Interictal habituation deficit of the nociceptive blink reflex: an endophenotypic marker for presymptomatic migraine?

The blink reflex and its modulation - Part 2: Pathophysiology and clinical utility

The blink reflex (BR) is integrated at the brainstem; however, it is modulated by inputs from various structures such as the striatum, globus pallidus, substantia nigra, and nucleus raphe magnus but also from afferent input from the peripheral nervous system. Therefore, it provides information about the pathophysiology of numerous peripheral and central nervous system disorders. The BR is a valuable tool for studying the integrity of the trigemino-facial system, the relevant brainstem nuclei, and circuits. At the same time, some neurophysiological techniques applying the BR may indicate abnormalities involving structures rostral to the brainstem that modulate or control the BR circuits. This is a state-of-the-art review of the clinical application of BR modulation; physiology is reviewed in part 1. In this review, we aim to present the role of the BR and techniques related to its modulation in understanding pathophysiological mechanisms of motor control and pain disorders, in which these techniques are diagnostically helpful. Furthermore, some BR techniques may have a predictive value or serve as a basis for follow-up evaluation. BR testing may benefit in the diagnosis of hemifacial spasm, dystonia, functional movement disorders, migraine, orofacial pain, and psychiatric disorders. Although the abnormalities in the integrity of the BR pathway itself may provide information about trigeminal or facial nerve disorders, alterations in BR excitability are found in several disease conditions. BR excitability studies are suitable for understanding the common pathophysiological mechanisms behind various clinical entities, elucidating alterations in top-down inhibitory systems, and allowing for follow-up and quantitation of many neurological syndromes.

Exploring the cortical habituation in migraine patients based on contingent negative variation

Introduction

Cognitive dysfunction has frequently been found in patients with migraine. The so-called contingent negative variation (CNV) and EEG power spectral densities may be the best choices to explore the underlining pathophysiology, such as cortical inhibition and habituation.

Methods

Thirty migraine patients without aura and healthy controls matched for sex, age, and education were recruited separately for CNV recording. The amplitudes, latencies, and squares of different CNV components, such as oCNV, iCNV, tCNV, and PINV, were selected and analyzed. Behavioral data, such as manual reaction time (RT), were analyzed. We used the Person correlation coefficient R to analyze different ERP components in relation to clinical characteristics. A multiple regression analysis was conducted for the migraine group. Spectral analysis of EEG data from all channels using the fast Fourier transform (FFT).

Results

The migraine group had longer A-latency, C-latency, and iCNV-latency than the control group. The migraine group had higher iCNV-amplitude, oCNV-amplitude, and tCNV-amplitude than the control group, especially those located in the occipital area. The iCNV-square, oCNV-square, tCNV-square, or PINV-square in the migraine group was significantly larger than the control group. Different correlations were found between clinical characteristics and ERP components. The delta or theta activity in the migraine group was statistically lower than in the control group.

Discussion

Our study has revealed that migraine attacks may influence responsivity, pre-activation, habituation, and cortical inhibition not only on the behavioral level but also on the electrophysiological level. Abnormal changes in cortical habituation and inhibition can be interpreted as CNV components. Additionally, analyses have revealed correlations between CNV components and various factors, including age, the clinical course of the condition, attack frequency, pain intensity, and duration. Thus, repetitive migraine attacks can lead to a reduction in cortical inhibition and subsequent impairment in executive function.

Effects of Botulinum Toxin Type A on the Nociceptive and Lemniscal Somatosensory Systems in Chronic Migraine: An Electrophysiological Study

(1) Background: OnabotulinumtoxinA (BoNT-A) is a commonly used prophylactic treatment for chronic migraine (CM). Although randomized placebo studies have shown its clinical efficacy, the mechanisms by which it exerts its therapeutic effect are still incompletely understood and debated. (2) Methods: We studied in 15 CM patients the cephalic and extracephalic nociceptive and lemniscal sensory systems using electrophysiological techniques before and 1 and 3 months after one session of pericranial BoNT-A injections according to the PREEMPT protocol. We recorded the nociceptive blink reflex (nBR), the trigemino-cervical reflex (nTCR), the pain-related cortical evoked potential (PREP), and the upper limb somatosensory evoked potential (SSEP). (3) Results: Three months after a single session of prophylactic therapy with BoNT-A in CM patients, we found (a) an increase in the homolateral and contralateral nBR AUC, (b) an enhancement of the contralateral nBR AUC habituation slope and the nTCR habituation slope, (c) a decrease in PREP N-P 1st and 2nd amplitude block, and (d) no effect on SSEPs. (4) Conclusions: Our study provides electrophysiological evidence for the ability of a single session of BoNT-A injections to exert a neuromodulatory effect at the level of trigeminal system through a reduction in input from meningeal and other trigeminovascular nociceptors. Moreover, by reducing activity in cortical pain processing areas, BoNT-A restores normal functioning of the descending pain modulation systems.

What has neurophysiology revealed about migraine and chronic migraine?

Since the first electroencephalographic recordings obtained by Golla and Winter in 1959, researchers have used a variety of neurophysiological techniques to determine the mechanisms underlying recurrent migraine attacks. Neurophysiological methods have shown that the brain during the interictal phase of an episodic migraine is characterized by a general hyperresponsiveness to sensory stimuli, a malfunction of the monoaminergic brainstem circuits, and by functional alterations of the thalamus and thalamocortical loop. All of these alterations vary plastically during the phases of the migraine cycle and interictally with the days following the attack. Both episodic migraineurs recorded during an attack and chronic migraineurs are characterized by a general increase in the cortical amplitude response to peripheral sensory stimuli; this is an electrophysiological hallmark of a central sensitization process that is further reinforced through medication overuse. Considering the large-scale functional involvement and the main roles played by the brainstem-thalamo-cortical network in selection, elaboration, and learning of relevant sensory information, future research should move from searching for one specific primary site of dysfunction at the macroscopic level, to the chronic, probably genetically determined, molecular dysfunctions at the synaptic level, responsible for short- and long-term learning mechanisms.

Impaired Pain Processing at a Brainstem Level Is Involved in Maladaptive Neuroplasticity in Patients with Chronic Complex Regional Pain Syndrome

Neuroinflammatory mechanisms and maladaptive neuroplasticity underlie the progression of complex regional pain syndrome (CRPS), which is prototypical of central neuropathic pain conditions. While cortical maladaptive alterations are well described, little is known about the contribution of the brainstem to the pathophysiology. This study investigates the role of pain-modulatory brainstem pathways in CRPS using the nociceptive blink reflex (nBR), which not only provides a direct read-out of brainstem excitability and habituation to painful stimuli but may also be suitable for use as a diagnostic biomarker for CRPS. Thirteen patients with CRPS and thirteen healthy controls (HCs) participated in this prospective case-control study investigating the polysynaptic trigemino-cervical (R2) nBR response. The R2 area and its habituation were assessed following repeated supraorbital electrical stimulation. Between-group comparisons included evaluations of diagnostic characteristics as a potential biomarker for the disease. Patients with CRPS showed a substantial decrease in habituation on the stimulated (Cohen's d: 1.3; p = 0.012) and the non-stimulated side (Cohen's d: 1.1; p = 0.04). This is the first study to reveal altered nBR habituation as a pathophysiological mechanism and potential diagnostic biomarker in CRPS. We confirmed previous findings of altered nBR excitability, but the diagnostic accuracy was inferior. Future studies should investigate the nBR as a marker of progression to central mechanisms in CRPS and as a biomarker to predict treatment response or prognosis.

Neurobiology of migraine progression

Chronic migraine is one of the most devastating headache disorders. The estimated prevalence is 1.4-2.2% in the population. The factors which may predispose to the process of migraine progression include high frequency of migraine attacks, medication overuse, comorbid pain syndromes, and obesity. Several studies showed that chronic migraine results in the substantial anatomical and physiological changes in the brain. Despite no clear explanation regarding the pathophysiologic process leading to the progression, certain features such as increased sensory sensitivity, cutaneous allodynia, impaired habituation, identify the neuronal hyperexcitability as the plausible mechanism. In this review, we describe two main mechanisms which can lead to this hyperexcitability. The first is persistent sensitization caused by repetitive and prolonged trigeminal nociceptive activation. This process results in changes in several brain networks related to both pain and non-pain behaviours. The second mechanism is the decrease in endogenous brainstem inhibitory control, hence increasing the excitability of neurons in the trigeminal noceptive system and cerebral cortex. The combination of increased pain matrix connectivity, including hypothalamic hyperactivity and a weak serotonergic system, may contribute to migraine chronification.

Expression of Selected microRNAs in Migraine: A New Class of Possible Biomarkers of Disease?

Preliminary but convergent findings suggest a role for microRNAs (miRNAs) in the generation and maintenance of chronic pain and migraine. Initial observations showed that serum levels of miR-382-5p and miR-34a-5p expression were increased in serum during the migraine attack, with miR-382-5p increasing in the interictal phase as well. By contrast, miR-30a-5p levels were lower in migraine patients compared to healthy controls. Of note, antimigraine treatments proved to be capable of influencing the expression of these miRNAs. Altogether, these observations suggest that miRNAs may represent migraine biomarkers, but several points are yet to be elucidated. A major concern is that these miRNAs are altered in a broad spectrum of painful and non-painful conditions, and thus it is not possible to consider them as truly “migraine-specific” biomarkers. We feel that these miRNAs may represent useful tools to uncover and define different phenotypes across the migraine spectrum with different treatment susceptibilities and clinical features, although further studies are needed to confirm our hypothesis. In this narrative review we provide an update and a critical analysis of available data on miRNAs and migraines in order to propose possible interpretations. Our main objective is to stimulate research in an area that holds promise when it comes to providing reliable biomarkers for theoretical and practical scientific advances.

Sensitized rotatory motion perception and increased susceptibility to motion sickness in vestibular migraine: A cross-sectional study

BACKGROUND AND PURPOSE

Vestibular migraine (VM) patients are ictally and interictally hypersensitive for self-motion and visual perception. Increased cortical excitability of the vestibular system represented by lowered motion perception thresholds might play an important role in the pathophysiology of VM. We aimed to compare motion perception thresholds and the vegetative response to rotatory motion, as well as the vestibulo-ocular reflex (VOR) during rotation in VM patients compared to healthy controls (HC).

METHODS

In this cross-sectional study, 28 female VM patients in the interictal state and 33 age- and gender-matched HC were investigated sitting in a motorized rotary chair shielded regarding visual and acoustic stimuli for 20 min with slowly increasing velocity (maximum = 72°/s). The motion perception threshold was indicated by the participants by pushing a button. During and after rotation, participants rated the presence and extent of motion sickness using a sickness rating scale.

RESULTS

We detected lower motion perception thresholds (7.54°/s vs. 23.49°/s; p < 0.001) in VM patients compared to HC but no difference at the basic VOR thresholds. Furthermore, the patients showed enhanced susceptibility to motion sickness during and after the rotation.

CONCLUSIONS

We provide evidence for decreased motion perception thresholds and pronounced susceptibility to motion sickness in VM patients in the interictal state, which could indicate alterations in higher levels of vestibular processing. Future studies should determine whether this could be the pathophysiological hallmark of VM either as a unique disease entity or in differentiation from other forms of migraine.

The visual system as target of non-invasive brain stimulation for migraine treatment: Current insights and future challenges

The visual network is crucially implicated in the pathophysiology of migraine. Several lines of evidence indicate that migraine is characterized by an altered visual cortex excitability both during and between attacks. Visual symptoms, the most common clinical manifestation of migraine aura, are likely the result of cortical spreading depression originating from the extrastriate area V3A. Photophobia, a clinical hallmark of migraine, is linked to an abnormal sensory processing of the thalamus which is converged with the non-image forming visual pathway. Finally, visual snow is an increasingly recognized persistent visual phenomenon in migraine, possibly caused by increased perception of subthreshold visual stimuli. Emerging research in non-invasive brain stimulation (NIBS) has vastly developed into a diversity of areas with promising potential. One of its clinical applications is the single-pulse transcranial magnetic stimulation (sTMS) applied over the occipital cortex which has been approved for treating migraine with aura, albeit limited evidence. Studies have also investigated other NIBS techniques, such as repetitive TMS (rTMS) and transcranial direct current stimulation (tDCS), for migraine prophylaxis but with conflicting results. As a dynamic brain disorder with widespread pathophysiology, targeting migraine with NIBS is challenging. Furthermore, unlike the motor cortex, evidence suggests that the visual cortex may be less plastic. Controversy exists as to whether the same fundamental principles of NIBS, based mainly on findings in the motor cortex, can be applied to the visual cortex. This review aims to explore existing literature surrounding NIBS studies on the visual system of migraine. We will first provide an overview highlighting the direct implication of the visual network in migraine. Next, we will focus on the rationale behind using NIBS for migraine treatment, including its effects on the visual cortex, and the shortcomings of currently available evidence. Finally, we propose a broader perspective of how novel approaches, the concept of brain networks and the integration of multimodal imaging with computational modeling, can help refine current NIBS methods, with the ultimate goal of optimizing a more individualized treatment for migraine.

Pearls and pitfalls in brain functional analysis by event-related potentials: a narrative review by the Italian Psychophysiology and Cognitive Neuroscience Society on methodological limits and clinical reliability-part I

Event-related potentials (ERPs) are obtained from the electroencephalogram (EEG) or the magnetoencephalogram (MEG, event-related fields (ERF)), extracting the activity that is time-locked to an event. Despite the potential utility of ERP/ERF in cognitive domain, the clinical standardization of their use is presently undefined for most of procedures. The aim of the present review is to establish limits and reliability of ERP medical application, summarize main methodological issues, and present evidence of clinical application and future improvement. The present section of the review focuses on well-standardized ERP methods, including P300, Contingent Negative Variation (CNV), Mismatch Negativity (MMN), and N400, with a chapter dedicated to laser-evoked potentials (LEPs). One section is dedicated to proactive preparatory brain activity as the Bereitschaftspotential and the prefrontal negativity (BP and pN). The P300 and the MMN potentials have a limited but recognized role in the diagnosis of cognitive impairment and consciousness disorders. LEPs have a well-documented usefulness in the diagnosis of neuropathic pain, with low application in clinical assessment of psychophysiological basis of pain. The other ERP components mentioned here, though largely applied in normal and pathological cases and well standardized, are still confined to the research field. CNV, BP, and pN deserve to be largely tested in movement disorders, just to explain possible functional changes in motor preparation circuits subtending different clinical pictures and responses to treatments.

Brain state monitoring for the future prediction of migraine attacks

BACKGROUND

Migraine attacks are unpredictable, precluding preemptive interventions and leading to lack of control over individuals' lives. Although there are neurophysiological changes 24-48 hours before migraine attacks, so far, they have not been used in patients' management. This study evaluates the applicability and the ability to identify pre-attack changes of daily "at home" electroencephalography obtained with a portable system for migraine patients.

METHODS

Patients with episodic migraine fulfilling ICHD-3 beta criteria used a mobile system composed of a wireless EEG device (BrainStation®, Neuroverse®, Inc., USA) and mobile application (BrainVitals_M®, Neuroverse®, Inc., USA) to self-record their neural activity daily at home while resting and while performing an attention task, over the course of 2 weeks. Standard EEG spectral analysis and event-related brain potentials (ERP) methods were used and recordings were grouped by time from migraine attacks (i.e. "Interictal day", "24 h Before Migraine", "Migraine day" and "Post Migraine").

RESULTS

Twenty-four patients (22 women) recorded an average of 13.3 ± 1.9 days and had 2 ± 0.9 attacks. Twenty-four hours before attack onset, there was a statistically significant modulation of relative power in the delta (decrease) and beta (increase) frequency bands, at rest, and a significant reduction of the amplitude and inter-trial coherence measures of an attention event-related brain potential (P300).

CONCLUSIONS

This proof-of-concept study shows that brain state monitoring, utilising an easy-to-use wearable EEG system to track neural modulations at home, can identify physiological changes preceding a migraine attack enabling valuable pre-symptom prediction and subsequent early intervention.

A ketogenic diet normalizes interictal cortical but not subcortical responsivity in migraineurs

Background

A short ketogenic diet (KD) treatment can prevent migraine attacks and correct excessive cortical response. Here, we aim to prove if the KD-related changes of cortical excitability are primarily due to cerebral cortex activity or are modulated by the brainstem.

Methods

Through the stimulation of the right supraorbital division of the trigeminal nerve, we concurrently interictally recorded the nociceptive blink reflex (nBR) and the pain-related evoked potentials (PREP) in 18 migraineurs patients without aura before and after 1-month on KD, while in metabolic ketosis. nBR and PREP reflect distinct brain structures activation: the brainstem and the cerebral cortex respectively. We estimated nBR R2 component area-under-the-curve as well as PREP amplitude habituation as the slope pof the linear regression between the 1st and the 2nd block of 5 averaged responses.

Results

Following 1-month on KD, the mean number of attacks and headache duration reduced significantly. Moreover, KD significantly normalized the interictal PREP habituation (pre: + 1.8, post: − 9.1, p = 0.012), while nBR deficit of habituation did not change.

Conclusions

The positive clinical effects we observed in a population of migraineurs by a 1-month KD treatment coexists with a normalization at the cortical level, not in the brainstem, of the typical interictal deficit of habituation. These findings suggest that the cerebral cortex may be the primary site of KD-related modulation.

Trial registration

ClinicalTrials.gov NCT03775252 (retrospectively registered, December 09, 2018).

Increased pain sensitivity but normal pain modulation in adolescents with migraine

Inhibitory pain modulation has been reported to be deficient in adults across different types of chronic pain, including migraine. To determine whether a similar phenomenon occurs in youth, we performed a quantitative sensory testing investigation in adolescents with migraine (N = 19). These patients were compared to healthy adolescents with (Fam-His; N = 20) or without (Healthy; N = 29) a family history of migraine (eg, first-degree relative with migraine). Subjects were first familiarized with the stimuli and visual analogue rating scales using graded noxious stimuli (0°C, 43-49°C range). These data were used to explore potential pain sensitivity differences between the groups. Pain inhibition was assessed by conditioned pain modulation (CPM), which used both suprathreshold heat pain (heat CPM) and pressure pain thresholds (pressure CPM) as the test stimuli before and during cold-water immersion (8°C). In response to the graded heat stimuli, Fam-His participants reported higher pain intensity ratings compared with patients with migraine, who in turn reported higher pain intensity ratings than the healthy controls (F = 3.6, [df = 2, 459], P = 0.027). For heat and pressure CPM, there was no significant group difference in the magnitude of CPM responses. Thus, adolescents with migraine and healthy adolescents have similar inhibitory pain modulation capability, despite having marked differences in pain sensitivity. Although Fam-His participants are asymptomatic, they demonstrate alterations in pain processing, which may serve as markers for prediction of migraine development.

Electrophysiological Characteristics of the Migraine Brain: Current Knowledge and Perspectives

BACKGROUND

Despite pain being its most prominent feature, migraine is primarily a disorder of sensory processing. Electrophysiology-based research in the field has consistently developed over the last fifty years.

OBJECTIVE

To summarize the current knowledge on the electrophysiological characteristics of the migraine brain, and discuss perspectives.

METHODS

We critically reviewed the literature on the topic to present and discuss articles selected on the basis of their significance and/or novelty.

RESULTS

Physiologic fluctuations within time, between-subject differences, and methodological issues account as major limitations of electrophysiological research in migraine. Nonetheless, several abnormalities revealed through different approaches have been described in the literature. Altogether, these results are compatible with an abnormal state of sensory processing.

PERSPECTIVES

The greatest contribution of electrophysiological testing in the future will most probably be the characterization of sub-groups of migraine patients sharing specific electrophysiological traits. This should serve as strategy towards personalized migraine treatment. Incorporation of novel methods of analysis would be worthwhile.

Nociceptive blink reflex habituation biofeedback in migraine

Reduced habituation of the nociceptive blink reflex (NBR) is considered a trait marker for genetic predisposition to migraine. In this open-label randomized controlled study, we aimed to test the efficacy of a biofeedback training based on learning of habituation of the NBR (NBR biofeedback) compared with pharmacological (topiramate) treatment and NBR biofeedback plus topiramate treatment in a cohort of migraine without aura patients eligible for prophylaxis. Thirty-three migraine patients were randomly assigned to three months of treatment with: 1) NBR biofeedback, 2) NBR biofeedback plus topiramate 50 mg (b.i.d.), or 3) topiramate 50 mg (b.i.d.). Frequency of headache and disability changes were the main study outcomes. Anxiety, depression, sleep, fatigue, quality of life, allodynia and pericranial tenderness were also evaluated. NBR biofeedback reduced the R2 area, without improving R2 habituation. However, it reduced the frequency of headache and disability, similarly to the combined treatment and topiramate alone. Reduced habituation of the NBR is a stable neurophysiological pattern, scarcely modifiable by learning procedures. Training methods able to act on stress-related responses may modulate cortical mechanisms inducing migraine onset and trigeminal activation under stressful trigger factors.

Increased Amplitude of Thalamocortical Low-Frequency Oscillations in Patients with Migraine

For many years, neurobiological theories have emphasized the importance of neuronal oscillations in the emergence of brain function. At the same time, clinical studies have shown that disturbances or irregularities in brain rhythms may relate to various common neurological conditions, including migraine. Increasing evidence suggests that the CNS plays a fundamental role in the predisposition to develop different forms of headache. Here, we present human imaging data that strongly support the presence of abnormal low-frequency oscillations (LFOs) in thalamocortical networks of patients in the interictal phase of migraine. Our results show that the main source of arrhythmic activity was localized to the higher-order thalamic relays of the medial dorsal nucleus. In addition, spontaneous LFOs in the thalamus were selectively associated with the headache attack frequency, meaning that the varying amplitude of dysrhythmia could predispose patients to recurrent attacks. Rhythmic cortical feedback to the thalamus is a major factor in the amplification of thalamocortical oscillations, making it a strong candidate for influencing neuronal excitability. We further speculate that the intrinsic dynamics of thalamocortical network oscillations are crucial for early sensory processing and therefore could underlie important pathophysiological processes involved in multisensory integration.

SIGNIFICANCE STATEMENT

In many cases, migraine attacks are thought to begin centrally. A major obstacle to studying intrinsic brain activity has been the identification of the precise anatomical structures and functional networks that are involved in migraine. Here, we present imaging data that strongly support the presence of abnormal low-frequency oscillations in thalamocortical networks of patients in the interictal phase of migraine. This arrhythmic activity was localized to the higher-order thalamic relays of the medial dorsal nucleus and was selectively associated with headache attack frequency. Rhythmic cortical feedback to the thalamus is a major factor in the amplification of thalamocortical oscillations, making it a strong candidate for influencing neuronal excitability and higher-level processes involved in multisensory integration.

Frequency-Dependent Habituation Deficit of the Nociceptive Blink Reflex in Aura With Migraine Headache. Can Migraine Aura Modulate Trigeminal Excitability?

OBJECTIVE

To study the influence of the migraine aura on the trigeminal nociception, we investigated the habituation of the nociceptive blink reflex (nBR) R2 responses in aura with migraine headache (AwMH) and comparatively in migraine without aura (MWoA) and healthy subjects (HS).

BACKGROUND

A clear deficit of habituation in trigeminal nociceptive responses has been documented in MWoA; however, similar data in MWA are lacking.

METHODS

Seventeen AwMH, 29 MWoA, and 30 HS were enrolled and a nonrandomized clinical neurophysiological study examining nBR habituation by clinical diagnosis was devised. We delivered a series of 26 electrical stimuli, at different stimulation frequencies (SF) (0.05, 0.1, 0.2, 0.3, 0.5, and 1 Hz), subsequently subdivided in five blocks of five responses for each SF. The mean area values of the second to the fifth block expressed as the percentage of the mean area value of the first block were taken as an index of habituation for each SF.

RESULTS

A significant lower mean percentage decrease of the R2 area across all blocks was found at 1, 0.5, 0.3, and 0.2 Hz SF in MWoA and at 0.3 and 0.2 Hz SF in AwMH, when compared to HS. In the most representative fifth block of responses, we found in MWoA vs HS at 1 Hz, 57.0 ± 27.8 vs 30.6 ± 12.0; at 0.5 Hz, 54.8 ± 26.1 vs 32.51 ± 17.7; at 0.3 Hz, 44.7 ± 21.6 vs 27.6 ± 13.2; at 0.2 Hz, 61.3 ± 29.5 vs 32.6 ± 18.0, and in AwMH vs HS at 0.3 Hz, 52.7 ± 24.7 vs 27.6 ± 13.2; at 0.2 Hz, 69.3 ± 38.6 vs 32.6 ± 18.0 as mean ± SD of the R2 area percentage of the first block, respectively. Interestingly, AwMH subjects did not show differences in mean percentage decrease of the R2 area at 1 and 0.5 Hz SF when compared to HS. No differences between groups were found at 0.1 and 0.05 Hz SF.

CONCLUSIONS

We demonstrated in AwMH a deficit of habituation of the nBR R2 responses after repeated stimulations, although less pronounced than that observed in MWoA of comparable clinical severity. We hypothesize that AwMH and MWoA share some pathogenetic aspects, and also that migraine aura physiopathology may play a modulating role on the excitability of the nociceptive trigeminal pathways.

Pathophysiology of Migraine: A Disorder of Sensory Processing

Plaguing humans for more than two millennia, manifest on every continent studied, and with more than one billion patients having an attack in any year, migraine stands as the sixth most common cause of disability on the planet. The pathophysiology of migraine has emerged from a historical consideration of the "humors" through mid-20th century distraction of the now defunct Vascular Theory to a clear place as a neurological disorder. It could be said there are three questions: why, how, and when? Why: migraine is largely accepted to be an inherited tendency for the brain to lose control of its inputs. How: the now classical trigeminal durovascular afferent pathway has been explored in laboratory and clinic; interrogated with immunohistochemistry to functional brain imaging to offer a roadmap of the attack. When: migraine attacks emerge due to a disorder of brain sensory processing that itself likely cycles, influenced by genetics and the environment. In the first, premonitory, phase that precedes headache, brain stem and diencephalic systems modulating afferent signals, light-photophobia or sound-phonophobia, begin to dysfunction and eventually to evolve to the pain phase and with time the resolution or postdromal phase. Understanding the biology of migraine through careful bench-based research has led to major classes of therapeutics being identified: triptans, serotonin 5-HT1B/1D receptor agonists; gepants, calcitonin gene-related peptide (CGRP) receptor antagonists; ditans, 5-HT1F receptor agonists, CGRP mechanisms monoclonal antibodies; and glurants, mGlu5 modulators; with the promise of more to come. Investment in understanding migraine has been very successful and leaves us at a new dawn, able to transform its impact on a global scale, as well as understand fundamental aspects of human biology.

Familial history of migraine influences habituation of visual evoked potentials

Background

Lack of habituation of visual evoked potentials (VEP) is a common finding in migraine patients between attacks. Previous studies have suggested an electrophysiological familial aggregation pattern associated with migraine. The aim of this study was to evaluate the influence of a positive familial history of migraine on VEP amplitude and habituation.

Methods

We recorded six blocks of 100 VEP during continuous pattern-reversal stimulation in 30 patients with migraine between attacks (MO) and in 30 healthy volunteers, of whom 15 had a first-degree relative suffering from migraine (HVm) and 15 had not (HV).

Results

Both MO and HVm had a significant deficit of VEP habituation and similarly reduced N1-P1 first block amplitudes, compared to HV (habituation slope: MO = 0.033, HVm = 0.021, HV = −0.025, HV vs. MO p = 0.002, HV vs. HVm p = 0.036; mean N1-P1 amplitude in the first block: MO = 9.08 µV, HVm = 9.29 µV, HV = 12.19 µV. HV vs. MO p = 0.041, HV vs. HVm p = 0.076). The first block N1-P1 amplitude was negatively correlated with the habituation slope for both MO (ρ = −.44, p = 0.015) and HVm (ρ = −.56, p = 0.031) while no significant correlation was found in HV (ρ = .17, p = 0.53). There were no differences in VEP latencies between the groups.

Conclusions

Our study suggests that lack of habituation of visual evoked potentials is probably a genetically determined endophenotypic trait that is associated with both migraine and migraine susceptibility. We hypothesize that genetic diversity of populations could account for some of the discrepancies between electrophysiological studies performed in migraine and for interindividual variations among the subgroups.

Deficient prepulse inhibition of blink reflex in migraine and its relation to allodynia

OBJECTIVE

Prepulse inhibition (PPI) of the blink reflex (BR) is a reduction in BR excitability due to a conditioning stimulus, reflecting sensory gating by brainstem structures. We aimed to analyze PPI changes during a painful episode in chronic or episodic migraine and its relation to allodynia, since abnormal brainstem filtering has been hypothesized in migraine pathophysiology.

METHODS

We included 20 patients with migraine during headache episode, and age- and gender-matched 22 healthy subjects. We recorded BR after unconditioned and conditioned supraorbital stimuli. For conditioned stimuli, we applied preceding subthreshold stimulus to the median nerve at wrist. The presence of PPI was compared between the two groups, as well as the specific BR parameters (latency, amplitude or area of R1 and R2 components) in unconditioned (test) and conditioned (PPI) paradigms.

RESULTS

In the patient group, seven (35%) patients did not have R2-PPI whereas all healthy subjects had R2-PPI (P=0.003). Healthy subjects displayed significantly increased R1 amplitude and reduced R2 amplitude and area after conditioned stimuli. In migraine patients, we observed significant reduction only in R2 amplitude. Logistic regression demonstrated that allodynia was independently related with the presence of PPI (beta: -0.535, P=0.021).

CONCLUSIONS

Our study provides evidence for sensory gating impairment at brainstem level in migraine headache, related to the presence of allodynia.

Pathophysiological targets for non-pharmacological treatment of migraine

Background Migraine is the most prevalent neurological disorder worldwide and ranked sixth among all diseases in years lived with disability. Overall preventive anti-migraine therapies have an effect in one patient out of two at the most, many of them being endowed with disabling adverse effects. No new disease-modifying drugs have come into clinical practice since the application to migraine of topiramate and botulinum toxin, the latter for its chronic form. There is thus clearly a need for more effective treatments that are devoid of, or have acceptable side effects. In recent years, scientific progress in migraine research has led to substantial changes in our understanding of the pathophysiology of migraine and paved the way for novel non-drug pathophysiological-targeted treatment strategies. Overview Several such non-drug therapies have been tested in migraine, such as oxidative phosphorylation enhancers, diets and non-invasive central or peripheral neurostimulation. All of them are promising for preventive migraine treatment and are quasi-devoid of side effects. Their advantage is that they can in theory be selected for individual patients according to their pathophysiological profile and they can (and probably should) be combined with the classical pharmacological armamentarium. Conclusion We will review here how knowledge of the functional anatomy and physiology of migraine mechanisms holds the key for more specific and effective non-pharmacological treatments.

Laboratory tests of headache disorders – dawn of a new era?

Context

The classification of headache disorders has improved over the years, but further work is needed to develop and improve headache diagnosis within headache subtypes. The present review is a call for action to implement laboratory tests in the classification and management of primary and some secondary headaches.

Background

In this narrative review we present and discuss published tests that might be useful in phenotyping and/or diagnosis of long-lasting headache disorders such as migraine, tension-type headache, trigeminal autonomic cephalalgias, trigeminal neuralgia and persisting secondary headaches.

Aim

The palpometer test, quantitative sensory testing, nociceptive blink reflex and autonomic tests may be valuable to phenotype and/or diagnose subforms of migraine, tension-type headache, cluster headache, trigeminal neuralgia and medication-overuse headache. Provocation tests with glyceryl trinitrate (GTN) and calcitonin gene-related peptide (CGRP) may be valuable in subclassification of migraine and cluster headache. Lumbar pressure monitoring and optical coherence tomography may valuable tools to diagnose and follow patients with chronic headache and raised intracranial pressure.

Finding

A number of laboratory tests in headache research are presently available, but have primarily been performed in single research studies or a few studies that differ in methods and patient groups. At present, there is no evidence-based strategy for implementing diagnostic tests, but this could be achieved if well-reputed tertiary headache centers commence developing and implementing laboratory tests in order to improve the classification and treatment of headache patients.

The Vestibulo-Collic Reflex is Abnormal in Migraine

Interictal evoked central nervous system responses are characterized in migraineurs by a deficit of habituation, at both cortical and subcortical levels. The click-evoked vestibulo-collic reflex (VCR) allows the assessment of otolith function and an oligosynaptic pathway linking receptors in the saccular macula to motoneurons of neck muscles. Three blocks of 75 averaged responses to monaural 95-dB normal hearing level 3-Hz clicks were recorded over the contracted ipsilateral sternocleidomastoid muscle in 25 migraineurs between attacks and 20 healthy subjects, without vestibular symptoms. Amplitudes, raw and corrected for baseline electromyography, were significantly smaller in migraine patients. Whereas in healthy volunteers the VCR habituated during stimulus repetition (-4.96% ± 14.3), potentiation was found in migraineurs (4.34% ± 15.3; P = 0.04). The combination with a reduced mean amplitude does not favour vestibular hyperexcitability as an explanation for the habituation deficit in migraine, but rather an abnormal processing of repeated stimuli in the reflex circuit.

The Role of the Trigemino Cervical Complex in Chronic Whiplash Associated Headache: A Cross Sectional Study

OBJECTIVE

To investigate signs of central sensitization in a cohort of patients with chronic whiplash associated headache (CWAH).

BACKGROUND

Central sensitization is one of the mechanisms leading to chronicity of primary headache, and thus might contribute to CWAH. However, the pathophysiological mechanism of CWAH is poorly understood and whether it is simply an expression of the primary headache or has a distinct pathogenesis remains unclear. Thus, the factors involved in the genesis of CWAH require further investigation.

METHODS

Twenty-two patients with CWAH (20 females, 2 males; age 25-50 years, mean age 36.3 years) and 25 asymptomatic participants (13 females, 12 males; age 18-50 years, mean age 35.6 years) rated glare and light-induced discomfort in response to light from an ophthalmoscope. Hyperalgesia evoked by a pressure algometer was assessed bilaterally on the forehead, temples, occipital base, and the middle phalanx of the third finger. The number, latency, area under the curve, and recovery cycle of nociceptive blink reflexes elicited by a supraorbital electrical stimulus were also recorded.

RESULTS

Eight and 6 CWAH patients had migrainous and tension-type headache (TTH) profiles, respectively; the remainder had features attributable to both migraine and TTH. Patients in the whiplash group reported significantly greater light-induced pain than controls (8.48 ± .35 vs 6.66 ± .43 on a 0-10 scale; P = .001). The CWAH patients reported significantly lower pressure pain thresholds at all sites. For stimuli delivered at 20 second intervals, whiplash patients were more responsive than controls (4.8 ± .6 blinks vs 3.0 ± .6 blinks in a block of 10 stimuli; P = .036). While R2 latencies and the area under the curve for the 20 second interval trials were comparable in both groups, there was a significant reduction of the area under the curve from the first to the second of the 2-second interval trials only in controls (99 ± 8% of baseline in whiplash patients vs 68 ± 7% in controls; P = .009). The recovery cycle was comparable for both groups.

CONCLUSIONS

Our results corroborate previous findings of mechanical hypersensitivity and photophobia in CWAH patients. The neurophysiological data provide further evidence for hyperexcitability in central nociceptive pathways, and endorse the hypothesis that CWAH may be driven by central sensitization.

Differences in central facilitation between episodic and chronic migraineurs in nociceptive-specific trigeminal pathways

Background

The trigeminal nociceptive system plays a pivotal role in the pathophysiology of migraines. The present study investigated whether there are differences between patients with episodic migraine (EM) and patients with chronic migraine (CM) in trigeminal pain processing at the brainstem and cortical levels using the nociceptive blink reflex (nBR) and pain-related evoked potentials (PREP).

Methods

This study assessed 68 female migraineurs (38 EM patients and 30 CM patients) and 40 age-matched controls using simultaneous recordings of nBR and PREP during the interictal period.

Results

In terms of the nBR, EM patients displayed significantly decreased latencies and larger amplitudes and area-under-the-curve (AUC) values for the R2 component, whereas CM patients showed significantly prolonged latencies and smaller amplitudes and AUC values for the R2 component (p < 0.05). In terms of PREP, both the EM and CM patients had decreased latencies (N1, P1), with larger amplitude compared with the controls (p < 0.05), which indicates facilitation at the cortical level. Additionally, the amplitude and AUC values of the R2 component exhibited a negative correlation, whereas the latency of the R2 component for the nBR showed a positive correlation, with the frequency of headaches in migraineurs (p < 0.01).

Conclusions

In the present study, the facilitation in the trigeminal nociceptive pathway of the EM group suggests the occurrence of migraine-specific hyperexcitability. Additionally, the suppression of R2 at the brainstem level in the CM group may relate to impaired or dysfunctional descending pain modulation. These findings suggest that there are adaptive or maladaptive responses due to the chronification of migraine attacks.

Therapeutic antibodies against CGRP or its receptor

CGRP is an extensively studied neuropeptide that has been implicated in the pathophysiology of migraine. While a number of small molecule antagonists against the CGRP receptor have demonstrated that targeting this pathway is a valid and effective way of treating migraine, off-target hepatoxicity and formulation issues have hampered the development for regulatory approval of any therapeutic in this class. The development of monoclonal antibodies to CGRP or its receptor as therapeutic agents has allowed this pathway to be re-investigated. Herein we review why CGRP is an ideal target for the prevention of migraine and describe four monoclonal antibodies against either CGRP or its receptor that are in clinical development for the treatment of both episodic and chronic migraine. We describe what has been publically disclosed about their clinical trials and future clinical development plans.

Persistent Postural-Perceptual Dizziness: A Matter of Higher, Central Dysfunction?

Objective

Persistent postural-perceptual dizziness (PPPD) is the most common vestibular disorder in the age group between 30 and 50 years. It is considered to be based on a multisensory maladjustment involving alterations of sensory response pattern including vestibular, visual and motion stimuli. Previous data supported a link between vestibular and pain mechanism. The aim of the study was to investigate whether other sensory inputs such as pain stimuli might be altered in terms of a more widespread central perception dysfunction in this disorder.

Methods

Nociceptive blink reflex was measured in 27 patients with PPPD and compared with 27 healthy, age and gender matched controls. The habituation of the R2 component of the blink reflex was evaluated as the percentage area-under-the curve (AUC) decrease in ten consecutive blocks of five averaged rectified responses. Additionally, clinical characteristics were evaluated.

Results

In patients with PPPD a lack of habituation was observed compared to healthy controls. Relative AUC decreased between the first and the tenth block by 19.48% in PPPD patients and by 31.63% (p = 0.035) in healthy controls. There was no correlation between clinical data (course of disease, comorbid depression, medication, trigger factors) or electrophysiological data (perception threshold, pain threshold, stimulus intensity) and habituation pattern. No trigeminal sensitization in terms of facilitation of absolute values could be detected.

Conclusion

Our study results supports the hypothesis of the multisensory dimension of impaired sensory processing in patients with PPPD extends beyond vestibular/visual motion stimuli and reflexive postural/oculomotor control mechanisms to other sensory inputs such as pain perception in terms of a more generalized disturbed habituation pattern.

Nociception-specific blink reflex: pharmacology in healthy volunteers

BACKGROUND

The physiology and pharmacology of activation or perception of activation of pain-coding trigeminovascular afferents in humans is fundamental to understanding the biology of headache and developing new treatments.

METHODS

The blink reflex was elicited using a concentric electrode and recorded in four separate sessions, at baseline and two minutes after administration of ramped doses of diazepam (final dose 0.07 mg/kg), fentanyl (final dose 1.11 μg/kg), ketamine (final dose 0.084 mg/kg) and 0.9 % saline solution. The AUC (area under the curve, μV*ms) and the latency (ms) of the ipsi- and contralateral R2 component of the blink reflex were calculated by PC-based offline analysis. Immediately after each block of blink reflex recordings certain psychometric parameters were assessed.

RESULTS

There was an effect due to DRUG on the ipsilateral (F 3,60 = 7.3, P < 0.001) AUC as well as on the contralateral (F 3,60 = 6.02, P < 0.001) AUC across the study. A significant decrement in comparison to placebo was observed only for diazepam, affecting the ipsilateral AUC. The scores of alertness, calmness, contentedness, reaction time and precision were not affected by the DRUG across the sessions.

CONCLUSION

Previous studies suggest central, rather than peripheral changes in nociceptive trigeminal transmission in migraine. This study demonstrates a robust effect of benzodiazepine receptor modulation of the nociception specific blink reflex (nBR) without any μ-opiate or glutamate NMDA receptor component. The nociception specific blink reflex offers a reproducible, quantifiable method of assessment of trigeminal nociceptive system in humans that can be used to dissect pharmacology relevant to primary headache disorders.

Laser-evoked potential habituation and central sensitization symptoms in childhood migraine

Objectives

Few studies have addressed central sensitization symptoms and pain processing in childhood migraine. Our aims were to examine pain sensitivity and responses, including habituation, evoked by CO2 laser stimuli (laser-evoked potentials (LEPs)) in a cohort of children with migraine compared to non-migraine controls and to determine the correlation between LEP features and signs of central sensitization.

Methods

Thirty-five patients 8–15 years of age with migraines without aura were evaluated during the inter-critical phase and were compared to 17 controls. LEPs were analyzed, and their main features were correlated with clinical symptoms including allodynia and pericranial tenderness.

Results

The laser-evoked pain threshold was lower and the N2P2 vertex complex amplitude was higher in children with migraines. Furthermore, habituation of vertex waves of LEPs clearly showed a tendency toward progressive amplitude enhancement in the migraine group. Acute allodynia and inter-critical pericranial tenderness correlated with trigeminal LEP features, particularly with the abnormal habituation pattern.

Discussion

Abnormalities of pain processing and symptoms of central sensitization appear to be characteristics of children with migraine. Reduced habituation and progressive amplification of cortical responses to laser stimuli indicate an overactive nociceptive system at the onset of migraine, and this hyperactivity may subtend allodynia and pericranial tenderness. Future prospective trials may aid in the early identification of clinical phenotypes that display a tendency to develop into the chronic form of migraine, warranting a timely therapeutic approach.

Lateralized nociceptive blink reflex habituation deficit in episodic cluster headache: Correlations with clinical features

BACKGROUND

We previously observed impaired habituation mechanisms of the conventional blink reflex (BR) in patients with episodic cluster headache (ECH) during the bout, studying only the affected side. Here, we have studied the nociceptive-specific BR (nBR) both on the affected and non-affected sides, and in relation to clinical features.

PARTICIPANTS AND METHODS

We recorded nBR in 18 ECH patients during the bout, and in 18 healthy volunteers (HVs). We compared pain threshold, area, and habituation of the nBR, recorded both for the affected and non-affected sides.

RESULTS

In patients, the pain threshold on the affected side was lower than that of the non-affected side (p = 0.009), and lower than in HVs (p = 0.038). Reflex area was decreased on both sides (p < 0.05) compared with HVs, whereas habituation was significantly impaired only on the affected side (p = 0.025 vs. HVs; p = 0.003 vs. non-affected). The habituation slope was positively correlated with the number of days since the onset of the bout and the daily attack frequency.

CONCLUSIONS

Our data reflect lateralized pathological variations in craniofacial nociception in ECH patients over the course of the cluster period. We hypothesized that this is due to malfunctioning of mechanisms that regulate hypothalamic activity and descending aminergic controls.

Effects of visual cortex activation on the nociceptive blink reflex in healthy subjects

Bright light can cause excessive visual discomfort, referred to as photophobia. The precise mechanisms linking luminance to the trigeminal nociceptive system supposed to mediate this discomfort are not known. To address this issue in healthy human subjects we modulated differentially visual cortex activity by repetitive transcranial magnetic stimulation (rTMS) or flash light stimulation, and studied the effect on supraorbital pain thresholds and the nociceptive-specific blink reflex (nBR). Low frequency rTMS that inhibits the underlying cortex, significantly decreased pain thresholds, increased the 1st nBR block ipsi- and contralaterally and potentiated habituation contralaterally. After high frequency or sham rTMS over the visual cortex, and rMS over the right greater occipital nerve we found no significant change. By contrast, excitatory flash light stimulation increased pain thresholds, decreased the 1st nBR block of ipsi- and contralaterally and increased habituation contralaterally. Our data demonstrate in healthy subjects a functional relation between the visual cortex and the trigeminal nociceptive system, as assessed by the nociceptive blink reflex. The results argue in favour of a top-down inhibitory pathway from the visual areas to trigemino-cervical nociceptors. We postulate that in normal conditions this visuo-trigeminal inhibitory pathway may avoid disturbance of vision by too frequent blinking and that hypoactivity of the visual cortex for pathological reasons may promote headache and photophobia.

The blink reflex test does not show abnormalities in a large group of patients with chronic migraine

The blink reflex - a simple, non-invasive and inexpensive test - may be indicative of lesions or dysfunctions of the brainstem, and particularly assesses the trigeminal-facial arch. Results from alterations of the blink reflex in patients with headaches have provided controversial data.

METHOD

Registration of the waves R1 and R2 (ipsilateral to the stimulus) and R2c (contralateral to the stimulus) by electroneuromyography.

RESULTS

A large number of controls (n=160) and patients with chronic migraine (n=160) were studied. No significant differences were observed between the two groups.

CONCLUSION

It is possible that this relatively simple and primitive reflex is not affected unless there is significant damage to the brainstem.

Pathophysiology of hypnic headache

Background

Hypnic headache (HH) is a rare primary headache disorder that is characterized by strictly sleep related headache attacks.

Purpose

The underlying pathophysiology of HH is mainly enigmatic but some clinical characteristics such as circadian rhythmicity and caffeine responsiveness may point toward possible underlying mechanisms.

Method

Current studies that deal with the pathophysiology of HH are summarized. Data on cerebral imaging, sleep, electrophysiology studies, effectiveness of drugs, and symptomatic headache types are discussed to illuminate underlying pathophysiologic mechanisms.

Conclusion

HH can be clearly differentiated by its clinical presentation as well as imaging and electrophysiological study results from other primary headaches such as migraine or cluster headache. The underlying pathophysiology is still enigmatic but a hypothalamic involvement seems to be likely.

Is the migrainous brain normal outside of acute attacks? Lessons learned from psychophysical, neurochemical and functional neuroimaging studies

Migraine is a largely inherited disorder of the brain with recurrent head pain attacks. There is an increasing awareness, however, that the manifestation of migrainous biology is not restricted to such acute head pain attacks, but that migraine is rather a disorder with a continuous complex and broad sensory processing dysfunction in which normal sensory stimuli (somatosensory, visual, auditory and olfactory) are misinterpreted by the brain. This dysfunction is most prominent during attacks, but there are more and more evidences that the processing and perception of stimuli is abnormal also outside of attacks to a varying degree. In this topical review, we will summarize and discuss the current clinical, neurochemical and functional neuroimaging literature on this paradigm shift from a strictly episodic head pain disorder to migraine as a more general dysfunction of sensory processing.

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.

Pearls and pitfalls: electrophysiology for primary headaches

BACKGROUND

Primary headaches are functional neurological diseases characterized by a dynamic cyclic pattern over time (ictal/pre-/interictal). Electrophysiological recordings can non-invasively assess the activity of an underlying nervous structure or measure its response to various stimuli, and are therefore particularly appropriate for the study of primary headaches. Their interest, however, is chiefly pathophysiological, as interindividual, and to some extent intraindividual, variations preclude their use as diagnostic tools.

AIM OF THE WORK

This article will review the most important findings of electrophysiological studies in primary headache pathophysiology, especially migraine on which numerous studies have been published.

RESULTS

In migraine, the most reproducible hallmark is the interictal lack of neuronal habituation to the repetition of various types of sensory stimulations. The mechanism subtending this phenomenon remains uncertain, but it could be the consequence of a thalamocortical dysrythmia that results in a reduced cortical preactivation level. In tension-type headache as well as in cluster headache, there seems to be an impairment of central pain-controlling mechanisms but the studies are scarce and their outcomes are contradictory. The discrepancies between studies might be as a result of methodological differences as well as patients' dissimilarities, which are also discussed.

CONCLUSIONS AND PERSPECTIVES

Electrophysiology is complementary to functional neuroimaging and will undoubtedly remain an important tool in headache research. One of its upcoming applications is to help select neurostimulation techniques and protocols that correct best the functional abnormalities detectable in certain headache disorders.

Asynchronicity of facial blood perfusion in migraine

Asymmetrical changes in blood perfusion and asynchronous blood supply to head tissues likely contribute to migraine pathophysiology. Imaging was widely used in order to understand hemodynamic variations in migraine. However, mapping of blood pulsations in the face of migraineurs has not been performed so far. We used the Blood Pulsation Imaging (BPI) technique, which was recently developed in our group, to establish whether 2D-imaging of blood pulsations parameters can reveal new biomarkers of migraine. BPI characteristics were measured in migraineurs during the attack-free interval and compared to healthy subjects with and without a family history of migraine. We found a novel phenomenon of transverse waves of facial blood perfusion in migraineurs in contrast to healthy subjects who showed synchronous blood delivery to both sides of the face. Moreover, the amplitude of blood pulsations was symmetrically distributed over the face of healthy subjects, but asymmetrically in migraineurs and subjects with a family history of migraine. In the migraine patients we found a remarkable correlation between the side of unilateral headache and the direction of the blood perfusion wave. Our data suggest that migraine is associated with lateralization of blood perfusion and asynchronous blood pulsations in the facial area, which could be due to essential dysfunction of the autonomic vascular control in the face. These findings may further enhance our understanding of migraine pathophysiology and suggest new easily available biomarkers of this pathology.

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.