate whether subjective and objective measures of pain habituation can be used as potential markers for central sensitization across various chronic pain patients.

METHODS

Two blocks of contact-heat stimuli were applied to a non-painful area in 93 chronic pain patients (low back pain, neuropathic pain, and complex regional pain syndrome) and 60 healthy controls (HC). Habituation of pain ratings, contact-heat evoked potentials (CHEP), and sympathetic skin responses (SSR) was measured.

RESULTS

There was no significant difference in any measure of pain habituation between patients and HC. Even patients with apparent clinical signs of central sensitization showed no reduced pain habituation. However, prolonged baseline CHEP and SSR latencies (stimulation block 1) were found in patients compared to HC (CHEP: Δ-latency = 23 ms, p = 0.012; SSR: Δ-latency = 100 ms, p = 0.022).

CONCLUSION

Given the performed multimodal neurophysiological testing protocol, we provide evidence indicating that pain habituation may be preserved in patients with chronic pain and thereby be of limited use as a sensitive marker for central sensitization. These results are discussed within the framework of the complex interactions between pro- and antinociceptive mechanism as well as methodological issues. The prolonged latencies of CHEP and SSR after stimulation in non-painful areas may indicate subclinical changes in the integrity of thermo-nociceptive afferents, or a shift towards antinociceptive activity. This shift could potentially affect the relay of ascending signals.

SIGNIFICANCE

Our findings challenge the prevailing views in the literature and may encourage further investigations into the peripheral and central components of pain habituation, using advanced multimodal neurophysiological techniques.

The Role of the Mu Opioid Receptors of the Medial Prefrontal Cortex in the Modulation of Analgesia Induced by Acute Restraint Stress in Male Mice

Mu opioid receptors (MORs) represent a vital mechanism related to the modulation of stress-induced analgesia (SIA). Previous studies have reported on the gamma-aminobutyric acid (GABA)ergic "disinhibition" mechanisms of MORs on the descending pain modulatory pathway of SIA induced in the midbrain. However, the role of the MORs expressed in the medial prefrontal cortex (mPFC), one of the main cortical areas participating in pain modulation, in SIA remains completely unknown. In this study, we investigated the contributions of MORs expressed on glutamatergic (MORGlut) and GABAergic (MORGABA) neurons of the medial prefrontal cortex (mPFC), as well as the functional role and activity of neurons projecting from the mPFC to the periaqueductal gray (PAG) region, in male mice. We achieved this through a combination of hot-plate tests, c-fos staining, and 1 h acute restraint stress exposure tests. The results showed that our acute restraint stress protocol produced mPFC MOR-dependent SIA effects. In particular, MORGABA was found to play a major role in modulating the effects of SIA, whereas MORGlut seemed to be unconnected to the process. We also found that mPFC-PAG projections were efficiently activated and played key roles in the effects of SIA, and their activation was mediated by MORGABA to a large extent. These results indicated that the activation of mPFC MORGABA due to restraint stress was able to activate mPFC-PAG projections in a potential "disinhibition" pathway that produced analgesic effects. These findings provide a potential theoretical basis for pain treatment or drug screening targeting the mPFC.

Perturbation walking effects on prefrontal cortical activation and walking performance in older women with and without osteoarthritis: a FNIRS study

Introduction

Perturbation walking (PW) has been shown to improve gait, however its effect on the cortical control of gait might provide insights on neural mechanisms underlying falls in adults with osteoarthritis. The objective of this study is to investigate the effect of PW on prefrontal cortical (PFC) activation in older women with (OA) and without osteoarthritis (HOA). We hypothesized that there would be an increase in PFC activation during PW relative to comfortable walking (CW) and higher increase in PFC activation during PW in HOA compared to OA.

Methods

Twenty community-dwelling older women (66.7 ± 5.41 years old) walked on an instrumented treadmill that provided perturbations at pseudo-random intervals between 5-25 s using a counterbalanced design. Functional Near Infrared Spectroscopy was used to quantify PFC oxygenated hemoglobin (HbO2) and deoxyhemoglobin (Hb) levels, while standing prior to the task as a baseline. A linear mixed effects model was conducted to investigate the effects of cohort (HOA vs OA), task (PW vs CW), and their interaction on HbO2 (μM) and Hb (μM) levels.

Results

HbO2 and Hb levels differed significantly between CW and PW tasks for both cohorts (P < 0.001) and demonstrated significant task by cohort interaction (P < 0.05). In addition, we found changes in walking performance (stride time, stride length, stride width and stance time) during and after PW. Spearman correlation demonstrated a strong association between increased stance time, increased body mass index and decreased PFC activation during PW. No other significant results were found.

Discussion

This study found increase in PFC activation during PW and gait adaptation after a short bout of PW in HOA and OA. This increase in PFC activation was higher in HOA compared to OA, particularly during PW tasks, and was consistent with theory of limitations in mobility affecting neural activation in older adults. Further work remains to examine how pain, obesity, and mobility impacts cortical control in older adults with and without osteoarthritis.

The effect of unpredictability on the perception of pain: a systematic review and meta-analysis

ABSTRACT

Despite being widely assumed, the worsening impact of unpredictability on pain perception remains unclear because of conflicting empirical evidence, and a lack of systematic integration of past research findings. To fill this gap, we conducted a systematic review and meta-analysis focusing on the effect of unpredictability on pain perception. We also conducted meta-regression analyses to examine the moderating effect of several moderators associated with pain and unpredictability: stimulus duration, calibrated stimulus pain intensity, pain intensity expectation, controllability, anticipation delay, state and trait negative affectivity, sex/gender and age of the participants, type of unpredictability (intensity, onset, duration, location), and method of pain induction (thermal, electrical, mechanical pressure, mechanical distention). We included 73 experimental studies with adult volunteers manipulating the (un)predictability of painful stimuli and measuring perceived pain intensity and pain unpleasantness in predictable and unpredictable contexts. Because there are insufficient studies with patients, we focused on healthy volunteers. Our results did not reveal any effect of unpredictability on pain perception. However, several significant moderators were found, ie, targeted stimulus pain intensity, expected pain intensity, and state negative affectivity. Trait negative affectivity and uncontrollability showed no significant effect, presumably because of the low number of included studies. Thus, further investigation is necessary to clearly determine their role in unpredictable pain perception.

Unveiling the Role of Contingent Negative Variation (CNV) in Migraine: A Review of Electrophysiological Studies in Adults and Children

Migraine has been considered a chronic neuronal-based pain disorder characterized by the presence of cortical hyperexcitability. The Contingent Negative Variation (CNV) is the most explored electrophysiological index in migraine. However, the findings show inconsistencies regarding its functional significance. To address this, we conducted a review in both adults and children with migraine without aura to gain a deeper understanding of it and to derive clinical implications. The literature search was conducted in the PubMed, SCOPUS and PsycINFO databases until September 2022m and 34 articles were retrieved and considered relevant for further analysis. The main results in adults showed higher CNV amplitudes (with no habituation) in migraine patients. Electrophysiological abnormalities, particularly focused on the early CNV subcomponent (eCNV), were especially prominent a few days before the onset of a migraine attack, normalizing during and after the attack. We also explored various modulatory factors, including pharmacological treatments-CNV amplitude was lower after the intake of drugs targeting neural hyperexcitability-and other factors such as psychological, hormonal or genetic/familial influences on CNV. Although similar patterns were found in children, the evidence is particularly scarce and less consistent, likely due to the brain's maturation process during childhood. As the first review exploring the relationship between CNV and migraine, this study supports the role of the CNV as a potential neural marker for migraine pathophysiology and the prediction of pain attacks. The importance of further exploring the relationship between this neurophysiological index and childhood migraine is critical for identifying potential therapeutic targets for managing migraine symptoms during its development.

Repeated exposure to aversive sensations differentially affects neural gating and bodily perception

Habituation to bodily sensations is highly relevant for the experience of chronic bodily symptoms, but the neural mechanisms behind diminished habituation are currently unclear. One potentially relevant mechanism is neural gating (NG), reflected as the short-term suppression of cortical responses to redundant stimuli. We investigated the effects of repeated exposure to aversive sensations on NG and subjective perception in 91 healthy adults, by measuring their NG of respiratory and electrocutaneous stimuli using electroencephalography during two sessions separated by one week, in addition to their self-report of intensity and unpleasantness of the sensations. To test for intra- and cross-modal effects, 1/2 participants returned three times in the intervening week to experience additional aversive respiratory stimulation, while the other 1/2 received aversive electrocutaneous stimulation. Participants reported lower unpleasantness of all sensations in the final session (intra- and cross-modal habituation). NG was improved for respiratory sensations only in the group receiving additional respiratory stimulation (intra-modal habituation). We found no relationships between NG and perceptual habituation, adding to the mixed results on the relevance of NG to perceptual changes in healthy adults. Future research with clinical populations and different methods is encouraged to further clarify the mechanisms behind neural gating and diminished symptom habituation.

Habituation to Pain in Patients with Chronic Pain: Clinical Implications and Future Directions

In this review, the latest insights into habituation to pain in chronic pain are summarized. Using a systematic search, results of studies on the evidence of habituation to (experimental) pain in migraine, chronic low back pain, fibromyalgia, and a variety of chronic pain indications are presented. In migraine, reduced habituation based on self-report and the EEG-based N1 and N2-P2 amplitude is reported, but the presence of contradictory results demands further replication in larger, well-designed studies. Habituation to pain in chronic low back pain seems not to differ from controls, with the exception of EEG measures. In fibromyalgia patients, there is some evidence for reduced habituation of the N2-P2 amplitude. Our analysis shows that the variability between outcomes of studies on habituation to pain is high. As the mechanisms underlying habituation to pain are still not fully understood and likely involve several pathways, it is now too early to conclude that habituation to pain is related to clinical outcomes and can be used as a diagnostic marker. The review ends with a discussion on future directions for research including the use of standard outcome measures to improve comparisons of habituation to pain in patients and controls, as well as a focus on individual differences.

TMS-evoked EEG potentials demonstrate altered cortical excitability in migraine with aura

Migraine is associated with altered sensory processing, that may be evident as changes in cortical responsivity due to altered excitability, especially in migraine with aura. Cortical excitability can be directly assessed by combining transcranial magnetic stimulation with electroencephalography (TMS-EEG). We measured TMS evoked potential (TEP) amplitude and response consistency as these measures have been linked to cortical excitability but were not yet reported in migraine.We recorded 64-channel EEG during single-pulse TMS on the vertex interictally in 10 people with migraine with aura and 10 healthy controls matched for age, sex and resting motor threshold. On average 160 pulses around resting motor threshold were delivered through a circular coil in clockwise and counterclockwise direction. Trial-averaged TEP responses, frequency spectra and phase clustering (over the entire scalp as well as in frontal, central and occipital midline electrode clusters) were compared between groups, including comparison to sham-stimulation evoked responses.Migraine and control groups had a similar distribution of TEP waveforms over the scalp. In migraine with aura, TEP responses showed reduced amplitude around the frontal and occipital N100 peaks. For the migraine and control groups, responses over the scalp were affected by current direction for the primary motor cortex, somatosensory cortex and sensory association areas, but not for frontal, central or occipital midline clusters.This study provides evidence of altered TEP responses in-between attacks in migraine with aura. Decreased TEP responses around the N100 peak may be indicative of reduced cortical GABA-mediated inhibition and expand observations on enhanced cortical excitability from earlier migraine studies using more indirect measurements.

Application of EEG in migraine

Migraine is a common disease of the nervous system that seriously affects the quality of life of patients and constitutes a growing global health crisis. However, many limitations and challenges exist in migraine research, including the unclear etiology and the lack of specific biomarkers for diagnosis and treatment. Electroencephalography (EEG) is a neurophysiological technique for measuring brain activity. With the updating of data processing and analysis methods in recent years, EEG offers the possibility to explore altered brain functional patterns and brain network characteristics of migraines in depth. In this paper, we provide an overview of the methodology that can be applied to EEG data processing and analysis and a narrative review of EEG-based migraine-related research. To better understand the neural changes of migraine or to provide a new idea for the clinical diagnosis and treatment of migraine in the future, we discussed the study of EEG and evoked potential in migraine, compared the relevant research methods, and put forwards suggestions for future migraine EEG studies.

Clinical use of Electroencephalography in the Assessment of Acute Thermal Pain: A Narrative Review Based on Articles From 2009 to 2019

Nowadays, no practical system has successfully been able to decode and predict pain in clinical settings. The inability of some patients to verbally express their pain creates the need for a tool that could objectively assess pain in these individuals. Neuroimaging techniques combined with machine learning are seen as possible candidates for the identification of pain biomarkers. This review aimed to address the potential use of electroencephalographic features as predictors of acute experimental pain. Twenty-six studies using only thermal stimulations were identified using a PubMed and Scopus search. Combinations of the following terms were used: "EEG," "Electroencephalography," "Acute," "Pain," "Tonic," "Noxious," "Thermal," "Stimulation," "Brain," "Activity," "Cold," "Subjective," and "Perception." Results revealed that contact-heat-evoked potentials have been widely recorded over central areas during noxious heat stimulations. Furthermore, a decrease in alpha power over central regions was revealed, as well as increased theta and gamma powers over frontal areas. Gamma and theta rhythms were associated with connectivity between sensory and affective regions involved in pain processing. A machine learning analysis revealed that the gamma band is a predominant predictor of acute thermal pain. This review also addressed the need of supplementing current spectral features with techniques that allow the investigation of network dynamics.

Inter-individual differences in pain anticipation and pain perception in migraine: Neural correlates of migraine frequency and cortisol-to-dehydroepiandrosterone sulfate (DHEA-S) ratio

Previous studies targeting inter-individual differences in pain processing in migraine mainly focused on the perception of pain. Our main aim was to disentangle pain anticipation and perception using a classical fear conditioning task, and investigate how migraine frequency and pre-scan cortisol-to-dehydroepiandrosterone sulfate (DHEA-S) ratio as an index of neurobiological stress response would relate to neural activation in these two phases. Functional Magnetic Resonance Imaging (fMRI) data of 23 participants (18 females; mean age: 27.61± 5.36) with episodic migraine without aura were analysed. We found that migraine frequency was significantly associated with pain anticipation in brain regions comprising the midcingulate and caudate, whereas pre-scan cortisol-to DHEA-S ratio was related to pain perception in the pre-supplementary motor area (pre-SMA). Both results suggest exaggerated preparatory responses to pain or more general to stressors, which may contribute to the allostatic load caused by stressors and migraine attacks on the brain.

Psychological factors associated with headache frequency, intensity, and headache-related disability in migraine patients

Background

Several psychological cofactors of migraine have been identified, but relationships to different headache parameters (e.g., headache frequency vs. headache-related disability) are only incompletely understood.

Methods

We cross-sectionally assessed 279 migraine patients at their first presentation at our tertiary headache center. We obtained headache and acute medication frequency, pain intensity, the Migraine Disability Assessment Scale (MIDAS), and the Pain Disability Index (PDI) as headache-related outcomes as well as scores of the Hospital Anxiety and Depression Scale (HADS), the Pain Catastrophizing Scale (PCS), Pain-Related Control Scale (PRCS), and Avoidance Endurance Questionnaire (AEQ) as psychological factors.

Results

Linear regression models revealed the highest associations of the psychological factors with the PDI (adjusted R² = 0.296, p < 0.001, independent predictors: PCS, AEQ social avoidance, depression) followed by the MIDAS (adjusted R² = 0.137, p < 0.001, predictors: depression, AEQ social avoidance) and headache frequency (adjusted R² = 0.083, p < 0.001, predictors: depression, AEQ humor/distraction). Principal component analysis corroborated that psychological factors were preferentially associated with the PDI, while the MIDAS loaded together with headache frequency.

Conclusion

Our results suggest that psychological factors are more strongly associated with the subjective degree of headache-related disability measured by the PDI than with the days with disability (MIDAS) or the more objective parameter of headache frequency. This once again highlights the need for comprehensive assessment of migraine patients with different headache parameters and the need for considering psychological treatment, especially in patients with high disability.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10072-021-05453-2.

The Altered Functional Connectivity With Pain Features Integration and Interaction in Migraine Without Aura

Introduction

Migraine without aura (MwoA) is a primary type of migraine, a common disabling disorder, and a disabling neurological condition. The headache is a complex experience, a common form of pain, in which multiple sensory information dimensions are combined to provide a unified conscious event. Migraine ictal have unique neuroimage biomarkers, but the brain is also affected during the inter-ictal phase. According to the current studies, a hypothesis was constructed that the altered integration of pain spatial and intensity information impacts headache intensity in the inter-ictal period.

Methods

In this study, we applied theory-based region-to-region functional connectivity (FC) analyses to compare the differences in resting-state FC between MwoA participants and healthy controls with the pain integration hypothesis. After the correlation matrices between FC edges and clinical symptoms were constructed, the moderating effect and simple slope tests were investigated to explain whether and how the dysfunction of pain features discrimination affects the clinical symptoms.

Results

Functional connectivity analyses showed significantly decreased FC edges between the left dorsolateral superior frontal gyrus (SFGdor) and left insula, and an increased FC edge between the left SFGdor and bilateral angular gyrus. The correlation matrix showed no significant correlation between significantly altered FC edge and headache duration, frequency, Zung self-rating anxiety scale, and Zung self-rating depression scale. Only one significantly altered edge in the MwoA condition was significantly correlated with headache intensity. Moderating Module 1 and 2 manifested the moderator variable (altered rs-FC edge) moderated the link between the normal edges and headache intensity.

Conclusion

The pain features integration processes in migraineurs vary from HCs, related to the clinical symptoms during a migraine attack. Moreover, the clinical symptoms will be affected by one or more discrimination modules. And the spatial or intensity discrimination modules have a higher impact when combined with another module on clinical symptoms than the single module.

Migraine treatment and the risk of postoperative, pain-related hospital readmissions in migraine patients

BACKGROUND

Migraine treatment may mitigate migraine and associated pain in the perioperative period.

OBJECTIVE

The aim of the study was to estimate the effect of perioperative acute and prophylactic migraine treatment on the risk of postoperative 30-day hospital readmission with an admitting diagnosis specifying any pain complaints among migraine patients.

DESIGN

Electronic health records were analysed for 21,932 adult migraine patients undergoing surgery between 2005 and 2017 at Beth Israel Deaconess Medical Center and Massachusetts General Hospital in Boston, Massachusetts, USA.

METHODS

Perioperative abortive migraine treatment was defined as guideline-recommended medication (triptan, ergotamine, acetaminophen, nonsteroidal anti-inflammatory drug) prescription after surgery, within 30 days after discharge and prior readmission. Perioperatively continued prophylactic migraine treatment was defined as prescription both prior to surgery and perioperatively for recommended medications (beta-blockers, antidepressants, antiepileptics, onabotulinumtoxin A).

RESULTS

Overall, 10,921 (49.8%) patients received a prescription for abortive migraine drugs. Of these, 1.2% and 1.5% of patients with and without such prescription were readmitted for pain, respectively. Patients with abortive treatment had lower odds of pain-related readmission (adjusted odds ratio 0.63 [95% confidence interval 0.49-0.81]). Prophylactic migraine treatment showed no effect on pain-related readmission independently of acute treatment (adjusted odds ratio 0.97 [95% confidence interval 0.72-1.32]).

CONCLUSIONS

Migraine patients undergoing surgery with a perioperative prescription for abortive migraine drugs were at decreased risk of pain-related hospital readmission.

Regional volume changes of the brain in migraine chronification

The pathophysiology of migraine is complex. Neuroimaging studies reveal functional and structural changes in the brains of migraine patients. We sought to explore regional volume differences in intracranial structures in patients with episodic and chronic migraine. Sixteen episodic migraine patients, 16 chronic migraine patients, and 24 normal controls were recruited and underwent 3.0 T MRI scanning. The volumes of 142 brain regions were calculated by an automatic volumetric algorithm and compared with clinical variables. Results demonstrated that the volumes of specific regions in the frontal and occipital lobes, and the right putamen, were increased and the volume of the fourth ventricle was decreased in the episodic migraine patients compared with controls. The volumes of the left basal forebrain, optic chiasm, and, the fourth ventricle were decreased in the chronic migraine patients, while the occipital cortex and the right putamen were larger. Compared to episodic migraine patiants, chronic migraine patients displayed larger left thalamus and smaller frontal regions. Correlation analysis showed that headache frequency was negatively correlated with the volume of the right frontal pole, right lateral orbital gyrus, and medial frontal lobes and positively correlated with the volume of the left thalamus. The sleep disturbance score was negatively correlated with the volume of the left basal forebrain. This suggests that migraine patients have structural changes in regions associated with pain processing and modulation, affective and cognitive processing, and visual perception. The remodeling of selective intracranial structures may be involved in migraine attacks. This study was approved by the Ethics Committee of Chinese PLA General Hospital (approval No. S2018-027-02) on May 31, 2018.

Sensory Modulation Disorder (SMD) and Pain: A New Perspective

Sensory modulation disorder (SMD) affects sensory processing across single or multiple sensory systems. The sensory over-responsivity (SOR) subtype of SMD is manifested clinically as a condition in which non-painful stimuli are perceived as abnormally irritating, unpleasant, or even painful. Moreover, SOR interferes with participation in daily routines and activities (Dunn, 2007; Bar-Shalita et al., 2008; Chien et al., 2016), co-occurs with daily pain hyper-sensitivity, and reduces quality of life due to bodily pain. Laboratory behavioral studies have confirmed abnormal pain perception, as demonstrated by hyperalgesia and an enhanced lingering painful sensation, in children and adults with SMD. Advanced quantitative sensory testing (QST) has revealed the mechanisms of altered pain processing in SOR whereby despite the existence of normal peripheral sensory processing, there is enhanced facilitation of pain-transmitting pathways along with preserved but delayed inhibitory pain modulation. These findings point to central nervous system (CNS) involvement as the underlying mechanism of pain hypersensitivity in SOR. Based on the mutual central processing of both non-painful and painful sensory stimuli, we suggest shared mechanisms such as cortical hyper-excitation, an excitatory-inhibitory neuronal imbalance, and sensory modulation alterations. This is supported by novel findings indicating that SOR is a risk factor and comorbidity of chronic non-neuropathic pain disorders. This is the first review to summarize current empirical knowledge investigating SMD and pain, a sensory modality not yet part of the official SMD realm. We propose a neurophysiological mechanism-based model for the interrelation between pain and SMD. Embracing the pain domain could significantly contribute to the understanding of this condition’s pathogenesis and how it manifests in daily life, as well as suggesting the basis for future potential mechanism-based therapies.

Visually induced analgesia during face or limb stimulation in healthy and migraine subjects

Background

Visually induced analgesia (VIA) defines a phenomenon in which viewing one’s own body part during its painful stimulation decreases the perception of pain. VIA occurs during direct vision of the stimulated body part and also when seeing it reflected in a mirror. To the best of our knowledge, VIA has not been studied in the trigeminal area, where it could be relevant for the control of headache.

Subjects and methods

We used heat stimuli (53°C) to induce pain in the right forehead or wrist in 11 healthy subjects (HSs) and 14 female migraine without aura (MO) patients between attacks. The subjects rated pain on a visual analog scale (VAS) and underwent contact heat-evoked potential (CHEP) recordings (five sequential blocks of four responses) with or without observation of their face/wrist in a mirror.

Results

During wrist stimulation, amplitude of the first block of P1–P2 components of CHEPs decreased compared to that in the control recording when HSs were seeing their wrist reflected in the mirror (p = 0.036; Z = 2.08); however, this was not found in MO patients. In the latter, the VAS pain score increased viewing the reflected wrist (p = 0.049; Z = 1.96). Seeing their forehead reflected in the mirror induced a significant increase in N2 latency of CHEPs in HSs, as well as an amplitude reduction in the first block of P1–P2 components of CHEPs both in HSs (p = 0.007; Z = 2.69) and MO patients (p = 0.035; Z = 2.10). Visualizing the body part did not modify habituation of CHEP amplitudes over the five blocks of averaged responses, neither during wrist nor during forehead stimulation.

Conclusion

This study adds to the available knowledge on VIA and demonstrates this phenomenon for painful stimuli in the trigeminal area, as long as CHEPs are used as indices of central pain processing. In migraine patients during interictal periods, VIA assessed with CHEPs is within normal limits in the face but absent at the wrist, possibly reflecting dysfunctioning of extracephalic pain control.

Role of the Prefrontal Cortex in Pain Processing

The prefrontal cortex (PFC) is not only important in executive functions, but also pain processing. The latter is dependent on its connections to other areas of the cerebral neocortex, hippocampus, periaqueductal gray (PAG), thalamus, amygdala, and basal nuclei. Changes in neurotransmitters, gene expression, glial cells, and neuroinflammation occur in the PFC during acute and chronic pain, that result in alterations to its structure, activity, and connectivity. The medial PFC (mPFC) could serve dual, opposing roles in pain: (1) it mediates antinociceptive effects, due to its connections with other cortical areas, and as the main source of cortical afferents to the PAG for modulation of pain. This is a ‘loop’ where, on one side, a sensory stimulus is transformed into a perceptual signal through high brain processing activity, and perceptual activity is then utilized to control the flow of afferent sensory stimuli at their entrance (dorsal horn) to the CNS. (2) It could induce pain chronification via its corticostriatal projection, possibly depending on the level of dopamine receptor activation (or lack of) in the ventral tegmental area-nucleus accumbens reward pathway. The PFC is involved in biopsychosocial pain management. This includes repetitive transcranial magnetic stimulation, transcranial direct current stimulation, antidepressants, acupuncture, cognitive behavioral therapy, mindfulness, music, exercise, partner support, empathy, meditation, and prayer. Studies demonstrate the role of the PFC during placebo analgesia, and in establishing links between pain and depression, anxiety, and loss of cognition. In particular, losses in PFC grey matter are often reversible after successful treatment of chronic pain.

Assessment of Responsiveness to Everyday Non-Noxious Stimuli in Pain-Free Migraineurs With Versus Without Aura

Migraineurs with aura (MWA) express higher interictal response to non-noxious and noxious experimental sensory stimuli compared with migraineurs without aura (MWoA), but whether these differences also prevail in response to everyday non-noxious stimuli is not yet explored. This is a cross-sectional study testing 53 female migraineurs (30 MWA; 23 MWoA) who underwent a wide battery of noxious psychophysical testing at a pain-free phase, and completed a Sensory Responsiveness Questionnaire and pain-related psychological questionnaires. The MWA group showed higher questionnaire-based sensory over-responsiveness (P = .030), higher magnitude of pain temporal summation (P = .031) as well as higher monthly attack frequency (P = .027) compared with the MWoA group. Overall, 45% of migraineurs described abnormal sensory (hyper- or hypo-) responsiveness; its incidence was higher among MWA (19 of 30, 63%) versus MWoA (6 of 23, 27%, P = .012), with an odds ratio of 3.58 for MWA. Sensory responsiveness scores were positively correlated with attack frequency (r = .361, P = .008) and temporal summation magnitude (r = .390, P = .004), both regardless of migraine type. MWA express higher everyday sensory responsiveness than MWoA, in line with higher response to experimental noxious stimuli. Abnormal scores of sensory responsiveness characterize people with sensory modulation dysfunction, suggesting possible underlying mechanisms overlap, and possibly high incidence of both clinical entities.

PERSPECTIVE

This article presents findings distinguishing MWA, showing enhanced pain amplification, monthly attack frequency, and over-responsiveness to everyday sensations, compared with MWoA. Further, migraine is characterized by a high incidence of abnormal responsiveness to everyday sensation, specifically sensory over-responsiveness, that was also found related to pain.

Exploring resting-state EEG complexity before migraine attacks

Objective

Entropy-based approaches to understanding the temporal dynamics of complexity have revealed novel insights into various brain activities. Herein, electroencephalogram complexity before migraine attacks was examined using an inherent fuzzy entropy approach, allowing the development of an electroencephalogram-based classification model to recognize the difference between interictal and preictal phases.

Methods

Forty patients with migraine without aura and 40 age-matched normal control subjects were recruited, and the resting-state electroencephalogram signals of their prefrontal and occipital areas were prospectively collected. The migraine phases were defined based on the headache diary, and the preictal phase was defined as within 72 hours before a migraine attack.

Results

The electroencephalogram complexity of patients in the preictal phase, which resembled that of normal control subjects, was significantly higher than that of patients in the interictal phase in the prefrontal area (FDR-adjusted p < 0.05) but not in the occipital area. The measurement of test-retest reliability (n = 8) using the intra-class correlation coefficient was good with r1 = 0.73 ( p = 0.01). Furthermore, the classification model, support vector machine, showed the highest accuracy (76 ± 4%) for classifying interictal and preictal phases using the prefrontal electroencephalogram complexity.

Conclusion

Entropy-based analytical methods identified enhancement or “normalization” of frontal electroencephalogram complexity during the preictal phase compared with the interictal phase. This classification model, using this complexity feature, may have the potential to provide a preictal alert to migraine without aura patients.

Role of the Attachment Style in Determining the Association Between Headache Features and Psychological Symptoms in Migraine Children and Adolescents. An Analytical Observational Case-Control Study

OBJECTIVE

We aimed to study the role of attachment style on headache severity and psychological symptoms in migraineurs children/adolescents. Moreover, we investigated the association between attachment style, migraine severity, and psychological symptoms.

BACKGROUND

Attachment theory suggests that early interpersonal relationships may be important determinants of psychopathology and pain management. In particular, individuals with insecure attachment styles have been shown to experience more pain than people with secure attachment style. Few studies focused on headache and data on attachment style in pediatric headache are scarce.

METHODS

We studied 90 migraineurs (mean age 12.2 ± 2.6 years; female: 54, male: 36). Patients were divided in two groups according to headache attack frequency: (1) high frequency (HF) patients, having from weekly to daily episodes and (2) low frequency (LF) patients, showing ≤3 episodes per month. According to headache attack intensity, patients were classified in two groups: (1) mild pain (MP), allowing the patient to continue his/her daily activities and (2) severe pain (SP), leading to interruption of patient activities or forcing the child to go to bed. The psychological screening was assessed by SAFA Anxiety, Depression, and Somatization questionnaires. Attachment style was measured by the semi-projective test Separation Anxiety Test. Patients were divided into "secure," "avoidant," "ambivalent," and "disorganized/confused" attachment patterns.

RESULTS

We found a significant relationship between the attachment style and migraine features. The ambivalent attachment was the most common style among patients reporting high attack frequency (51%) and severe pain intensity (50%). Anxiety (SAFA-A Tot: F = 23.3, P < .001), depression (SAFA-D Tot: F = 11.8, P < .001), and somatization (SAFA-S Tot: F = 10.1, P < .001) were higher in patients with ambivalent attachment style. Moreover, our results showed an association between high attack frequency and high anxiety levels, in children with ambivalent attachment style (F = 6.7, P < .002).

CONCLUSIONS

Ambivalent attachment style may be a common vulnerability factor that impacts on pain severity, anxiety, depression, and somatization symptoms in young migraineurs. In particular, the present study provides the first evidence of the role of insecure attachment on the relationship between pain severity and psychological symptoms in migraine children.

Functional Connectivity of EEG Signals Under Laser Stimulation in Migraine

In previous studies, migraine patients showed abnormalities in pain-related evoked responses, as reduced habituation to repetitive stimulation. In this study, we aimed to apply a novel analysis of EEG bands synchronization and directed dynamical influences under painful stimuli in migraine patients compared to non-migraine healthy volunteers. Thirty-one migraine without aura outpatients (MIGR) were evaluated and compared to 19 controls (CONT). The right hand was stimulated by means of 30 consecutive CO₂ laser stimuli. EEG signal was examined by means of Morlet wavelet, synchronization entropy (SE), and Granger causality (GC), and the statistically validated results were mapped on the corresponding scalp locations. The vertex complex of averaged laser-evoked responses (LEPs) showed reduced habituation compared to CONT. In the prestimulus phase, enhanced SE in the 0, 5–30 Hz range was present in MIGR and CONT between the bilateral temporal–parietal and the frontal regions around the midline. Migraine patients showed an anticipation of EEG changes preceding the painful stimulation compared to CONT. In the poststimulus phase, the same cortical areas were more connected in MIGR vs CONT. In both groups of patients and CONT, the habituation index was negatively correlated with the GC scores. A different pattern of cortical activation after painful stimulation was present in migraine. The increase in cortical connections during repetitive painful stimulation may subtend the phenomenon of LEPs reduced habituation. Brain network analysis may give an aid in understanding subtle changes of pain processing under laser stimuli in migraine patients.

Contact heat evoked potentials and habituation measured interictally in migraineurs

BACKGROUND

A lack of habituation of different evoked potential modalities in migraine patients in-between attacks has been suggested.

METHODS

This study investigates cortical response after painful stimuli evaluated by contact heat evoked potentials (CHEPs) and quantitative sensory testing (QST) during the migraine-free interval. We enrolled 22 migraine patients and 22 healthy subjects.

RESULTS

Cortical potentials after contact heat stimulation of the cheeks and the volar forearm at a temperature of 51°C showed significantly reduced A-δ-amplitudes in patients and healthy controls. When the subjects' attention was drawn to an arithmetic task, a partial lack of habituation of amplitude could be seen in migraine patients. QST did not show any difference between migraineurs and controls.

CONCLUSION

Our findings can be primarily deemed to demonstrate that patients and healthy controls show significantly lower amplitudes while performing the calculation task. Without performing the calculation task we could not show the expected lack of habituation in migraineurs. Yet, while performing the calculation task our results partly suggest that hypothesis.

Correlations between brain cortical thickness and cutaneous pain thresholds are atypical in adults with migraine

BACKGROUND/OBJECTIVE

Migraineurs have atypical pain processing, increased expectations for pain, and hypervigilance for pain. Recent studies identified correlations between brain structure and pain sensation in healthy adults. The objective of this study was to compare cortical thickness-to-pain threshold correlations in migraineurs to healthy controls. We hypothesized that migraineurs would have aberrant relationships between the anatomical neurocorrelates of pain processing and pain thresholds.

METHODS

Pain thresholds to cutaneously applied heat were determined for 31 adult migraineurs and 32 healthy controls. Cortical thickness was determined from magnetic resonance imaging T1-weighted sequences. Regional cortical thickness-to-pain threshold correlations were determined for migraineurs and controls separately using a general linear model whole brain vertex-wise analysis. A pain threshold-by-group interaction analysis was then conducted to estimate regions where migraineurs show alterations in the pain threshold-to-cortical thickness correlations relative to healthy controls.

RESULTS

Controls had negative correlations (p<0.01 uncorrected) between pain thresholds and cortical thickness in left posterior cingulate/precuneus, right superior temporal, right inferior parietal, and left inferior temporal regions, and a negative correlation (p<0.01 Monte Carlo corrected) with a left superior temporal/inferior parietal region. Migraineurs had positive correlations (p<0.01 uncorrected) between pain thresholds and cortical thickness in left superior temporal/inferior parietal, right precuneus, right superior temporal/inferior parietal, and left inferior parietal regions. Cortical thickness-to-pain threshold correlations differed between migraine and control groups (p<0.01 uncorrected) for right superior temporal/inferior parietal, right precentral, left posterior cingulate/precuneus, and right inferior parietal regions and (p<0.01 Monte Carlo corrected) for a left superior temporal/inferior parietal region.

CONCLUSIONS

Unlike healthy control subjects who have a significant negative correlation between cortical thickness in a superior temporal/inferior parietal region with pain thresholds, migraineurs have a non-significant positive correlation between cortical thickness in a superior temporal/inferior parietal region with pain thresholds. Since this region participates in orienting and attention to painful stimuli, absence of the normal correlation might represent a migraineurs inability to inhibit pain sensation via shifting attention away from the painful stimulus.

Enhanced pain-induced activity of pain-processing regions in a case-control study of episodic migraine

OBJECTIVE

The objective of this study was to identify brain regions having aberrant pain-induced activation in migraineurs, thereby gaining insight into particular aspects of pain processing that are atypical in migraineurs.

METHODS

Functional magnetic resonance imaging assessed whole brain responses to painful heat in 24 adult episodic migraineurs who were at least 48 hours pain free and 27 healthy controls. Regions differentially activated in migraineurs compared to controls were identified. Activation intensities in these regions were correlated with headache frequency, number of migraine years, and time to next migraine attack.

RESULTS

Migraineurs had greater pain-induced activation of lentiform nucleus, fusiform gyrus, subthalamic nucleus, hippocampus, middle cingulate cortex, premotor cortex, somatosensory cortex, and dorsolateral prefrontal cortex, and less activation in precentral gyrus and superior temporal gyrus. There were significant correlations between activation strength and headache frequency for middle cingulate (r = 0.627, p = 0.001), right dorsolateral prefrontal cortex (r = 0.568, p = 0.004), left fusiform gyrus (r = 0.487, p = 0.016), left precentral gyrus (r = 0.415, p = 0.044), and left hippocampus (r = 0.404, p = 0.050) and with number of migraine years for left fusiform gyrus (r = 0.425, p = 0.038). There were no significant correlations between activation strength and time to next migraine attack.

CONCLUSIONS

The majority of regions with enhanced pain-induced activation in headache-free migraineurs participate in cognitive aspects of pain perception such as attending to pain and pain memory. Enhanced cognitive pain processing by migraineurs might reflect cerebral hypersensitivity related to high expectations and hypervigilance for pain.

Altered processing of sensory stimuli in patients with migraine

Migraine is a cyclic disorder, in which functional and morphological brain changes fluctuate over time, culminating periodically in an attack. In the migrainous brain, temporal processing of external stimuli and sequential recruitment of neuronal networks are often dysfunctional. These changes reflect complex CNS dysfunction patterns. Assessment of multimodal evoked potentials and nociceptive reflex responses can reveal altered patterns of the brain's electrophysiological activity, thereby aiding our understanding of the pathophysiology of migraine. In this Review, we summarize the most important findings on temporal processing of evoked and reflex responses in migraine. Considering these data, we propose that thalamocortical dysrhythmia may be responsible for the altered synchronicity in migraine. To test this hypothesis in future research, electrophysiological recordings should be combined with neuroimaging studies so that the temporal patterns of sensory processing in patients with migraine can be correlated with the accompanying anatomical and functional changes.

Does attachment anxiety increase vulnerability to headache?

BACKGROUND

Attachment-related anxiety and avoidance are potentially important aspects of pain experience and management, but have not been investigated in episodic headache sufferers or in relation to experimentally-evoked headache.

OBJECTIVE

To determine whether adult insecure attachment styles were associated with sensitivity to pain or headache before, during or after stressful mental arithmetic in an episodic migraine or tension-type headache (T-TH) sample.

METHODS

Thirty-eight participants with episodic migraine, 28 with episodic T-TH and 20 headache-free participants intermittently received a mild electric shock to the forehead before, during and after stressful mental arithmetic.

RESULTS

A preoccupied attachment style and attachment anxiety, but not attachment avoidance, were associated with forehead pain and the intensity of headache before and after, but not during stressful mental arithmetic. These relationships were independent of Five Factor Model personality traits. Neither attachment anxiety nor avoidance was associated with episodic migraine or T-TH.

CONCLUSIONS

Anxiously attached individuals may express greater pain or show a stronger attentional bias toward painful sensations than securely attached individuals. However, distraction during psychological stress may override this attentional bias.

Habituation and sensitization in primary headaches

The phenomena of habituation and sensitization are considered most useful for studying the neuronal substrates of information processing in the CNS. Both were studied in primary headaches, that are functional disorders of the brain characterized by an abnormal responsivity to any kind of incoming innocuous or painful stimuli and it's cycling pattern over time (interictal, pre-ictal, ictal). The present review summarizes available data on stimulus responsivity in primary headaches obtained with clinical neurophysiology. In migraine, the majority of electrophysiological studies between attacks have shown that, for a number of different sensory modalities, the brain is characterised by a lack of habituation of evoked responses to repeated stimuli. This abnormal processing of the incoming information reaches its maximum a few days before the beginning of an attack, and normalizes during the attack, at a time when sensitization may also manifest itself. An abnormal rhythmic activity between thalamus and cortex, namely thalamocortical dysrhythmia, may be the pathophysiological mechanism subtending abnormal information processing in migraine. In tension-type headache (TTH), only few signs of deficient habituation were observed only in subgroups of patients. By contrast, using grand-average responses indirect evidence for sensitization has been found in chronic TTH with increased nociceptive specific reflexes and evoked potentials. Generalized increased sensitivity to pain (lower thresholds and increased pain rating) and a dysfunction in supraspinal descending pain control systems may contribute to the development and/or maintenance of central sensitization in chronic TTH. Cluster headache patients are characterized during the bout and on the headache side by a pronounced lack of habituation of the brainstem blink reflex and a general sensitization of pain processing. A better insight into the nature of these ictal/interictal electrophysiological dysfunctions in primary headaches paves the way for novel therapeutic targets and may allow a better understanding of the mode of action of available therapies.