Intracortical Inhibition and Facilitation in Migraine-A Transcranial Magnetic Stimulation Study

Efficacy of a dual task protocol on neurophysiological and clinical outcomes in migraine: a randomized control trial

The main aim of this study was to investigate the efficacy of a dual task protocol in people with episodic migraine with respect to both active exercises only and cognitive task only treatments, concerning some neurophysiological and clinical outcomes. A randomized control trial was adopted in people with episodic migraine without aura. Some neurophysiological and clinical outcomes were collected (t0): resting motor threshold (rMT), short intracortical inhibition (SICI) and facilitation (ICF), pressure pain threshold (PPT), trail making test (TMT), frontal assessment battery (FAB), headache-related disability (MIDAS) and headache parameters. Then, participants were randomized into three groups: active exercise only (n = 10), cognitive task only (n = 10) and dual task protocol (n = 10). After 3 months of each treatment and after 1-month follow-up the same neurophysiological and clinical outcomes were revaluated. A significant time x group effect was only found for the trapezius muscle (p = 0.012, pη2 = 0.210), suggesting that PPT increased significantly only in active exercise and dual task protocol groups. A significant time effect was found for rMT (p < 0.001, pη2 = 0.473), MIDAS (p < 0.001, pη2 = 0.426), TMT (p < 0.001, pη2 = 0.338) and FAB (p < 0.001, pη2 = 0.462). A repeated measures ANOVA for SICI at 3 ms highlighted a statistically significant time effect for the dual task group (p < 0.001, pη2 = 0.629), but not for the active exercises group (p = 0.565, pη2 = 0.061), and for the cognitive training (p = 0.357, pη2 = 0.108). The dual task protocol seems to have a more evident effect on both habituation and sensitization outcomes than the two monotherapies taken alone in people with migraine.

Effects of Anti-CGRP Monoclonal Antibodies on Neurophysiological and Clinical Outcomes: A Combined Transcranial Magnetic Stimulation and Algometer Study

BACKGROUND

the aim of this study was to investigate the neurophysiological effect of anti-CGRP monoclonal antibodies on central and peripheral levels in migraine patients.

METHODS

An observational cohort study in patients with migraine was performed. All subjects underwent Single-Pulse and Paired-Pulse Transcranial Magnetic Stimulation, as well as a Pressure Pain Threshold assessment. The same protocol was repeated three and four months after the first injection of anti-CGRP monoclonal antibodies.

RESULTS

A total of 11 patients with a diagnosis of migraine and 11 healthy controls were enrolled. The main findings of this study are the significant effects of anti-CGRP mAb treatment on the TMS parameters of intracortical inhibition and the rise in the resting motor threshold in our group of patients affected by resistant migraine. The clinical effect of therapy on migraine is associated with the increase in short-interval intracortical inhibition (SICI), resting motor threshold (RMT), and Pressure Pain Threshold (PPT). In all patients, all clinical headache parameters improved significantly 3 months after the first injection of mAbs and the improvement was maintained at the 1-month follow-up. At baseline, migraineurs and HCs had significant differences in all TMS parameters and in PPT, while at follow-up assessment, no differences were observed on RMT, SICI, and PPT between the two groups. After anti-CGRP monoclonal antibody injection, a significant increase in the intracortical inhibition, in the motor threshold, and in the Pressure Pain Threshold in critical head areas was observed in patients with migraine, which was related to significant clinical benefits.

CONCLUSIONS

Anti-CGRP monoclonal antibodies improved clinical and neurophysiological outcomes, reflecting a normalization of cortical excitability and peripheral and central sensitization. By directly acting on the thalamus or hypothalamus and indirectly on the trigeminocervical complex, treatment with anti-CGRP monoclonal antibodies may modulate central sensorimotor excitability and peripheral sensitization pain.

Effects of pain on cortical homeostatic plasticity in humans: a systematic review

Homeostatic plasticity (HP) is a negative feedback mechanism that prevents excessive facilitation or depression of cortical excitability (CE). Cortical HP responses in humans have been investigated by using 2 blocks of noninvasive brain stimulation with a no-stimulation block in between. A healthy HP response is characterized by reduced CE after 2 excitatory stimulation blocks and increased CE when using inhibitory stimulation. Conversely, impaired HP responses have been demonstrated in experimental and chronic pain conditions. Therefore, this systematic review aimed to provide an overview of the effect of pain on cortical HP in humans. Scopus, Embase, and PubMed were searched from inception until November 20, 2023. The included studies (1) compared experimental or clinical pain conditions with healthy controls, (2) induced HP using 2 blocks of stimulation with a no-stimulation interval, and (3) evaluated CE measures such as motor-evoked potentials. Four studies were included, consisting of 5 experiments and 146 participants, of whom 63 were patients with chronic pain and 48 were subjected to an experimental pain model. This systematic review found support for an HP impairment in pain compared with that in pain-free states, reflected by a lack of CE reduction after excitatory-excitatory HP induction over the primary motor cortex. Inhibitory-inhibitory HP induction did not produce a consistent HP response across studies, independent of pain or pain-free states. Standardization of HP induction protocols and outcome calculations is needed to ensure reproducibility and study comparison. Future HP studies may consider investigating sensory domains including nociception, which would further our understanding of abnormal HP regulation in pain conditions.

Females with painful temporomandibular disorders present higher intracortical facilitation relative to pain-free controls

OBJECTIVES

This study aimed to investigate cortical excitability differences in the primary motor cortex (M1) hand representation between individuals with temporomandibular disorders (TMD) and healthy controls. We assessed resting motor thresholds, motor-evoked potentials (MEPs), intracortical inhibition, and intracortical facilitation and explored potential associations with clinical and psychosocial characteristics in the TMD group.

MATERIALS AND METHODS

We recruited 36 female participants with TMD and 17 pain-free controls. Transcranial magnetic stimulation (TMS) was used to assess M1 cortical excitability. Correlations between clinical and psychosocial factors and cortical excitability measures were also evaluated.

RESULTS

Patients with TMD showed significantly higher intracortical facilitation at 12 ms (z = 1.98, p = 0.048) and 15 ms (z = 2.65, p = 0.008) when compared to controls. Correlations revealed associations between intracortical facilitation and pain interference, sleep quality, depressive symptoms, and pain catastrophizing in the TMD group.

CONCLUSIONS

Females with TMD exhibit heightened motor cortex intracortical facilitation in the hand representation, potentially indicating altered cortical excitability beyond the motor face area. This suggests a role for cortical excitability in TMD pathophysiology, influenced by psychosocial factors.

CLINICAL RELEVANCE

Understanding cortical excitability in TMD may inform targeted interventions. Psychosocial variables may play a role in cortical excitability, emphasizing the multidimensional nature of TMD-related pain. Further research is needed to confirm and expand upon these findings, with potential implications for the management of TMD and related pain conditions.

Electrophysiological findings in migraine may reflect abnormal synaptic plasticity mechanisms: A narrative review

BACKGROUND

The cyclical brain disorder of sensory processing accompanying migraine phases lacks an explanatory unified theory.

METHODS

We searched Pubmed for non-invasive neurophysiological studies on migraine and related conditions using transcranial magnetic stimulation, electroencephalography, visual and somatosensory evoked potentials. We summarized the literature, reviewed methods, and proposed a unified theory for the pathophysiology of electrophysiological abnormalities underlying migraine recurrence.

RESULTS

All electrophysiological modalities have determined specific changes in brain dynamics across the different phases of the migraine cycle. Transcranial magnetic stimulation studies show unbalanced recruitment of inhibitory and excitatory circuits, more consistently in aura, which ultimately results in a substantially distorted response to neuromodulation protocols. Electroencephalography investigations highlight a steady pattern of reduced alpha and increased slow rhythms, largely located in posterior brain regions, which tends to normalize closer to the attacks. Finally, non-painful evoked potentials suggest dysfunctions in habituation mechanisms of sensory cortices that revert during ictal phases.

CONCLUSION

Electrophysiology shows dynamic and recurrent functional alterations within the brainstem-thalamus-cortex loop varies continuously and recurrently in migraineurs. Given the central role of these structures in the selection, elaboration, and learning of sensory information, these functional alterations suggest chronic, probably genetically determined dysfunctions of the synaptic short- and long-term learning mechanisms.

Prolonged continuous theta burst stimulation increases motor corticospinal excitability and intracortical inhibition in patients with neuropathic pain: An exploratory, single-blinded, randomized controlled trial

OBJECTIVES

A new paradigm for Transcranial Magnetic Stimulation (TMS), referred to as prolonged continuous theta burst stimulation (pcTBS), has recently received attention in the literature because of its advantages over high frequency repetitive TMS (HF-rTMS). Clinical advantages include less time per intervention session and the effects appear to be more robust and reproducible than HF-rTMS to modulate cortical excitability. HF-rTMS targeted at the primary motor cortex (M1) has demonstrated analgesic effects in patients with neuropathic pain but their mechanisms of action are unclear and pcTBS has been studied in healthy subjects only. This study examined the neural mechanisms that have been proposed to play a role in explaining the effects of pcTBS targeted at the M1 and DLPFC brain regions in neuropathic pain (NP) patients with Type 2 diabetes.

METHODS

Forty-two patients with painful diabetic neuropathy were randomized to receive a single session of pcTBS targeted at the left M1 or left DLPFC. pcTBS stimulation consisted of 1,200 pulses delivered in 1 min and 44 s with a 35-45 min gap between sham and active pcTBS stimulation. Both the activity of the descending pain system which was examined using conditioned pain modulation and the activity of the ascending pain system which was assessed using temporal summation of pain were recorded using a handheld pressure algometer by measuring pressure pain thresholds. The amplitude of the motor evoked potential (MEP) was used to measure motor corticospinal excitability and GABA activity was assessed using short (SICI) and long intracortical inhibition (LICI). All these measurements were performed at baseline and post-pcTBS stimulation.

RESULTS

Following a single session of pcTBS targeted at M1 and DLPFC, there was no change in BPI-DN scores and on the activity of the descending (measured using conditioned pain modulation) and ascending pain systems (measured using temporal summation of pain) compared to baseline but there was a significant improvement of >13% in perception of acute pain intensity, increased motor corticospinal excitability (measured using MEP amplitude) and intracortical inhibition (measured using SICI and LICI).

CONCLUSION

In patients with NP, a single session of pcTBS targeted at the M1 and DLPFC modulated the neurophysiological mechanisms related to motor corticospinal excitability and neurochemical mechanisms linked to GABA activity, but it did not modulate the activity of the ascending and descending endogenous modulatory systems. In addition, although BPI-DN scores did not change, there was a 13% improvement in self-reported perception of acute pain intensity.

Clinical diagnostic utility of transcranial magnetic stimulation in neurological disorders. Updated report of an IFCN committee

The review provides a comprehensive update (previous report: Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, et al. The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee. Clin Neurophysiol 2008;119(3):504-32) on clinical diagnostic utility of transcranial magnetic stimulation (TMS) in neurological diseases. Most TMS measures rely on stimulation of motor cortex and recording of motor evoked potentials. Paired-pulse TMS techniques, incorporating conventional amplitude-based and threshold tracking, have established clinical utility in neurodegenerative, movement, episodic (epilepsy, migraines), chronic pain and functional diseases. Cortical hyperexcitability has emerged as a diagnostic aid in amyotrophic lateral sclerosis. Single-pulse TMS measures are of utility in stroke, and myelopathy even in the absence of radiological changes. Short-latency afferent inhibition, related to central cholinergic transmission, is reduced in Alzheimer's disease. The triple stimulation technique (TST) may enhance diagnostic utility of conventional TMS measures to detect upper motor neuron involvement. The recording of motor evoked potentials can be used to perform functional mapping of the motor cortex or in preoperative assessment of eloquent brain regions before surgical resection of brain tumors. TMS exhibits utility in assessing lumbosacral/cervical nerve root function, especially in demyelinating neuropathies, and may be of utility in localizing the site of facial nerve palsies. TMS measures also have high sensitivity in detecting subclinical corticospinal lesions in multiple sclerosis. Abnormalities in central motor conduction time or TST correlate with motor impairment and disability in MS. Cerebellar stimulation may detect lesions in the cerebellum or cerebello-dentato-thalamo-motor cortical pathways. Combining TMS with electroencephalography, provides a novel method to measure parameters altered in neurological disorders, including cortical excitability, effective connectivity, and response complexity.

Understanding intracortical excitability in phantom limb pain: A multivariate analysis from a multicenter randomized clinical trial

OBJECTIVES

To explore associations of intracortical excitability with clinical characteristics in a large sample of subjects with phantom limb pain (PLP).

METHODS

Ancillary study using baseline and longitudinal data from a large multicenter randomized trial that investigated the effects of non-invasive brain stimulation combined with sensorimotor training on PLP. Multivariate regression modeling analyses were used to investigate the association of intracortical excitability, measured by percentages of intracortical inhibition (ICI) and facilitation (ICF) with clinical variables.

RESULTS

Ninety-eight subjects were included. Phantom sensation of itching was positively associated with ICI changes and at baseline in the affected hemisphere (contralateral to PLP). However, in the non-affected hemisphere (ipsilateral to PLP), the phantom sensation of warmth and PLP intensity were negatively associated with ICI (both models). For the ICF, PLP intensity (baseline model only) and age (longitudinal model) were negatively associated, while time since amputation and amputation level (both for longitudinal model only) were positively associated in the affected hemisphere. Additionally, use of antidepressants led to lower ICF in the non-affected hemisphere for the baseline model while higher amputation level also led to less changes in the ICF.

CONCLUSION

Results revealed clear associations of clinical variables and cortical excitability in a large chronic pain sample. ICI and ICF changes appear not to be mainly explained by PLP intensity. Instead, other variables associated with duration of neuroplasticity changes (such as age and duration of amputation) and compensatory mechanisms (such as itching and phantom limb sensation) seem to be more important in explaining these variables.

A Systematic Review of Long-Interval Intracortical Inhibition as a Biomarker in Neuropsychiatric Disorders

Long-interval intracortical inhibition (LICI) is a paired-pulse transcranial magnetic stimulation (TMS) paradigm mediated in part by gamma-aminobutyric acid receptor B (GABA_B) inhibition. Prior work has examined LICI as a putative biomarker in an array of neuropsychiatric disorders. This review conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) sought to examine existing literature focused on LICI as a biomarker in neuropsychiatric disorders. There were 113 articles that met the inclusion criteria. Existing literature suggests that LICI may have utility as a biomarker of GABA_B functioning but more research with increased methodologic rigor is needed. The extant LICI literature has heterogenous methodology and inconsistencies in findings. Existing findings to date are also non-specific to disease. Future research should carefully consider existing methodological weaknesses and implement high-quality test-retest reliability studies.

Intracortical facilitation within the migraine motor cortex depends on the stimulation intensity. A paired-pulse TMS study

Introduction

Connectivity within the primary motor cortex can be measured using the paired-pulse transcranial magnetic stimulation (TMS) paradigm. This evaluates the effect of a first conditioning stimulus on the motor evoked potential (MEP) elicited by a second test stimulus when different interstimulus intervals are used. Aim of the present study was to provide, in patients suffering from migraine without aura (MwoA), additional information on intracortical facilitation (ICF), short intracortical inhibition (SICI), and long intracortical inhibition (LICI), using different intensities of the test stimulus (TS).

Methods

We enrolled 24 patients with episodic MwoA and 24 age- and sex-matched healthy volunteers. Both patients and controls were randomly assigned to two different experimental groups: the first group underwent evaluation of ICF, while in the second group we assessed SICI and LICI. All these measures were assessed by using three different suprathreshold intensities of the TS (110%, 130% and 150% of the resting motor threshold, RMT). Interstimulus intervals (ISIs) of 10 ms were used for testing ICF, while SICI and LICI were carried out by using 2 ms and 100 ms ISIs respectively. All migraine patients underwent the experimental protocol while in the interictal pain-free state.

Results

A main finding of the study was that an increased ICF could be seen in migraineurs as compared to the healthy subjects only by using a 110% intensity of the TS. Instead, no significant differences were observed between patients and controls as regards both measures of intracortical inhibition.

Conclusion

We show that hyperresponsivity of the glutamatergic intracortical circuits can be detected in the migraine motor cortex only by applying a low suprathreshold intensity of stimulation. Our results strengthen the notion that, to be reliable, the assessment of cortical excitability in migraine should always include evaluation of the cortical response to different stimulation intensities.

The Association Between Corticomotor Excitability and Motor Skill Learning in People With Painful Hand Arthritis

OBJECTIVES

Previous studies have shown a tendency for reduced motor cortex inhibition in chronic pain populations. People with chronic pain also routinely demonstrate motor deficiencies, including skill learning. The goals of the current study were to (1) provide a thorough analysis of corticomotor and intracortical excitability in people with chronic arthritic hand pain, and (2) examine the relationship between these measures and performance on a motor skill learning task.

METHODS

Twenty-three people with arthritic hand pain and 20 pain-free controls participated in a cross-sectional study. Transcranial magnetic stimulation was used to assess corticomotor and intracortical excitability of the first dorsal interosseus muscle. Participants then completed a 30-minute motor skill training task involving the index finger of the same hand.

RESULTS

Hand arthritis participants showed evidence of reduced intracortical inhibition and enhanced facilitation, which correlated with duration of hand pain. Arthritis participants were initially poorer at the motor skill task but over the total training time performance was equivalent between groups. There were no associations found between measures of intracortical excitability and motor skill learning.

DISCUSSION

Our findings are the first to provide evidence of cortical disinhibition in people with painful arthritis, as previously demonstrated in other chronic pain populations. Cortical excitability changes may progress the longer pain persists, with increased pain duration being associated with greater cortical disinhibition. There was no evidence that these changes in cortical excitability are related to impaired motor function or skill learning.

Corticospinal excitability as a biomarker of myofascial pain syndrome

INTRODUCTION

Myofascial pain syndrome (MPS) is a common chronic pain disorder that lacks effective diagnostic criteria. To better understand neurophysiological changes in chronic pain, several trials exploring corticospinal excitability in different populations of patients with chronic pain have been performed.

OBJECTIVES

In this systematic review, we aimed to investigate the current literature on MPS and intracortical disinhibition, by means of increased intracortical facilitation and decreased intracortical inhibition (ICI).

METHODS

We performed a search on PubMed to identify clinical trials on MPS and transcranial magnetic stimulation measurements. We then applied the Harford Hill criteria to the identified studies to assess the possible causal relationship between intracortical disinhibition measurements and MPS. Finally, we compared our findings on MPS with other chronic pain conditions.

RESULTS

Four studies assessing corticospinal excitability in patients with MPS were found. Although the amount of trials available is limited, all the reported studies indicated an increased intracortical disinhibition in patients with MPS. Importantly, these measurements were also correlated with psychological factors, such as pain catastrophism, or anxiety. However, based on the Harford Hill criteria, we could not assert a strong causal relationship between these markers and MPS. Although intracortical disinhibition has been consistently found in patients having MPS, this lack of cortical inhibition was not only observed in this specific chronic pain syndrome but also in fibromyalgia and neuropathic pain conditions.

CONCLUSION

Intracortical disinhibition seems to be a marker that has been consistently observed in MPS. Future prospective cohort studies could provide new insights in the development of neoplastic and maladaptive changes occurring in chronic pain syndromes and help the development of new therapeutic options.

Reduced threshold for inhibitory homeostatic responses in migraine motor cortex? A tDCS/TMS study

BACKGROUND AND OBJECTIVE

Neurophysiological studies in migraine have reported conflicting findings of either cortical hyper- or hypoexcitability. In migraine with aura (MwA) patients, we recently documented an inhibitory response to suprathreshold, high-frequency repetitive transcranial magnetic stimulation (hf-rTMS) trains applied to the primary motor cortex, which is in contrast with the facilitatory response observed in the healthy subjects. The aim of the present study was to support the hypothesis that in migraine, because of a condition of basal increased cortical responsivity, inhibitory homeostatic like mechanisms of cortical excitability could be induced by high magnitude stimulation. For this purpose, the hf-rTMS trains were preconditioned by transcranial direct current stimulation (tDCS), a noninvasive brain stimulation technique able to modulate the cortical excitability state.

METHODS

Twenty-two MwA patients and 20 patients with migraine without aura (MwoA) underwent trains of 5-Hz repetitive transcranial magnetic stimulation at an intensity of 130% of the resting motor threshold, both at baseline and after conditioning by 15 minutes of cathodal or anodal tDCS. Motor cortical responses to the hf-rTMS trains were compared with those of 14 healthy subjects.

RESULTS

We observed abnormal inhibitory responses to the hf-rTMS trains given at baseline in both MwA and MwoA patients as compared with the healthy subjects (P < .00001).The main result of the study was that cathodal tDCS, which reduces the cortical excitability level, but not anodal tDCS, which increases it, restored the normal facilitatory response to the hf-rTMS trains in both MwA and MwoA.

CONCLUSIONS

The present findings strengthen the notion that, in migraine with and without aura, the threshold for inducing inhibitory mechanisms of cortical excitability might be lower in the interictal period. This could represent a protective mechanism counteracting cortical hyperresponsivity. Our results could be helpful to explain some conflicting neurophysiological findings in migraine and to get insight into the mechanisms underlying recurrence of the migraine attacks.

Transcranial direct current stimulation in the prophylactic treatment of migraine based on interictal visual cortex excitability abnormalities: A pilot randomized controlled trial

PURPOSE

The aims of this paper are (i) to compare the excitability of visual cortex in migraine patients with healthy volunteers; and (ii) if an abnormal excitability has been found, to modulate cortical excitability in migraine patients with transcranial direct current stimulation (tDCS) and observe their clinical and neurophysiological effects.

METHODS

The study was divided into two steps. A cross-sectional study (step 1) was conducted to compare the cortical excitability of 23 migraineurs (11 with and 12 without aura) on 11 healthy individuals. On step 2, a randomized, double blinded, controlled pilot trial was carried on with 19 migraineurs, randomly divided into: experimental and control group. During 12 sessions, experimental and group received active tDCS to visual cortex and control group received sham tDCS. The headache diary was applied for a total of 90days (before, during and after tDCS sessions). Phosphene threshold (PT) induced by transcranial magnetic stimulation was recorded to measure the excitability of the visual cortex before and after each session.

RESULTS

Step 1 showed higher level of cortical excitability between migraineurs when compared to healthy volunteers; therefore, cathodal tDCS was applied over visual cortex in step 2. After tDCS application, a significant decrease was observed in a number of migraine attacks, painkiller intake and duration of each attack just in experimental group. The analysis of PT indicated no difference in cortical excitability after tDCS.

CONCLUSIONS

Findings of the study suggested that inhibitory tDCS on visual cortex might be an alternative and non-pharmacological treatment for migraine prophylaxis. However the clinical improvements of patients after tDCS treatment are not correlated with changes in cortical excitability.

Randomized Sham Controlled Double-blind Trial of Repetitive Transcranial Magnetic Stimulation for Adults With Severe Tourette Syndrome

BACKGROUND

A small proportion of individuals with Tourette syndrome (TS) have a lifelong course of illness that fails to respond to conventional treatments. Open label studies have suggested that low frequency (1-Hz) repetitive transcranial magnetic stimulation (rTMS) targeting the supplementary motor area (SMA) may be effective in reducing tic severity.

OBJECTIVE/HYPOTHESIS

To examine the efficacy of rTMS over the SMA for TS in a randomized double-blind sham-controlled trial (RCT).

METHODS

We conducted a two-site RCT-rTMS with 20 adults with severe TS for 3 weeks. Treatment consisted of 15 sessions (1-Hz; 30 min; 1800 pulses per day) of active or sham rTMS at 110% of the motor threshold over the SMA. A subsequent 3 week course of active rTMS treatment was offered.

RESULTS

Of the 20 patients (16 males; mean age of 33.7 ± 12.2 years), 9 received active and 11 received sham rTMS. After 3 weeks, patients receiving active rTMS showed on average a 17.3% reduction in the YGTSS total tic score compared to a 13.2% reduction in those receiving sham rTMS, resulting in no statistically significant reduction in tic severity (P = 0.27). An additional 3 week open label active treatment for those patients (n = 7) initially randomized to active rTMS resulted in a significant overall 29.7% reduction in tic severity compared to baseline (P = 0.04).

CONCLUSION

This RCT did not demonstrate efficacy of 3-week SMA-targeted low frequency rTMS in the treatment of severe adult TS. Further studies using longer or alternative stimulation protocols are warranted.

Brain stimulation in migraine

Migraine is a very prevalent disease with great individual disability and socioeconomic burden. Despite intensive research effort in recent years, the etiopathogenesis of the disease remains to be elucidated. Recently, much importance has been given to mechanisms underlying the cortical excitability that has been suggested to be dysfunctional in migraine. In recent years, noninvasive brain stimulation techniques based on magnetic fields (transcranial magnetic stimulation, TMS) and on direct electrical currents (transcranial direct current stimulation, tDCS) have been shown to be safe and effective tools to explore the issue of cortical excitability, activation, and plasticity in migraine. Moreover, TMS, repetitive TMS (rTMS), and tDCS, thanks to their ability to interfere with and/or modulate cortical activity inducing plastic, persistent effects, have been also explored as potential therapeutic approaches, opening an interesting perspective for noninvasive neurostimulation for both symptomatic and preventive treatment of migraine and other types of headache. In this chapter we critically review evidence regarding the role of noninvasive brain stimulation in the pathophysiology and treatment of migraine, delineating the advantages and limits of these techniques together with potential development and future application.

Pediatric migraine: abortive management in the emergency department

Studies suggest that headache accounts for approximately 1% of pediatric emergency department (ED) visits. ED physicians must distinguish between primary headaches, such as a tension or migraine, and secondary headaches caused by systemic disease including neoplasm, infection, or intracranial hemorrhage. A recent study found that 40% of children presenting to the ED with headache were diagnosed with a primary headache, and 75% of these were migraine. Once the diagnosis of migraine has been made, the ED physician is faced with the challenge of determining appropriate abortive treatment. This review summarizes the most recent literature on pediatric migraine with an emphasis on diagnosis and abortive treatment in the ED.

Pathophysiology of migraine

Migraine is a collection of perplexing neurological conditions in which the brain and its associated tissues have been implicated as major players during an attack. Once considered exclusively a disorder of blood vessels, compelling evidence has led to the realization that migraine represents a highly choreographed interaction between major inputs from both the peripheral and central nervous systems, with the trigeminovascular system and the cerebral cortex among the main players. Advances in in vivo and in vitro technologies have informed us about the significance to migraine of events such as cortical spreading depression and activation of the trigeminovascular system and its constituent neuropeptides, as well as about the importance of neuronal and glial ion channels and transporters that contribute to the putative cortical excitatory/inhibitory imbalance that renders migraineurs susceptible to an attack. This review focuses on emerging concepts that drive the science of migraine in both a mechanistic direction and a therapeutic direction.

Calcium channels and migraine

Missense mutations in CACNA1A, the gene that encodes the pore-forming α1 subunit of human voltage-gated Ca(V)2.1 (P/Q-type) calcium channels, cause a rare form of migraine with aura (familial hemiplegic migraine type 1: FHM1). Migraine is a common disabling brain disorder whose key manifestations are recurrent attacks of unilateral headache that may be preceded by transient neurological aura symptoms. This review, first, briefly summarizes current understanding of the pathophysiological mechanisms that are believed to underlie migraine headache, migraine aura and the onset of a migraine attack, and briefly describes the localization and function of neuronal Ca(V)2.1 channels in the brain regions that have been implicated in migraine pathogenesis. Then, the review describes and discusses i) the functional consequences of FHM1 mutations on the biophysical properties of recombinant human Ca(V)2.1 channels and native Ca(V)2.1 channels in neurons of knockin mouse models carrying the mild R192Q or severe S218L mutations in the orthologous gene, and ii) the functional consequences of these mutations on neurophysiological processes in the cerebral cortex and trigeminovascular system thought to be involved in the pathophysiology of migraine, and the insights into migraine mechanisms obtained from the functional analysis of these processes in FHM1 knockin mice. This article is part of a Special Issue entitled: Calcium channels.

Migraine: a disorder of brain excitatory-inhibitory balance?

Migraine is a common disabling brain disorder whose key manifestations are recurrent attacks of unilateral headache and interictal hypersensitivity to sensory stimuli. Migraine arises from a primary brain dysfunction that leads to episodic activation and sensitization of the trigeminovascular pain pathway and as a consequence to headache. Major open issues concern the molecular and cellular mechanisms of the primary brain dysfunction(s) and of migraine pain. We review here our current understanding of these mechanisms, focusing on recent advances regarding migraine genetics, headache mechanisms, and the primary brain dysfunction(s) underlying migraine onset and susceptibility to cortical spreading depression, the neurophysiological correlate of migraine aura. We also discuss insights obtained from the functional analysis of familial hemiplegic migraine mouse models.

Cortical inhibition at rest and under a focused attention challenge in adults with migraine with and without aura

Objectives: We aimed to further elucidate the functional and attentional regulation of cortical excitability in migraine patients.

Methods: We investigated the cortical silent period (CSP) after transcranial magnetic stimulation as a measure of cortical inhibition under three conditions: resting condition, cortical preactivation during reaction preparation, and during the post-processing of a motor response using a visual contingent negative variation paradigm in adults with migraine with aura, migraine without aura and healthy controls.

Results: CSP was reduced in individuals with migraine with aura and unaffected in those with migraine without aura under resting conditions. Along with the intensity of transcranial magnetic stimulation, CSP increased equally in all groups (equal slopes). Furthermore, the functional challenge by a contingent negative variation task requiring focused sustained attention led to a comparable reduction of CSP duration in all groups.

Discussion: Our data provide further hints towards the conclusion that a specific cortical inhibition deficit in migraine with aura but not migraine without aura is due to a tonic imbalance and not related to increased reactions to phasic stressors. Given that CSP at rest is related to GABA-ergic inhibition whereas the CSP reduction during late contingent negative variation is thought to be related to dopaminergic disinhibition in the basal ganglia, our results point towards reduced GABA-ergic cortical inhibition related to dysfunctional thalamo-cortical loops, especially in migraine with aura.

The routine circular coil is reliable in paired-TMS studies

OBJECTIVE

Motor cortex excitability can be measured by transcranial magnetic stimulation (TMS) using different coil types, but paired-TMS was originally devised with a figure-of-eight coil. We asked whether the most popular, circular coil was suited to the every-day assessment of cortical excitability, particularly paired-TMS indexes, and if it reduced the measurement error.

METHODS

We studied 12 right-handed, healthy subjects (34±7.6 years). Resting motor threshold (MT), cortical silent period (CSP), short-interval intracortical inhibition (SICI) at the 2, 3, 4 and 5 ms interstimulus intervals (ISIs) and intracortical facilitation (ICF) at the 14 and 16 ms ISIs were measured. Intrinsic variability of these indexes was evaluated in terms of Coefficients of Variation, to estimate the measurement error. This sequence was carried out both using a figure-of-eight coil over the hand motor area and a circular coil centred at the vertex. Testing was repeated 8-13 months later.

RESULTS

On average, MT, SICI and ICF did not show any statistically significant difference (p>0.05) when studied with the figure-of-eight as compared with the circular coil. CSP was significantly shorter (p=0.007) with the figure-of-eight coil. Using either coil did not affect measurement variability. There was no significant session-to-session group difference at any of the variables using either coil type.

CONCLUSIONS

Except for the CSP duration, the TMS testing and retesting of cortical excitability, particularly the paired-pulse indexes, did not vary significantly as a function of the coil used.

SIGNIFICANCE

Routine circular coils can be used reliably in paired-TMS studies designed to measure longitudinal changes in cortical excitability though they do not reduce the measurement error.

Peri-ictal changes of cortical excitability in children suffering from migraine without aura

In adult patients with migraine, transcranial magnetic stimulation (TMS) has been used to examine cortical excitability between attacks, but there have been discrepant results. No TMS study has examined cortical excitability in children or adolescents with migraine. Here, we employed TMS to study regional excitability of the occipital (phosphene threshold [PT] and suppression of visual perception) and motor (resting motor threshold and cortical silent period) cortex in ten children suffering from migraine without aura and ten healthy age-matched controls. Patients were studied 1-2 days before and after a migraine attack as well as during the inter-migraine interval. The motion aftereffect was also investigated at each time-point as an index of cortical reactivity to moving visual stimuli. Migraineurs had lower PTs compared to healthy participants at each time-point, indicating increased occipital excitability. This increase in occipital excitability was attenuated 1-2 days before a migraine attack as indicated by a relative increase in PTs. The increase in PTs before the next attack was associated with a stronger TMS-induced suppression of visual perception and a prolongation of the motion aftereffect. Motor cortex excitability was not altered in patients and did not change during the migraine cycle. These findings show that pediatric migraine without aura is associated with a systematic shift in occipital excitability preceding the migraine attack. Similar systematic fluctuations in cortical excitability might be present in adult migraineurs and may reflect either a protective mechanism or an abnormal decrease in cortical excitability that predisposes an individual to a migraine attack.

Reduced cerebellar inhibition in migraine with aura: a TMS study

Subtle clinical cerebellar alterations have been found in migraine. Moreover, abnormalities in visual and motor cortex excitability consistent with a lack of inhibitory efficiency have been described in migraine, and it is known that cerebellum exerts an inhibitory control on cerebral cortex. Here, we investigated if impairment of cerebellar activity on motor cortex, i.e. reduced inhibitory control, can be found in migraine. Ten migraineurs with aura and seven healthy controls underwent a transcranial magnetic stimulation (TMS) protocol to investigate the cerebellar inhibitory drive on motor cortex: a conditioning pulse on right cerebellar cortex was delivered 5, 7, 10, 15 ms before a test stimulus (TS) on contralateral motor cortex. The cerebellar conditioning stimulus inhibits the size of the motor-evoked potential (MEP) produced by the TS alone by approximately 30-50%. Amplitude of MEP to TS alone showed no significant difference between patients and controls. Cerebellar conditioning TMS showed a significant deficit of cerebellar inhibition in migraine patients as compared to controls at all interstimulus intervals (5-15 ms) tested. Cerebellar inhibition is reduced in migraineurs. This could account, at least in part, for the reduced inhibitory efficiency previously showed in cerebral cortex of these patients.

Cortical inhibition and habituation to evoked potentials: relevance for pathophysiology of migraine

Dysfunction of neuronal cortical excitability has been supposed to play an important role in etiopathogenesis of migraine. Neurophysiological techniques like evoked potentials (EP) and in the last years non-invasive brain stimulation techniques like transcranial magnetic stimulation (TMS) and transcranial direct current stimulation gave important contribution to understanding of such issue highlighting possible mechanisms of cortical dysfunctions in migraine. EP studies showed impaired habituation to repeated sensorial stimulation and this abnormality was confirmed across all sensorial modalities, making defective habituation a neurophysiological hallmark of the disease. TMS was employed to test more directly cortical excitability in visual cortex and then also in motor cortex. Contradictory results have been reported pointing towards hyperexcitability or on the contrary to reduced preactivation of sensory cortex in migraine. Other experimental evidence speaks in favour of impairment of inhibitory circuits and analogies have been proposed between migraine and conditions of sensory deafferentation in which down-regulation of GABA circuits is considered the more relevant pathophysiological mechanism. Whatever the mechanism involved, it has been found that repeated sessions of high-frequency rTMS trains that have been shown to up-regulate inhibitory circuits could persistently normalize habituation in migraine. This could give interesting insight into pathophysiology establishing a link between cortical inhibition and habituation and opening also new treatment strategies in migraine.

Is the cerebral cortex hyperexcitable or hyperresponsive in migraine?

Although migraineurs appear in general to be hypersensitive to external stimuli, they maybe also have increased daytime sleepiness and complain of fatigue. Neurophysiological studies between attacks have shown that for a number of different sensory modalities the migrainous brain is characterised by a lack of habituation of evoked responses. Whether this is due to increased cortical hyperexcitability, possibly due to decreased inhibition, or to an abnormal responsivity of the cortex due a decreased preactivation level remains disputed. Studies using transcranial magnetic stimulation in particular have yielded contradictory results. We will review here the available data on cortical excitability obtained with different methodological approaches in patients over the migraine cycle. We will show that these data congruently indicate that the sensory cortices of migraineurs react excessively to repetitive, but not to single, stimuli and that the controversy above hyper- versus hypo-excitability is merely a semantic misunderstanding. Describing the migrainous brain as 'hyperresponsive' would fit most of the available data. Deciphering the precise cellular and molecular underpinnings of this hyperresponsivity remains a challenge for future research. We propose, as a working hypothesis, that a thalamo-cortical dysrhythmia might be the culprit.