Abnormal facilitatory mechanisms in motor cortex of migraine with aura

White matter and cortical gray matter microstructural abnormalities in new daily persistent headache: a NODDI study

BACKGROUND

New daily persistent headache (NDPH) is a rare primary headache with unclear pathogenesis. Neuroimaging studies of NDPH are limited, and controversy still exists. Diffusion tensor imaging (DTI) is commonly used to study the white matter. However, lacking specificity, the potential pathological mechanisms of white matter microstructural changes remain poorly understood. In addition, the intricacy of gray matter structures impedes the application of the DTI model. Here, we applied an advanced diffusion model of neurite orientation dispersion and density imaging (NODDI) to study the white matter and cortical gray matter microstructure in patients with NDPH.

METHODS

This study assessed brain microstructure, including 27 patients with NDPH, and matched 28 healthy controls (HCs) by NODDI. The differences between the two groups were assessed by tract-based spatial statistics (TBSS) and surface-based analysis (SBA), focusing on the NODDI metrics (neurite density index (NDI), orientation dispersion index (ODI), and isotropic volume fraction (ISOVF)). Furthermore, we performed Pearson's correlation analysis between the NODDI indicators and clinical characteristics.

RESULTS

Compared to HCs, patients with NDPH had a reduction of density and complexity in several fiber tracts. For robust results, the fiber tracts were defined as comprising more than 100 voxels, including bilateral inferior fronto-occipital fasciculus (IFOF), left superior longitudinal fasciculus (SLF) and inferior longitudinal fasciculus (ILF), as well as right corticospinal tract (CST). Moreover, the reduction of neurite density was uncovered in the left superior and middle frontal cortex, left precentral cortex, and right lateral orbitofrontal cortex and insula. There was no correlation between the NODDI metrics of these brain regions and clinical variables or scales of relevance after the Bonferroni correction.

CONCLUSIONS

Our research indicated that neurite loss was detected in both white matter and cortical gray matter of patients with NDPH.

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.

Alterations of amygdala volume and functional connectivity in migraine patients comorbid with and without depression

OBJECTIVE

The comorbid relationship between migraine and depression has been well recognized, but its underlying pathophysiology is unclear. Here, we aimed to explore the structural changes of the amygdala and the abnormal functional connectivity of the centromedial amygdala (CMA) in migraineurs with depression.

METHODS

High-resolution T1-weighted and functional magnetic resonance images were acquired from 22 episodic migraineurs with comorbid depression (EMwD), 21 episodic migraineurs without depression (EM), and 17 healthy controls (HC). Voxel-based morphometry and resting-state functional connectivity (rsFC) were applied to examine the intergroup differences in amygdala volume.

RESULTS

The bilateral amygdala volume was increased in the EMwD and EM groups compared with the HC group, but there were no differences between the EMwD and EM groups. The right CMA exhibited decreased rsFC in the left dorsolateral prefrontal cortex (DLPFC) in the EMwD group compared with the EM group, while rsFC increased between the CMA and the contralateral DLPFC in the EM group compared with the HC group. In addition, the EM group showed decreased rsFC between the left CMA and the left pallidum compared with the HC group.

CONCLUSIONS

Enlarged amygdala is an imaging feature of EM and EMwD. The inconsistency of rsFC between CMA and DLPFC between migraineurs with and without depression might indicate that decreased rsFC between CMA and DLPFC is a neuropathologic marker for the comorbidity of migraine and depression. The core regions might be a potential intervention target for the treatment of EMwD in the future.

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.

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.

Modulation of Human Motor Cortical Excitability and Plasticity by Opuntia Ficus Indica Fruit Consumption: Evidence from a Preliminary Study through Non-Invasive Brain Stimulation

Indicaxanthin (IX) from Opuntia Ficus Indica (OFI) has been shown to exert numerous biological effects both in vitro and in vivo, such as antioxidant, anti-inflammatory, neuro-modulatory activity in rodent models. Our goal was to investigate the eventual neuro-active role of orally assumed fruits containing high levels of IX at nutritionally-relevant amounts in healthy subjects, exploring cortical excitability and plasticity in the human motor cortex (M1). To this purpose, we applied paired-pulse transcranial magnetic stimulation and anodal transcranial direct current stimulation (a-tDCS) in basal conditions and followed the consumption of yellow cactus pear fruits containing IX or white cactus pear fruits devoid of IX (placebo). Furthermore, resting state-functional MRI (rs-fMRI) preliminary acquisitions were performed before and after consumption of the same number of yellow fruits. Our data revealed that the consumption of IX-containing fruits could specifically activate intracortical excitatory circuits, differently from the placebo-controlled group. Furthermore, we found that following the ingestion of IX-containing fruits, elevated network activity of glutamatergic intracortical circuits can homeostatically be restored to baseline levels following a-tDCS stimulation. No significant differences were observed through rs-fMRI acquisitions. These outcomes suggest that IX from OFI increases intracortical excitability of M1 and leads to homeostatic cortical plasticity responses.

Noninvasive Neuromodulation in Headache: An Update

Background

Migraine is a common disabling primary headache condition. Although strives have been made in treatment, there remains an unmet need for safe, effective acute, and preventative treatments. The promising concept of neuromodulation of relevant neuronal targets in a noninvasive fashion for the treatment of primary headache disorders has led to the trial of numerous devices over the years.

Objective

We aimed to review the evidence on current neuromodulation treatments available for the management of primary headache disorders.

Methods

Randomized controlled trial as well as open-label and real-world studies on central and peripheral cephalic and noncephalic neuromodulation modalities in primary headaches were critically reviewed.

Results

The current evidence suggests a role of single-pulse transcranial magnetic stimulation, supraorbital nerve stimulation, and remote noncephalic electrical stimulation as migraine abortive treatments, with stronger evidence in episodic rather than in chronic migraine. Single-pulse transcranial magnetic stimulation and supraorbital nerve stimulation also hold promising evidence in episodic migraine prevention and initial positive evidence in chronic migraine prevention. More evidence should clarify the therapeutic role of the external vagus nerve stimulation and transcranial direct current stimulation in migraine. However, external vagus nerve stimulation may be effective in the acute treatment of episodic but not chronic cluster headache, in the prevention of hemicrania continua and paroxysmal hemicrania but not of short-lasting neuralgiform headache attacks. The difficulty in setting up sham-controlled studies has thus far prevented the publication of robust trials. This limitation along with the cost of these therapies has meant that their use is limited in most countries.

Conclusion

Neuromodulation is a promising nonpharmacological treatment approach for primary headaches. More studies with appropriate blinding strategies and reduction of device cost may allow more widespread approval of these treatments and in turn increase clinician's experience in neuromodulation.

Aberrant plasticity in musculoskeletal pain: a failure of homeostatic control?

Aberrant synaptic plasticity is hypothesised to underpin chronic pain. Yet, synaptic plasticity regulated by homeostatic mechanisms have received limited attention in pain. We investigated homeostatic plasticity in the human primary motor cortex (M1) of 21 healthy individuals in response to experimentally induced muscle pain for several days. Experimental pain was induced by injecting nerve growth factor into the muscle belly of the right extensor carpi radialis brevis muscle. Pain and disability were monitored until day 21. Homeostatic plasticity was induced on day 0, 2, 4, 6, and 14 in the left M1 using anodal transcranial direct stimulation (tDCS) applied for 7 and 5 min, separated by a 3-min rest period. Motor-evoked potentials (MEP) to transcranial magnetic stimulation assessed the homeostatic response. On days 0 and 14, MEPs increased following the first block of tDCS (p < 0.004), and decreased following the second block of tDCS (p < 0.001), consistent with a normal homeostatic response. However, on days 2 (p = 0.07) and 4 (p = 0.7), the decrease in MEPs after the second block of tDCS was attenuated, representing an impaired homeostatic response. Findings demonstrate altered homeostatic plasticity in the M1 with the greatest alteration observed after 4 days of sustained pain. This study provides longitudinal insight into homeostatic plasticity in response to the development, maintenance, and resolution of pain over the course of 14 days.

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.

Migraine and Sport in a Physically Active Population of Students: Results of a Cross-Sectional Study

OBJECTIVE

In this study, we explored the relationship between migraine and sport in a physically active population of students, analyzing the risk of migraine among sporty students.

BACKGROUND

The relationship between sport and migraine is controversial; moreover, several studies report on sport as a migraine trigger, but there is evidence that physical activity could have a relevant role in migraine prevention.

METHODS

A cross-sectional survey was conducted using the validated ID-migraine questionnaire including specific demo-anthropometric (gender, age, weight, height) and sports variables on a potentially active student population of the University of Palermo. Evaluation in putative migraine subjects of clinical features and disability was explored through the administration of the Italian version of the Migraine Disability Assessment Scale. Statistical analyses were performed using univariate and logistic regression analyses.

RESULTS

Three hundred and ninety-three out of 520 students (210 F, mean age: 23.5 ± 0.7 years; 183 M; mean age: 20.5 ± 0.7 years) participated in this study. Migraine screened positive in 102 subjects (26.0%) and its prevalence was significantly higher among females (P < .001). An increased risk of migraine was found in females, and a protective effect of sport on the risk of migraine among females, but not among males.

CONCLUSIONS

The role of exercise in migraine is still unclear. This study supports a protective role of sport in migraine reporting a protective effect in females. Further studies are needed to deepen the association between sport and migraine.

Multisensorial Perception in Chronic Migraine and the Role of Medication Overuse

Multisensory processing can be assessed by measuring susceptibility to crossmodal illusions such as the Sound-Induced Flash Illusion (SIFI). When a single flash is accompanied by 2 or more beeps, it is perceived as multiple flashes (fission illusion); conversely, a fusion illusion is experienced when more flashes are matched with a single beep, leading to the perception of a single flash. Such illusory perceptions are associated to crossmodal changes in visual cortical excitability. Indeed, increasing occipital cortical excitability, by means of transcranial electrical currents, disrupts the SIFI (ie, fission illusion). Similarly, a reduced fission illusion was shown in patients with episodic migraine, especially during the attack, in agreement with the pathophysiological model of cortical hyperexcitability of this disease. If episodic migraine patients present with reduced SIFI especially during the attack, we hypothesize that chronic migraine (CM) patients should consistently report less illusory effects than healthy controls; drugs intake could also affect SIFI. On such a basis, we studied the proneness to SIFI in CM patients (n = 63), including 52 patients with Medication Overuse Headache (MOH), compared to 24 healthy controls. All migraine patients showed reduced fission phenomena than controls (P < .0001). Triptan MOH patients (n = 23) presented significantly less fission effects than other CM groups (P = .008). This exploratory study suggests that CM - both with and without medication overuse - is associated to a higher visual cortical responsiveness which causes deficit of multisensorial processing, as assessed by the SIFI. PERSPECTIVE: This observational study shows reduced susceptibility to the SIFI in CM, confirming and extending previous results in episodic migraine. MOH contributes to this phenomenon, especially in case of triptans.

Cathodal Occipital tDCS Is Unable to Modulate the Sound Induced Flash Illusion in Migraine

Migraine is a highly disabling disease characterized by recurrent pain. Despite an intensive effort, mechanisms of migraine pathophysiology still represent an unsolved issue. Evidence from both animal and human studies suggests that migraine is characterized by hyperresponsivity or hyperexcitability of sensory cortices, especially the visual cortex. This phenomenon, in turn, may affect multisensory processing. Indeed, migraineurs present with an abnormal, reduced, perception of the Sound-induced Flash Illusion (SiFI), a crossmodal illusion that relies on optimal integration of visual and auditory stimuli by the occipital visual cortex. Decreasing visual cortical excitability with transcranial direct current stimulation (tDCS) can increase the SiFI in healthy subjects. Moving away from these issues, we applied cathodal tDCS over the visual cortex of migraineurs, with and without aura, in order to decrease cortical excitability and thus physiologically restoring the perception of a reliable SiFI. Differently from our expectations, tDCS was unable to reliably modulate SiFI in migraine. The chronic, relatively excessive, visual cortex hyperexcitability, featuring the migraineur brain, may render tDCS ineffective for restoring multisensory processing in this disease.

Clinical neurophysiology of migraine with aura

BACKGROUND

The purpose of this review is to provide a comprehensive overview of the findings of clinical electrophysiology studies aimed to investigate changes in information processing of migraine with aura patients.

MAIN BODY

Abnormalities in alpha rhythm power and symmetry, the presence of slowing, and increased information flow in a wide range of frequency bands often characterize the spontaneous EEG activity of MA. Higher grand-average cortical response amplitudes, an increased interhemispheric response asymmetry, and lack of amplitude habituation were less consistently demonstrated in response to any kind of sensory stimulation in MA patients. Studies with single-pulse and repetitive transcranial magnetic stimulation (TMS) have reported abnormal cortical responsivity manifesting as greater motor evoked potential (MEP) amplitude, lower threshold for phosphenes production, and paradoxical effects in response to both depressing or enhancing repetitive TMS methodologies. Studies of the trigeminal system in MA are sparse and the few available showed lack of blink reflex habituation and abnormal findings on SFEMG reflecting subclinical, probably inherited, dysfunctions of neuromuscular transmission. The limited studies that were able to investigate patients during the aura revealed suppression of evoked potentials, desynchronization in extrastriate areas and in the temporal lobe, and large variations in direct current potentials with magnetoelectroencephalography. Contrary to what has been observed in the most common forms of migraine, patients with familial hemiplegic migraine show greater habituation in response to visual and trigeminal stimuli, as well as a higher motor threshold and a lower MEP amplitude than healthy subjects.

CONCLUSION

Since most of the electrophysiological abnormalities mentioned above were more frequently present and had a greater amplitude in migraine with aura than in migraine without aura, neurophysiological techniques have been shown to be of great help in the search for the pathophysiological basis of migraine aura.

Primary headaches during lifespan

Primary headaches are one of the most prevalent neurological disorders and can occur during a wide range of lifespan. Primary headaches, especially migraine, are cyclic disorders with a complex sequence of symptoms within every headache attack. There is no systematic review of whether these symptoms changes during lifespan. Indeed, the clinical presentation of migraine shows an age-dependent change with a significantly shorter duration of the attacks and occurrence of different paroxysmal symptoms, such as vomiting, abdominal pain or vertigo, in childhood and, in contrast, largely an absence of autonomic signs and a more often bilateral headache in the elderly. The age-dependent differences in the clinical presentation are less distinct in cluster headache and, especially, in tension-type headache. The differences in the clinical presentation are in agreement with the idea that the connectivity of hypothalamic areas with different brainstem areas, especially the central parasympathetic areas, is important for the clinical manifestation of migraine, as well as, the change during lifespan.

Motor corticospinal excitability: a novel facet of pain modulation?

Introduction

Increase in excitability of the primary motor cortex (M1) is associated with pain inhibition by analgesics, which is, in turn, associated with the psychophysical antinociceptive pain modulation profile. However, the relationship between neurophysiological M1 excitability and psychophysical pain modulation has not yet been explored.

Objectives

We aim to study these relationships in healthy subjects.

Methods

Forty-one young healthy subjects (22 women) underwent a wide battery of psychophysical testing that included conditioned pain modulation (CPM) and pain temporal summation, and a transcranial magnetic stimulation neurophysiological assessment of the motor corticospinal excitability, including resting motor threshold, motor-evoked potentials (MEPs), and cortical silent period.

Results

Increased motor corticospinal excitability in 2 parameters was associated with more efficient CPM: (1) higher MEP amplitude (r = -0.574; P _{_Bonferroni} = 0.02) and (2) longer MEP duration (r = -0.543; P _{_Bonferroni} = 0.02). The latter also correlated with the lower temporal summation magnitude (r = -0.421; P = 0.007); however, on multiplicity adjustment, significance was lost.

Conclusions

Increased corticospinal excitability of the primary motor cortex is associated with more efficient inhibitory pain modulation as assessed by CPM, in healthy subjects. Motor-evoked potential amplitude and duration may be considered as an additional, objective and easy to measure parameter to allow for better individual assessment of pain modulation profile.

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.

Short-term cortical synaptic depression/potentiation mechanisms in chronic migraine patients with or without medication overuse

Objective

To study the effects of trains of repetitive transcranial magnetic stimulation (rTMS) over the motor cortex in patients with chronic migraine (CM) with or without medication overuse (MOH).

Subjects and methods

Thirty-two patients (CM [n = 16]; MOH [n = 16]) and 16 healthy volunteers (HVs) underwent rTMS recording. Ten trains of 10 stimuli each (120% resting motor threshold) were applied over the left motor cortex at 1 Hz or 5 Hz in random order. The amplitude of motor evoked potential (MEP) was evaluated from electromyographic recording in the first dorsal interosseous muscle. The slope of the linear regression line for the 10 stimuli for each participant was calculated using normalized data.

Results

rTMS-1 Hz had a normal depressive effect on MEP amplitude in all groups. rTMS-5 Hz depressed instead of potentiating MEP amplitudes in MOH patients, with a significantly different response from that in HVs and CM patients. The slope of the linear regression of MEP amplitudes was negatively correlated with pain intensity in CM patients, and with the duration of overuse headache in MOH patients.

Conclusions

This different plastic behaviour suggests that MOH and CM, despite exhibiting a similar clinical phenotype, have different neurophysiological learning processes, probably related to different pathophysiological mechanisms of migraine chronification.

Test-Retest Reliability of Homeostatic Plasticity in the Human Primary Motor Cortex

Homeostatic plasticity regulates synaptic activity by preventing uncontrolled increases (long-term potentiation) or decreases (long-term depression) in synaptic efficacy. Homeostatic plasticity can be induced and assessed in the human primary motor cortex (M1) using noninvasive brain stimulation. However, the reliability of this methodology has not been investigated. Here, we examined the test-retest reliability of homeostatic plasticity induced and assessed in M1 using noninvasive brain stimulation in ten, right-handed, healthy volunteers on days 0, 2, 7, and 14. Homeostatic plasticity was induced in the left M1 using two blocks of anodal transcranial direct current stimulation (tDCS) applied for 7 min and 5 min, separated by a 3 min interval. To assess homeostatic plasticity, 15 motor-evoked potentials to single-pulse transcranial magnetic stimulation were recorded at baseline, between the two blocks of anodal tDCS, and at 0 min, 10 min, and 20 min follow-up. Test-retest reliability was evaluated using intraclass correlation coefficients (ICCs). Moderate-to-good test-retest reliability was observed for the M1 homeostatic plasticity response at all follow-up time points (0 min, 10 min, and 20 min, ICC range: 0.43-0.67) at intervals up to 2 weeks. The greatest reliability was observed when the homeostatic response was assessed at 10 min follow-up (ICC > 0.61). These data suggest that M1 homeostatic plasticity can be reliably induced and assessed in healthy individuals using two blocks of anodal tDCS at intervals of 48 hours, 7 days, and 2 weeks.

The Effects of Repetitive Transcranial Magnetic Stimulation at Dorsolateral Prefrontal Cortex in the Treatment of Migraine Comorbid with Depression: A Retrospective Open Study

Objective

The literature on managing migraine non-responsive to pharmacological approaches and that co-occurring with depression is scanty. The comorbid condition predicts a poorer prognosis for migraine as well as depression. The present report assesses efficacy and tolerability of high frequency repetitive transcranial magnetic stimulation (rTMS) over left dorsolateral prefrontal cortex as a treatment modality for migraine with comorbid depression.

Methods

The current retrospective chart review assesses effectiveness of high frequency rTMS over left dorsolateral prefrontal cortex as a treatment modality to manage migraine occurring comorbid with depression in 14 subjects.

Results

The mean scores on Migraine Disability Assessment Test (MIDAS) and depression rating scale reduced significantly from 21.14±3.01 and 20.71±3.95 at baseline to 13.93±6.09 and 14.21±5.52 respectively, after rTMS. There was significant improvement in migraine frequency, severity and functional disability assessed using MIDAS scores (p＜0.05) following high frequency rTMS compared to baseline.

Conclusion

There is a role of applying rTMS as a potential therapeutic modality in the integrated management of a distinct subgroup of migraine patients with comorbid depression.

Disruption of cortical synaptic homeostasis in individuals with chronic low back pain

OBJECTIVE

Homeostatic plasticity mechanisms regulate synaptic plasticity in the human brain. Impaired homeostatic plasticity may contribute to maladaptive synaptic plasticity and symptom persistence in chronic musculoskeletal pain.

METHODS

We examined homeostatic plasticity in fifty individuals with chronic low back pain (cLBP) and twenty-five pain-free controls. A single block (7-min) of anodal transcranial direct current stimulation ('single tDCS'), or two subsequent blocks (7-min and 5-min separated by 3-min rest; 'double tDCS'), were randomised across two experimental sessions to confirm an excitatory response to tDCS applied alone, and evaluate homeostatic plasticity, respectively. Corticomotor excitability was assessed in the corticomotor representation of the first dorsal interosseous muscle by transcranial magnetic stimulation-induced motor evoked potentials (MEPs) recorded before and 0, 10, 20, and 30-min following each tDCS protocol.

RESULTS

Compared with baseline, MEP amplitudes increased at all time points in both groups following the single tDCS protocol (P < 0.003). Following the double tDCS protocol, MEP amplitudes decreased in pain-free controls at all time points compared with baseline (P < 0.01), and were unchanged in the cLBP group.

CONCLUSION

These data indicate impaired homeostatic plasticity in the primary motor cortex of individuals with cLBP.

SIGNIFICANCE

Impaired homeostatic plasticity could explain maladaptive synaptic plasticity and symptom persistence in cLBP.

Excitability of the motor cortex in patients with migraine changes with the time elapsed from the last attack

Background

Motor-evoked potentials (MEPs) produced by single-pulse transcranial magnetic stimulation (TMS) of the motor cortex can be an objective measure of cortical excitability. Previously, MEP thresholds were found to be normal, increased, or even reduced in patients with migraine. In the present study, we determined whether the level of cortical excitability changes with the time interval from the last migraine attack, thereby accounting for the inconsistencies in previous reports.

Methods

Twenty-six patients with untreated migraine without aura (MO) underwent a MEP study between attacks. Their data were then compared to the MEP data collected from a group of 24 healthy volunteers (HVs). During the experiment, the TMS figure-of-eight coil was positioned over the left motor area. After identifying the resting motor threshold (RMT), we delivered 10 single TMS pulses (rate: 0.1 Hz, intensity: 120% of the RMT) and averaged the resulting MEP amplitudes.

Results

The mean RMTs and MEP amplitudes were not significantly different between the MO and HV groups. In patients with MO, the RMTs were negatively correlated with the number of days elapsed since the last migraine attack (rho = -0.404, p = 0.04).

Conclusion

Our results suggest that the threshold for evoking MEPs is influenced by the proximity of an attack; specifically, the threshold is lower when a long time interval has passed after an attack, and is higher (within the range of normative values) when measured close to an attack. These dynamic RMT variations resemble those we reported previously for visual and somatosensory evoked potentials and may represent time-dependent plastic changes in brain excitability in relation to the migraine cycle.

Genetic insights into migraine and glutamate: a protagonist driving the headache

Migraine is a complex polygenic disorder that continues to be a great source of morbidity in the developed world with a prevalence of 12% in the Caucasian population. Genetic and pharmacological studies have implicated the glutamate pathway in migraine pathophysiology. Glutamate profoundly impacts brain circuits that regulate core symptom domains in a range of neuropsychiatric conditions and thus remains a "hot" target for drug discovery. Glutamate has been implicated in cortical spreading depression (CSD), the phenomenon responsible for migraine with aura and in animal models carrying FHM mutations. Genotyping case-control studies have shown an association between glutamate receptor genes, namely, GRIA1 and GRIA3 with migraine with indirect supporting evidence from GWAS. New evidence localizes PRRT2 at glutamatergic synapses and shows it affects glutamate signalling and glutamate receptor activity via interactions with GRIA1. Glutamate-system defects have also been recently implicated in a novel FHM2 ATP1A2 disease-mutation mouse model. Adding to the growing evidence neurophysiological findings support a role for glutamate in cortical excitability. In addition to the existence of multiple genes to choreograph the functions of fast-signalling glutamatergic neurons, glutamate receptor diversity and regulation is further increased by the post-translational mechanisms of RNA editing and miRNAs. Ongoing genetic studies, GWAS and meta-analysis implicate neurogenic mechanisms in migraine pathology and the first genome-wide associated locus for migraine on chromosome X. Finally, in addition to glutamate modulating therapies, the kynurenine pathway has emerged as a candidate for involvement in migraine pathophysiology. In this review we discuss recent genetic evidence and glutamate modulating therapies that bear on the hypothesis that a glutamatergic mechanism may be involved in migraine susceptibility.

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.

Migraine affects white-matter tract integrity: A diffusion-tensor imaging study

BACKGROUND

Specific white-matter tract alterations in migraine remain to be elucidated. Using diffusion tensor imaging (DTI), this study investigated whether the integrity of white-matter tracts that underlie regions of the "pain matrix" is altered in migraine and interrogated whether the number of years lived with migraine modifies fibertract structure.

METHODS

Global probabilistic tractography was used to assess the anterior thalamic radiations, the corticospinal tracts and the inferior longitudinal fasciculi in 23 adults with migraine and 18 healthy controls.

RESULTS

Migraine patients show greater mean diffusivity (MD) in the left and right anterior thalamic radiations, the left corticospinal tract, and the right inferior longitudinal fasciculus tract. Migraine patients also show greater radial diffusivity (RD) in the left anterior thalamic radiations, the left corticospinal tract as well as the left and right inferior longitudinal fasciculus tracts. No group fractional anisotropy (FA) differences were identified for any tracts. Migraineurs showed a positive correlation between years lived with migraine and MD in the right anterior thalamic radiations (r = 0.517; p = 0.012) and the left corticospinal tract (r = 0.468; p = 0.024).

CONCLUSION

Results indicate that white-matter integrity is altered in migraine and that longer migraine history is positively correlated with greater alterations in tract integrity.

Transcranial magnetic stimulation for chronic pain

Current data suggest that transcranial magnetic stimulation (TMS) has the potential to be an effective and complimentary treatment modality for patients with chronic neuropathic pain syndromes. The success of TMS for pain relief depends on the parameters of the stimulation delivered, the location of neural target, and duration of treatment. TMS can be used to excite or inhibit underlying neural tissue that depends on long-term potentiation and long-term depression, respectively. Long-term randomized controlled studies are warranted to establish the efficacy of repetitive TMS in patients with various chronic pain syndromes.

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.

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.

Modulation of visual evoked potentials by high-frequency repetitive transcranial magnetic stimulation in migraineurs

OBJECTIVE

High-frequency repetitive transcranial magnetic stimulation (rTMS) modulates cortical excitability. We investigated its effect on visual evoked potentials (VEPs) in migraine.

METHODS

Thirty-two headache-free controls (CO), 25 interictal (MINT) and 7 preictal migraineurs (MPRE) remained after exclusions. VEPs to 8' and 65' checks were averaged in six blocks of 100 single responses. VEPs were recorded before, directly after and 25min after 10Hz rTMS. The study was blinded for diagnosis during recording and for diagnosis and block number during analysis. First block amplitudes and habituation (linear amplitude change over blocks) were analysed with repeated measures ANOVA.

RESULTS

With 65' checks, N70-P100 habituation was reduced in MINT compared to CO after rTMS (p=0.013). With 8' checks, habituation was reduced in MPRE compared to MINT and CO after rTMS (p<0.016). No effects of rTMS on first block amplitudes were found.

CONCLUSION

RTMS reduced habituation only in migraineurs, indicating increased responsivity to rTMS. The magnocellular visual subsystem may be affected interictally, while the parvocellular system may only be affected preictally.

SIGNIFICANCE

Migraineurs may have increased responsiveness to rTMS because of a cortical dysfunction that changes before a migraine attack.

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.

Neuromodulation of chronic headaches: position statement from the European Headache Federation

The medical treatment of patients with chronic primary headache syndromes (chronic migraine, chronic tension-type headache, chronic cluster headache, hemicrania continua) is challenging as serious side effects frequently complicate the course of medical treatment and some patients may be even medically intractable. When a definitive lack of responsiveness to conservative treatments is ascertained and medication overuse headache is excluded, neuromodulation options can be considered in selected cases. Here, the various invasive and non-invasive approaches, such as hypothalamic deep brain stimulation, occipital nerve stimulation, stimulation of sphenopalatine ganglion, cervical spinal cord stimulation, vagus nerve stimulation, transcranial direct current stimulation, repetitive transcranial magnetic stimulation, and transcutaneous electrical nerve stimulation are extensively published although proper RCT-based evidence is limited. The European Headache Federation herewith provides a consensus statement on the clinical use of neuromodulation in headache, based on theoretical background, clinical data, and side effect of each method. This international consensus further gives recommendations for future studies on these new approaches. In spite of a growing field of stimulation devices in headaches treatment, further controlled studies to validate, strengthen and disseminate the use of neurostimulation are clearly warranted. Consequently, until these data are available any neurostimulation device should only be used in patients with medically intractable syndromes from tertiary headache centers either as part of a valid study or have shown to be effective in such controlled studies with an acceptable side effect profile.

Electrophysiological correlates of episodic migraine chronification: evidence for thalamic involvement

Background

Episodic migraine is characterized by decreased high-frequency somatosensory oscillations (HFOs), reflecting thalamo-cortical activity, and deficient habituation of low-frequency (LF-) somatosensory evoked potentials (SSEPs) to repetitive sensory stimulation between attacks. Here, we study conventional LF-SSEPs and HFOs in episodic migraineurs who developed chronic migraine (CM).

Methods

Thirty-four episodic (15 interictally [MOii], 19 ictally [MOi]) and 19 CM patients underwent right median nerve SSEPs. The patient groups were compared to a group of 20 healthy volunteers (HV) of comparable age and gender distribution. We measured the N20-P25 LF-SSEP 1st amplitude block and habituation, and, after applying a band-pass filter (450–750 Hz), maximal peak-to-peak latency and the amplitudes of the early and late HFOs.

Results

Reduced early HFOs, lower 1st block LF-SSEPs and deficient habituation characterize MOii. Initially higher SSEP amplitudes and late normal habituation characterize both CM and MOi patients. After the digital filtration, both patient groups showed shortened latency peaks and normalization of early HFO amplitudes with increased late HFOs. When data of MO and CM patients were combined, the monthly number of days with headache negatively correlated with the LF-SSEP slope (r = −0.385, p = 0.006), which in turn negatively correlated with the 1st amplitude block (r = 0.568, p < 0.001).

Conclusions

Our results show abnormalities in chronic migraine that are also reported during attacks in episodic migraineurs, namely early response sensitization and late habituation. The HFO analysis suggests that this sensory sensitization may be explained by an increase in the strength of the connections between the thalamus and cortex compared to episodic migraine between attacks. Whether this electro-functional behaviour is primary or secondary to daily headache, thus reflecting an electrophysiological fingerprint of the somatosensory system central sensitization process, remains to be determined.

Lateral inhibition in visual cortex of migraine patients between attacks

Background

The interictal deficit of habituation to repetitive visual stimuli in migraine patients could be due to deficient intracortical inhibition and/or to low cortical pre-activation levels. Which of these abnormalities contributes more to the habituation deficit cannot be determined with the common methods used to record transient visual responses.

We investigated lateral inhibition in the visual cortex during the migraine cycle and in healthy subjects by using differential temporal modulations of radial windmill-dartboard (WD) or partial-windmill (PW) visual patterns.

Methods

Transient (TR-VEP) and steady-state visual-evoked potentials (SS-VEP) were recorded in 65 migraine patients (21 without and 22 with aura between attacks; 22 patients during an attack) and in 21 healthy volunteers (HV). Three stimulations were used in each subject: classic checkerboard pattern (contrast-reversion 3.1Hz), WD and PW (contrast-reversion ~4Hz). For each randomly presented stimulation protocol, 600 sweeps were acquired and off-line partitioned in 6 blocks of 100. Fourier analysis allowed data to extract in SS-VEP the fundamental (1H) and the second harmonic (2H) components that reflect respectively short-(WD) and long- range lateral inhibition (attenuation of 2H in WD compared to PW).

Results

Compared to HV, migraineurs recorded interictally had significantly less habituation of the N1-P1 TR-VEP component over subsequent blocks and they tended to have a smaller 1^st block amplitude. 1H amplitude in the 1^st block of WD SS-VEP was significantly greater than in HV and habituated in successive blocks, contrasting with an amplitude increase in HV. Both the interictal TR-VEP and SS-VEP abnormalities normalized during an attack. There was no significant between group difference in the PW 2H amplitude and its attenuation. When data of HV and migraine patients were combined, the habituation slope of WD-VEP 1H was negatively correlated with that of TR-VEP N1-P1 and with number of days since the last migraine attack.

Conclusion

These results are in favour of a migraine cycle-dependent imbalance between excitation and inhibition in the visual cortex. We hypothesize that an interictal hypoactivity of monaminergic pathways may cause a functional disconnection of the thalamus in migraine leading to an abnormal intracortical short-range lateral inhibition that could contribute to the habituation deficit observed during stimulus repetition.