Exploring the Therapeutic Potential of Quadripulse rTMS over the Visual Cortex: A Proof-of-Concept Study in Healthy Volunteers and Chronic Migraine Patients with Medication Overuse Headache

In chronic migraine with medication overuse (CM-MOH), sensitization of visual cortices is reflected by (i) increased amplitude of stimulus-evoked responses and (ii) habituation deficit during repetitive stimulation. Both abnormalities might be mitigated by inhibitory transcranial neurostimulation. Here, we tested an inhibitory quadripulse repetitive transcranial magnetic stimulation (rTMS-QPI) protocol to decrease durably visual cortex excitability in healthy subjects (HS) and explored its therapeutic potential in CM-MOH patients. Pattern-reversal visual evoked potentials (VEP) were used as biomarkers of effect and recorded before (T1), immediately after (T2), and 3 h after stimulation (T3). In HS, rTMS-QPI durably decreased the VEP 1st block amplitude (p < 0.05) and its habituation (p < 0.05). These changes were more pronounced for the P1N2 component that was modified already at T2 up to T3, while for N1P1 they were significant only at T3. An excitatory stimulation protocol (rTMS-QPE) tended to have an opposite effect, restricted to P1N2. In 12 CM-MOH patients, during a four-week treatment (2 sessions/week), rTMS-QPI significantly reduced monthly headache days (p < 0.01). In patients reversing from CM-MOH to episodic migraine (n = 6), VEP habituation significantly improved after treatment (p = 0.005). rTMS-QPI durably decreases visual cortex responsivity in healthy subjects. In a proof-of-concept study of CM-MOH patients, rTMS-QPI also has beneficial clinical and electrophysiological effects, but sham-controlled trials are needed.

Non-Pharmacological Treatment for Chronic Migraine

PURPOSE OF REVIEW

Chronic migraine (CM) affects a large proportion of the population and is a significant source of disability and lost productivity. Numerous non-pharmacological approaches have been attempted during the past decades. This review discusses the most recent and evidence-based advances in acute and preventive non-pharmacological therapeutic approaches for CM, offering alternatives to drug treatment.

RECENT FINDINGS

A growing number of non-pharmacological treatment options, including non-invasive or invasive neuromodulation, acupuncture, psychotherapy, and physiotherapy, have shown promising efficacy in CM. There is strong evidence for the effectiveness of non-invasive neuromodulation such as transcranial magnetic stimulation, transcranial direct current stimulation, and transcutaneous electrical nerve stimulation (TENS) in CM, but less evidence for approaches such as invasive neuromodulation, physical therapy, or dietary approaches. Acupuncture for migraine remains controversial, with the main point of contention still being the placebo effect. Non-pharmacological approaches can be offered as a reliable alternative for patients with CM, and more research is being done to evaluate the efficacy of non-invasive neuromodulation with different parameters and the combination of different treatments in CM.

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.

Topographic localization of migraine triggers and its association with headache frequency and severity

OBJECTIVE

Internal biological rhythm with or without external trigger may precipitate migraine. Classifying exogenous and endogenous triggers to a topographic localization may help in understanding the migraine. We report topographic localization of migraine triggers and its influence on headache frequency and severity.

METHODS

588 migraineurs, aged 16-69 years were included. Various endogenous and exogenous triggers were categorized to topographic localization- hypothalamic, pituitary, auditory, visual, somato-sensory, olfactory and gustatory. The relationship of topographic localization of triggers with episodic versus chronic migraine, and moderate versus severe headache were analyzed using univariate followed by multivariate analysis.

RESULTS

All migraineurs had triggers 584(99.9%) except 4(0.1%) patients. Presence of multiple triggers (99.4%), and combination of both endogenous and exogenous triggers (97.7%) was the rule. On topographic localization, hypothalamic trigger was the commonest (98.1%) followed by visual (84.1%), auditory (82.1%), somatosensory (76.1%), olfactory (26.2%), pituitary (24.1%), and gustatory (6.6%). 98.6% patients had combination of hypothalamic with pituitary triggers. Hypothalamic [Adjusted odds ratio (AOR) 4.50] and auditory triggers (AOR 0.34) independently predicted chronic migraine, and auditory (AOR 0.55) and gustatory (AOR 2.41) triggers predicted severity of headache.

CONCLUSION

Hypothalamic triggers are the commonest suggesting an innate susceptibility of migraine. Auditory trigger may precipitate frequent and severe headache.

A C-shaped miniaturized coil for transcranial magnetic stimulation in rodents

Objective.Transcranial magnetic stimulation (TMS) is a non-invasive technique widely used for neuromodulation. Animal models are essential for investigating the underlying mechanisms of TMS. However, the lack of miniaturized coils hinders the TMS studies in small animals, since most commercial coils are designed for humans and thus incapable of focal stimulation in small animals. Furthermore, it is difficult to perform electrophysiological recordings at the TMS focal point using conventional coils.Approach.We designed, fabricated, and tested a novel miniaturized TMS coil (4-by-7 mm) that consisted of a C-shaped iron powder core and insulated copper wires (30 turns). The resulting magnetic and electric fields were characterized with experimental measurements and finite element modeling. The efficacy of this coil in neuromodulation was validated with electrophysiological recordings of single-unit activities (SUAs), somatosensory evoked potentials (SSEPs), and motor evoked potentials (MEPs) in rats (n= 32) following repetitive TMS (rTMS; 3 min, 10 Hz).Main results.This coil could generate a maximum magnetic field of 460 mT and an electric field of 7.2 V m-1in the rat brain according to our simulations. With subthreshold rTMS focally delivered over the sensorimotor cortex, mean firing rates of primary somatosensory and motor cortical neurons significantly increased (154±5% and 160±9% from the baseline level, respectively); MEP and SSEP amplitude significantly increased (136±9%) and decreased (74±4%), respectively.Significance.This miniaturized C-shaped coil enabled focal TMS and concurrent electrophysiological recording/stimulation at the TMS focal point. It provided a useful tool to investigate the neural responses and underlying mechanisms of TMS in small animal models. Using this paradigm, we for the first time observed distinct modulatory effects on SUAs, SSEPs, and MEPs with the same rTMS protocol in anesthetized rats. These results suggested that multiple neurobiological mechanisms in the sensorimotor pathways were differentially modulated by rTMS.

What has neurophysiology revealed about migraine and chronic migraine?

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

Changes in somatosensory evoked potentials elicited by lateral cerebellar nucleus deep brain stimulation in the naïve rodent

Deep brain stimulation (DBS) of the deep cerebellar nuclei has been shown to enhance perilesional cortical excitability and promote motor rehabilitation in preclinical models of cortical ischemia and is currently being evaluated in patients with chronic, post-stroke deficits. Understanding the effects of cerebellar DBS on contralateral sensorimotor cortex may be key to developing approaches to optimize stimulation delivery and treatment outcomes. Using the naïve rat model, we characterized the effects of DBS of the lateral cerebellar nucleus (LCN) on somatosensory evoked potentials (SSEPs) and evaluated their potential use as a surrogate index of cortical excitability. SSEPs were recorded concurrently with continuous 30 Hz or 100 Hz LCN DBS and compared to the DBS OFF condition. Ratios of SSEP peak to peak amplitude during 100 Hz LCN DBS to DBS OFF at longer latency peaks were significantly>1, suggesting that cortical excitability was enhanced as a result of LCN DBS. Although changes in SSEP peak to peak amplitudes were observed, they were modest in relation to previously reported effects on motor cortical excitability. Overall, our findings suggest that LCN output influences thalamocortical somatosensory pathways, however further work is need to better understand the potential role of SSEPs in optimizing therapy.

Evidence Mapping Based on Systematic Reviews of Repetitive Transcranial Magnetic Stimulation on the Motor Cortex for Neuropathic Pain

BACKGROUND AND OBJECTIVE

There is vast published literature proposing repetitive transcranial magnetic stimulation (rTMS) technology on the motor cortex (M1) for the treatment of neuropathic pain (NP). Systematic reviews (SRs) focus on a specific problem and do not provide a comprehensive overview of a research area. This study aimed to summarize and analyze the evidence of rTMS on the M1 for NP treatment through a new synthesis method called evidence mapping.

METHODS

Searches were conducted in PubMed, EMBASE, Epistemonikos, and The Cochrane Library to identify the studies that summarized the effectiveness of rTMS for NP. The study type was restricted to SRs with or without meta-analysis. All literature published before January 23, 2021, was included. Two reviewers independently screened the literature, assessed the methodological quality, and extracted the data. The methodological quality of the included SRs was assessed by using the A Measurement Tool to Assess Systematic Reviews (AMSTAR-2). Data were extracted following a defined population, intervention, comparison, and outcome (PICO) framework from primary studies that included SRs. The same PICO was categorized into PICOs according to interventions [frequency, number of sessions (short: 1-5 sessions, medium: 5-10 sessions, and long: >10 sessions)] and compared. The evidence map was presented in tables and a bubble plot.

RESULTS

A total of 38 SRs met the eligibility criteria. After duplicate primary studies were removed, these reviews included 70 primary studies that met the scope of evidence mapping. According to the AMSTAR-2 assessment, the quality of the included SRs was critically low. Of these studies, 34 SRs scored "critically low" in terms of methodological quality, 2 SR scored "low," 1 SR scored "moderate," and 1 SR scored "high."

CONCLUSION

Evidence mapping is a useful methodology to provide a comprehensive and reliable overview of studies on rTMS for NP. Evidence mapping also shows that further investigations are necessary to highlight the optimal stimulation protocols and standardize all parameters to fill the evidence gaps of rTMS. Given that the methodological quality of most included SRs was "critically low," further investigations are advised to improve the methodological quality and the reporting process of SRs.

Neuromodulation for Chronic Daily Headache

Purpose of Review

We reviewed the literature that explored the use of central and peripheral neuromodulation techniques for chronic daily headache (CDH) treatment.

Recent Findings

Although the more invasive deep brain stimulation (DBS) is effective in chronic cluster headache (CCH), it should be reserved for extremely difficult-to-treat patients. Percutaneous occipital nerve stimulation has shown similar efficacy to DBS and is less risky in both CCH and chronic migraine (CM). Non-invasive transcutaneous vagus nerve stimulation is a promising add-on treatment for CCH but not for CM. Transcutaneous external trigeminal nerve stimulation may be effective in treating CM; however, it has not yet been tested for cluster headache. Transcranial magnetic and electric stimulations have promising preventive effects against CM and CCH.

Summary

Although the precise mode of action of non-invasive neuromodulation techniques remains largely unknown and there is a paucity of controlled trials, they should be preferred to more invasive techniques for treating CDH.

Treatment of Persistent Post-Concussion Syndrome with Repetitive Transcranial Magnetic Stimulation Using Functional Near-Infrared Spectroscopy as a Biomarker of Response: A Randomized Sham-Controlled Clinical Trial Protocol (Preprint)

Background

Approximately one-third of all concussions lead to persistent postconcussion syndrome (PPCS). Repetitive transcranial magnetic stimulation (rTMS) is a form of noninvasive brain stimulation that has been extensively used to treat refractory major depressive disorder and has a strong potential to be used as a treatment for patients with PPCS. Functional near-infrared spectroscopy (fNIRS) has already been used as a tool to assess patients with PPCS and may provide insight into the pathophysiology of rTMS treatment in patients with PPCS.

Objective

The primary objective of this research is to determine whether rTMS treatment improves symptom burden in patients with PPCS compared to sham treatment using the Rivermead postconcussion symptom questionnaire. The secondary objective is to explore the neuropathophysiological changes that occur following rTMS in participants with PPCS using fNIRS. Exploratory objectives include determining whether rTMS treatment in participants with PPCS will also improve quality of life, anxiety, depressive symptoms, cognition, posttraumatic stress, and function secondary to headaches.

Methods

A total of 44 adults (18-65 years old) with PPCS (>3 months to 5 years) will participate in a double-blind, sham-controlled, concealed allocation, randomized clinical trial. The participants will engage in either a 4-week rTMS treatment protocol or sham rTMS protocol (20 treatments). The left dorsolateral prefrontal cortex will be located through Montreal Neurologic Institute coordinates. The intensity of the rTMS treatment over the left dorsolateral prefrontal cortex will be 120% of resting motor threshold, with a frequency of 10 Hz, 10 trains of 60 pulses per train (total of 600 pulses), and intertrain interval of 45 seconds. Prior to starting the rTMS treatment, participant and injury characteristics, questionnaires (symptom burden, quality of life, depression, anxiety, cognition, and headache), and fNIRS assessment will be collected. Repeat questionnaires and fNIRS will occur immediately after rTMS treatment and at 1 month and 3 months post rTMS. Outcome parameters will be analyzed by a 2-way (treatment × time) mixed analysis of variance.

Results

As of May 6, 2021, 5 participants have been recruited for the study, and 3 have completed the rTMS protocol. The estimated completion date of the trial is May 2022.

Conclusions

This trial will expand our knowledge of how rTMS can be used as a treatment option of PPCS and will explore the neuropathophysiological response of rTMS through fNIRS analysis.

Trial Registration

ClinicalTrials.gov NCT04568369; https://clinicaltrials.gov/ct2/show/NCT04568369

International Registered Report Identifier (IRRID)

DERR1-10.2196/31308

Role of High Frequency Oscillations of Somatosensory Evoked Potentials in Deciphering Pathophysiology of Migraine

Background  Habituation deficit is considered as a neurophysiological abnormality among migraineurs in the interictal period. For clear comprehension and clarity about the mechanism underlying habituation in migraine, a sophisticated method, i.e., high frequency oscillations (HFOs) evoked potentials, have been utilized. However, studies pertaining to this in the Indian context are rare.

Objective  The aim of the study is to determine the utility of HFO of somatosensory evoked potential (SSEP) in deciphering the pathophysiology of migraine.

Materials and Methods  Sixty subjects including 30 migraineurs in the interictal period and 30 healthy controls were considered for the study. Median nerve SSEP was recorded in patients and controls by standard protocols. HFO was extracted offline using the Digital zero-phase shift band-pass filtering at 450 and 750 Hz. The early and late HFOs were determined with respect to the N20 peak and were compared between the groups.

Results  Of total 30 migraineurs, 18 had hemicranial headache and 12 had holocranial headache. N20 latency, P25 latency, N20 onset to peak amplitude, and N20 onset to P25 amplitude were comparable in migraineurs and controls. The intraburst frequency of early HFOs in migraineurs was significantly higher ( p = 0.04), whereas the peak-to-peak amplitude was significantly lower ( p = 0.001).

Conclusion  Early HFOs on SSEP represent the thalamocortical excitatory drive in migraineurs. Overall, the study reports that reduced amplitude of early HFOs in the interictal period suggest reduced thalamocortical drive in migraineurs.

Treatment of Persistent Post-Traumatic Headache and Post-Concussion Symptoms Using Repetitive Transcranial Magnetic Stimulation: A Pilot, Double-Blind, Randomized Controlled Trial

Persistent post-traumatic headache (PTH) after mild traumatic brain injury is one of the most prominent and highly reported persistent post-concussion symptoms (PPCS). Non-pharmacological treatments, including non-invasive neurostimulation technologies, have been proposed for use. Our objective was to evaluate headache characteristics at 1 month after repetitive transcranial magnetic stimulation (rTMS) treatment in participants with PTH and PPCS. A double-blind, randomized, sham-controlled, pilot clinical trial was performed on 20 participants (18-65 years) with persistent PTH (International Classification of Headache Disorders, 3rd edition) and PPCS (International Classification of Diseases, Tenth Revision). Ten sessions of rTMS therapy (10 Hz, 600 pulses, 70% resting motor threshold amplitude) were delivered to the left dorsolateral pre-frontal cortex. The primary outcome was a change in headache frequency or severity at 1 month post-rTMS. Two-week-long daily headache diaries and clinical questionnaires assessing function, PPCS, cognition, quality of life, and mood were completed at baseline, post-treatment, and at 1, 3, and 6 months post-rTMS. A two-way (treatment × time) mixed analyisis of variance indicated a significant overall time effect for average headache severity (F_(3,54) = 3.214; p = 0.03) and a reduction in headache frequency at 1 month post-treatment (#/2 weeks, REAL -5.2 [standard deviation {SD} = 5.8]; SHAM, -3.3 [SD = 7.7]). Secondary outcomes revealed an overall time interaction for headache impact, depression, post-concussion symptoms, and quality of life. There was a significant reduction in depression rating in the REAL group between baseline and 1 month post-treatment, with no change in the SHAM group (Personal Health Questionnaire-9; REAL, -4.3 [SD = 3.7[ p = 0.020]; SHAM, -0.7 [SD = 4.7; p = 1.0]; Bonferroni corrected). In the REAL group, 60% returned to work whereas only 10% returned in the SHAM group (p = 0.027). This pilot study demonstrates an overall time effect on headache severity, functional impact, depression, PPCS, and quality of life after rTMS treatment in participants with persistent PTH; however, findings were below clinical significance thresholds. There was a 100% response rate, no dropouts, and minimal adverse effects, warranting a larger phase II study. Clinicaltrials.gov: NCT03691272.

Treating Chronic Migraine With Neuromodulation: The Role of Neurophysiological Abnormalities and Maladaptive Plasticity

Chronic migraine (CM) is the most disabling form of migraine, because pharmacological treatments have low efficacy and cumbersome side effects. New evidence has shown that migraine is primarily a disorder of brain plasticity and migraine chronification depends on a maladaptive process favoring the development of a brain state of hyperexcitability. Due to the ability to induce plastic changes in the brain, researchers started to look at Non-Invasive Brain Stimulation (NIBS) as a possible therapeutic option in migraine field. On one side, NIBS techniques induce changes of neural plasticity that outlast the period of the stimulation (a fundamental prerequisite of a prophylactic migraine treatment, concurrently they allow targeting neurophysiological abnormalities that contribute to the transition from episodic to CM. The action may thus influence not only the cortex but also brainstem and diencephalic structures. Plus, NIBS is not burdened by serious medication side effects and drug–drug interactions. Although the majority of the studies reported somewhat beneficial effects in migraine patients, no standard intervention has been defined. This may be due to methodological differences regarding the used techniques (e.g., transcranial magnetic stimulation, transcranial direct current stimulation), the brain regions chosen as targets, and the stimulation types (e.g., the use of inhibitory and excitatory stimulations on the basis of opposite rationales), and an intrinsic variability of stimulation effect. Hence, it is difficult to draw a conclusion on the real effect of neuromodulation in migraine. In this article, we first will review the definition and mechanisms of brain plasticity, some neurophysiological hallmarks of migraine, and migraine chronification-related (dys)plasticity. Secondly, we will review available results from therapeutic and physiological studies using neuromodulation in CM. Lastly we will discuss the results obtained in these preventive trials in the light of a possible effect on brain plasticity.