Lack of cold pressor test-induced effect on visual-evoked potentials in migraine

Visual Processing During the Interictal Period Between Migraines: A Meta-Analysis

Migraine is a poorly understood neurological disorder and a leading cause of disability in young adults, particularly women. Migraines are characterized by recurring episodes of severe pulsating unilateral headache and usually visual symptoms. Currently there is some disagreement in the electrophysiological literature regarding the universality of all migraineurs exhibiting physiological visual impairments also during interictal periods (i.e., the symptom free period between migraines). Thus, this meta-analysis investigated the evidence for altered visual function as measured electrophysiologically via pattern-reversal visual evoked potential (VEP) amplitudes and habituation in adult migraineurs with or without visual aura and controls in the interictal period. Twenty-three studies were selected for random effects meta-analysis which demonstrated slightly diminished VEP amplitudes in the early fast conducting P100 component but not in N135, and substantially reduced habituation in the P100 and the N135 in migraineurs with and without visual aura symptoms compared to controls. No statistical differences were found between migraineurs with and without aura, possibly due to inadequate studies. Overall, insufficient published data and substantial heterogeneity between studies was observed for all latency components of pattern-reversal VEP, highlighting the need for further electrophysiological experimentation and more targeted temporal analysis of visual function, in episodic migraineurs.

Exploring sensory sensitivity, cortical excitability, and habituation in episodic migraine, as a function of age and disease severity, using the pattern-reversal task

BACKGROUND

Migraine is a cyclic, neurosensory disorder characterized by recurrent headaches and altered sensory processing. The latter is manifested in hypersensitivity to visual stimuli, measured with questionnaires and sensory thresholds, as well as in abnormal cortical excitability and a lack of habituation, assessed with visual evoked potentials elicited by pattern-reversal stimulation. Here, the goal was to determine whether factors such as age and/or disease severity may exert a modulatory influence on sensory sensitivity, cortical excitability, and habituation.

METHODS

Two similar experiments were carried out, the first comparing 24 young, episodic migraine patients and 28 healthy age- and gender-matched controls and the second 36 middle-aged, episodic migraine patients and 30 healthy age- and gender-matched controls. A neurologist confirmed the diagnoses. Migraine phases were obtained using eDiaries. Sensory sensitivity was assessed with the Sensory Perception Quotient and group comparisons were carried out. We obtained pattern-reversal visual evoked potentials and calculated the N1-P1 Peak-to-Peak amplitude. Two linear mixed-effects models were fitted to these data. The first model had Block (first block, last block) and Group (patients, controls) as fixed factors, whereas the second model had Trial (all trials) and Group as fixed factors. Participant was included as a random factor in both. N1-P1 first block amplitude was used to assess cortical excitability and habituation was defined as a decrease of N1-P1 amplitude across Blocks/Trials. Both experiments were performed interictally.

RESULTS

The final samples consisted of 18 patients with episodic migraine and 27 headache-free controls (first experiment) and 19 patients and 29 controls (second experiment). In both experiments, patients reported increased visual hypersensitivity on the Sensory Perception Quotient as compared to controls. Regarding N1-P1 peak-to-peak data, there was no main effect of Group, indicating no differences in cortical excitability between groups. Finally, significant main effects of both Block and Trial were found indicating habituation in both groups, regardless of age and headache frequency.

CONCLUSIONS

The results of this study yielded evidence for significant hypersensitivity in patients but no significant differences in either habituation or cortical excitability, as compared to headache-free controls. Although the alterations in patients may be less pronounced than originally anticipated they demonstrate the need for the definition and standardization of optimal methodological parameters.

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.

Impaired short-term visual paired associative plasticity in patients with migraine between attacks

ABSTRACT

A common experimental neurophysiological method to study synaptic plasticity is pairing activity of somatosensory afferents and motor cortical circuits, so-called paired associative stimulation (PAS). Dysfunctional inhibitory and excitatory PAS mechanisms within the sensorimotor system were described in patients with migraine without aura (MO) between attacks. We have recently observed that the same bidirectional PAS rules also apply to the visual system. Here, we have tested whether dysfunctioning associative plasticity might characterize the visual system of patients with MO. In 14 patients with MO between attacks and in 15 healthy volunteers, we performed a previously validated visual PAS (vPAS) protocol by coupling 90 black-and-white checkerboard reversals with low-frequency transcranial magnetic stimulation pulses over the occipital cortex at 2 interstimulus intervals of -25/+25 ms around the visual-evoked potential (VEP) P1 latency. We recorded VEPs (600 sweeps) before, immediately after, and 10 min after each vPAS session. We analysed VEP N1-P1 amplitude and delayed habituation. Although vPAS-25 significantly enhanced and vPAS + 25 reduced VEP amplitude habituation in healthy volunteers, the same protocols did not significantly change VEP amplitude habituation in MO between attacks. We provide evidence for lack of habituation enhancing and habituation suppressing visual PAS mechanisms within the visual system in interictal migraine. This finding, in combination with those previously obtained studying the sensorimotor system, leads us to argue that migraine disease-related dysrhythmic thalamocortical activity prevents the occurrence of physiological bidirectional synaptic plasticity induced by vPAS.

Visual Evoked Potential Responses after Photostress in Migraine Patients and Their Correlations with Clinical Features

In the past few years, researchers have detected subtle macular vision abnormalities using different psychophysical experimental tasks in patients with migraine. Recording of visual evoked potential (VEP) after photostress (PS) represents an objective way to verify the integrity of the dynamic properties of macular performance after exposure to intense light. VEPs were recorded before and after PS in 51 patients with migraine (19 with aura (MA) and 22 without aura (MO) between attacks, and 10 recorded during an attack (MI)) and 14 healthy volunteers. All study participants were exposed to 30 s of PS through the use of a 200-watt bulb lamp. The P100 implicit time and N75-P100 amplitude of the baseline VEP were compared with those collected every 20 s up to 200 s after PS. VEP parameters recorded at baseline did not differ between groups. In all groups, the VEP recordings exhibited a significant increase in implicit times and a reduction in amplitude at 20 s after the PS. In migraine, the percentage decrease in amplitudes observed at 20 s after photostress was significantly lower than in healthy volunteers, in both MO and MA patients, but not in MI patients. When data for MO and MA patients were combined, the percentage of amplitude change at 20 s was negatively correlated with the number of days that had elapsed since the last migraine attack, and positive correlated with attack frequency. We showed dynamic changes of recovery of VEP after PS depending on the migraine cycle. This finding, in conjunction with those previously attained with other neuromodulatory interventions using VEPs, leads us to argue that migraine-disease-related dysrhythmic thalamocortical activity precludes amplitude suppression by PS.

Migraine and cluster headache - the common link

Although clinically distinguishable, migraine and cluster headache share prominent features such as unilateral pain, common pharmacological triggers such glyceryl trinitrate, histamine, calcitonin gene-related peptide (CGRP) and response to triptans and neuromodulation. Recent data also suggest efficacy of anti CGRP monoclonal antibodies in both migraine and cluster headache. While exact mechanisms behind both disorders remain to be fully understood, the trigeminovascular system represents one possible common pathophysiological pathway and network of both disorders. Here, we review past and current literature shedding light on similarities and differences in phenotype, heritability, pathophysiology, imaging findings and treatment options of migraine and cluster headache. A continued focus on their shared pathophysiological pathways may be important in paving future treatment avenues that could benefit both migraine and cluster headache patients.

The cold pressor test in interictal migraine patients - different parasympathetic pupillary response indicates dysbalance of the cranial autonomic nervous system

Background

Data on autonomic nervous system (ANS) activations in migraine patients are quite controversial, with previous studies reporting over- and underactivation of the sympathetic as well as parasympathetic nervous system. In the present study, we explicitly aimed to assess the cranial ANS in migraine patients compared to healthy controls by applying the cold pressor test to a cohort of migraine patients in the interictal phase and measuring the pupillary response.

Methods

In this prospective observational study, a strong sympathetic stimulus was applied to 20 patients with episodic migraine in the interictal phase and 20 matched controls without migraine, whereby each participant dipped the left hand into ice-cold (4 °C) water for a maximum of 5 min (cold pressor test). At baseline, 2, and 5 min during the cold pressor test, infrared monocular pupillometry was applied to quantify pupil diameter and light reflex parameters. Simultaneously, heart rate and blood pressure were measured by the external brachial RR-method at distinct time intervals to look for at least clinically relevant changes of the cardiovascular ANS.

Results

There were no significant differences between the migraine patients and controls at baseline and after 2 min of sympathetic stimulation in all the measured pupillary and cardio-vascular parameters. However, at 5 min, pupillary light reflex (PLR) constriction velocity was significantly higher in migraineurs than in controls (5.59 ± 0.73 mm/s vs. 5.16 ± 0.53 mm/s; unpaired t-test p < 0.05), while both cardiovascular parameters and PLR dilatation velocity were similar in both groups at this time point.

Conclusions

Our findings of an increased PLR constriction velocity after sustained sympathetic stimulation in interictal migraine patients suggest an exaggerated parasympathetic response of the cranial ANS. This indicates that brainstem parasympathetic dysregulation might play a significant role in migraine pathophysiology. More dedicated examination of the ANS in migraine patients might be of value for a deeper understanding of its pathophysiology.

Electronic supplementary material

The online version of this article (10.1186/s12883-018-1043-2) contains supplementary material, which is available to authorized users.

Sunlight irradiance and habituation of visual evoked potentials in migraine: The environment makes its mark

Background Migraine is a complex multifactorial disease that arises from the interaction between a genetic predisposition and an enabling environment. Habituation is considered as a fundamental adaptive behaviour of the nervous system that is often impaired in migraine populations. Given that migraineurs are hypersensitive to light, and that light deprivation is able to induce functional changes in the visual cortex recognizable through visual evoked potentials habituation testing, we hypothesized that regional sunlight irradiance levels could influence the results of visual evoked potentials habituation studies performed in different locations worldwide. Methods We searched the literature for visual evoked potentials habituation studies comparing healthy volunteers and episodic migraine patients and correlated their results with levels of local solar radiation. Results After reviewing the literature, 26 studies involving 1291 participants matched our inclusion criteria. Deficient visual evoked potentials habituation in episodic migraine patients was reported in 19 studies. Mean yearly sunlight irradiance was significantly higher in locations of studies reporting deficient habituation. Correlation analyses suggested that visual evoked potentials habituation decreases with increasing sunlight irradiance in migraine without aura patients. Conclusion Results from this hypothesis generating analysis suggest that variations in sunlight irradiance may induce adaptive modifications in visual processing systems that could be reflected in visual evoked potentials habituation, and thus partially account for the difference in results between studies performed in geographically distant centers. Other causal factors such as genetic differences could also play a role, and therefore well-designed prospective trials are warranted.

Impaired brainstem and thalamic high-frequency oscillatory EEG activity in migraine between attacks

Introduction

We investigated whether interictal thalamic dysfunction in migraine without aura (MO) patients is a primary determinant or the expression of its functional disconnection from proximal or distal areas along the somatosensory pathway.

Methods

Twenty MO patients and twenty healthy volunteers (HVs) underwent an electroencephalographic (EEG) recording during electrical stimulation of the median nerve at the wrist. We used the functional source separation algorithm to extract four functionally constrained nodes (brainstem, thalamus, primary sensory radial, and primary sensory motor tangential parietal sources) along the somatosensory pathway. Two digital filters (1–400 Hz and 450–750 Hz) were applied in order to extract low- (LFO) and high- frequency (HFO) oscillatory activity from the broadband signal.

Results

Compared to HVs, patients presented significantly lower brainstem (BS) and thalamic (Th) HFO activation bilaterally. No difference between the two cortical HFO as well as in LFO peak activations between the two groups was seen. The age of onset of the headache was positively correlated with HFO power in the right brainstem and thalamus.

Conclusions

This study provides evidence for complex dysfunction of brainstem and thalamocortical networks under the control of genetic factors that might act by modulating the severity of migraine phenotype.

Lateral inhibition in the somatosensory cortex during and between migraine without aura attacks: Correlations with thalamocortical activity and clinical features

Background

We studied lateral inhibition in the somatosensory cortex of migraineurs during and between attacks, and searched for correlations with thalamocortical activity and clinical features.

Participants and methods

Somatosensory evoked potentials (SSEP) were obtained by electrical stimulation of the right median (M) or ulnar (U) nerves at the wrist or by simultaneous stimulation of both nerves (MU) in 41 migraine without aura patients, 24 between (MO), 17 during attacks, and in 17 healthy volunteers (HVs). We determined the percentage of lateral inhibition of the N20–P25 component by using the formula [(100)–MU/(M + U)*100]. We also studied high-frequency oscillations (HFOs) reflecting thalamocortical activation.

Results

In migraine, both lateral inhibition (MO 27.9% vs HVs 40.2%; p = 0.009) and thalamocortical activity (MO 0.5 vs HVs 0.7; p = 0.02) were reduced between attacks, but not during. In MO patients, the percentage of lateral inhibition negatively correlated with days elapsed since the last migraine attack ( r = −0.510, p = 0.01), monthly attack duration ( r = −0.469, p = 0.02) and severity ( r = −0.443, p = 0.03), but positively with thalamocortical activity ( r = −0.463, p = 0.02).

Conclusions

We hypothesize that abnormal migraine cycle-dependent dynamics of connectivity between subcortical and cortical excitation/inhibition networks may contribute to clinical features of MO and recurrence of attacks.

Auditory stimulation enhances thalamic somatosensory high-frequency oscillations in healthy humans: a neurophysiological marker of cross-sensory sensitization?

Electrical stimulation of upper limb nerves evokes a train of high-frequency wavelets (high-frequency oscillations, HFOs) on the human scalp. These HFOs are related to the influence of arousal-promoting structures on somatosensory input processing, and are generated in the primary somatosensory cortex (post-synaptic HFOs) and the terminal tracts of thalamocortical radiations (pre-synaptic HFOs). We previously reported that HFOs do not undergo habituation to repeated stimulations; here, we verified whether HFOs could be modulated by external sensitizing stimuli. We recorded somatosensory evoked potentials (SSEPs) in 15 healthy volunteers before and after sensitization training with an auditory stimulus. Pre-synaptic HFO amplitudes, reflecting somatosensory thalamic/thalamocortical activity, significantly increased after the sensitizing acoustic stimulation, whereas both the low-frequency N20 SSEP component and post-synaptic HFOs were unaffected. Cross-talk between subcortical arousal-related structures is a probable mechanism for the pre-synaptic HFO effect observed in this study. We propose that part of the ascending somatosensory input encoded in HFOs is specifically able to convey sensitized inputs. This preferential involvement in sensitization mechanisms suggests that HFOs play a critical role in the detection of potentially relevant stimuli, and act at very early stages of somatosensory input processing.

Study of neurovascular coupling during cold pressor test in patients with migraine

BACKGROUND

Altered neurovascular coupling in migraineurs could be a consequence of impaired function of modulatory brainstem nuclei. The cold pressor test (CPT) should activate brainstem structures. We measured visually evoked cerebral blood flow velocity response (VEFR) to CPT in migraine.

METHODS

Twenty-three healthy volunteers and 29 migraineurs participated in the study. We measured arterial blood pressure, end-tidal CO2, heart rate and cerebral blood flow velocity in posterior and middle cerebral artery using transcranial Doppler. VEFR was calculated as cerebrovascular reactivity to photic stimulation before, during and after CPT.

RESULTS

In healthy individuals, there was a significant decrease in peak systolic VEFR from CPT phase to recovery phase (p < 0.05). There was an increase in mean VEFR from basal to CPT phase and a decrease from CPT to recovery phase, both significant (p < 0.05). End-diastolic VEFR increased from basal to CPT phase and decreased in recovery phase below the basal phase values, all changes significant (p < 0.05). In migraine, no statistically significant changes in peak systolic, mean or end-diastolic VEFRs were observed between phases (p > 0.05). The differences in phases in mean and end-diastolic VEFRs between the basal phase and the CPT phase and between the CPT phase and the recovery phase were significantly higher in healthy individuals (p < 0.05).

CONCLUSIONS

The absence of the effect of CPT on VEFR in migraine is likely to be a consequence of impaired subcortical modulation of neurovascular coupling.

Habituation and sensitization in primary headaches

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

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.

Effects of light deprivation on visual evoked potentials in migraine without aura

Background

The mechanisms underlying the interictal habituation deficit of cortical visual evoked potentials (VEP) in migraine are not well understood. Abnormal long-term functional plasticity of the visual cortex may play a role and it can be assessed experimentally by light deprivation (LD).

Methods

We have compared the effects of LD on VEP in migraine patients without aura between attacks (MO, n = 17) and in healthy volunteers (HV, n = 17). Six sequential blocks of 100 averaged VEP at 3.1 Hz were recorded before and after 1 hour of LD. We measured VEP P100 amplitude of the 1^st block of 100 sweeps and its change over 5 sequential blocks of 100 responses.

Results

In HV, the consequence of LD was a reduction of 1^st block VEP amplitude and of the normal habituation pattern. By contrast, in MO patients, the interictal habituation deficit was not significantly modified, although 1^st block VEP amplitude, already lower than in HV before LD, further decreased after LD.

Conclusions

Light deprivation is thought to decrease both excitatory and subsequent inhibitory processes in visual cortex, which is in line with our findings in healthy volunteers. The VEP results in migraine patients suggest that early excitation was adequately suppressed, but not the inhibitory mechanisms occurring during long term stimulation and habituation. Accordingly, deficient intracortical inhibition is unlikely to be a primary factor in migraine pathophysiology and the habituation deficit.

Changes in visual-evoked potential habituation induced by hyperventilation in migraine

Hyperventilation is often associated with stress, an established trigger factor for migraine. Between attacks, migraine is associated with a deficit in habituation to visual-evoked potentials (VEP) that worsens just before the attack. Hyperventilation slows electroencephalographic (EEG) activity and decreases the functional response in the occipital cortex during visual stimulation. The neural mechanisms underlying deficient-evoked potential habituation in migraineurs remain unclear. To find out whether hyperventilation alters VEP habituation, we recorded VEPs before and after experimentally induced hyperventilation lasting 3 min in 18 healthy subjects and 18 migraine patients between attacks. We measured VEP P100 amplitudes in six sequential blocks of 100 sweeps and habituation as the change in amplitude over the six blocks. In healthy subjects, hyperventilation decreased VEP amplitude in block 1 and abolished the normal VEP habituation. In migraine patients, hyperventilation further decreased the already low block 1 amplitude and worsened the interictal habituation deficit. Hyperventilation worsens the habituation deficit in migraineurs possibly by increasing dysrhythmia in the brainstem-thalamo-cortical network.