Changes in Cortical Dynamics in the Preictal Stage of a Migraine Attack

Neurophysiological and Clinical Outcomes in Episodic Migraine Without Aura: A Cross-Sectional Study

PURPOSE

The aim of this study was to assess differences between people with episodic migraine and healthy controls in some neurophysiological and clinical outcomes, which, in turn, may highlight the differences in sensory processing, especially in cortical excitability, pain processing, and executive function.

METHODS

A cross-sectional study was performed, including the following outcomes: pressure pain thresholds with algometry; resting motor threshold, short-interval intracortical inhibition, and intracortical facilitation with transcranial magnetic stimulation; and executive functions with the trail making test and the frontal assessment battery.

RESULTS

Thirty adults with migraine (36 ± 10 years) and 30 healthy controls (29 ± 14 years) were included in this study. Compared with the healthy controls, participants with migraine presented lower pressure pain thresholds values in all the assessed muscles ( P < 0.001), lower resting motor threshold (-10.5% of the stimulator output, 95% CI: -16.8 to -4.2, P = 0.001, Cohen d = 0.869) and higher short-interval intracortical inhibition motor-evoked potential's amplitude at 3 ms (0.25, 95% CI: 0.05 to 0.46, P = 0.015, Cohen d = 0.662), and worse performances both in trail making test (7.1, 95% CI: 0.9 to 13.4, P = 0.027, Cohen d = 0.594) and frontal assessment battery (-1.1, 95% CI: -1.7 to -0.5, P = 0.001, Cohen d = 0.915).

CONCLUSIONS

Participants with migraine presented significant differences in cortical excitability, executive functions, and pressure pain thresholds, compared with healthy controls.

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.

Fluctuations of sensorimotor processing in migraine: a controlled longitudinal study of beta event related desynchronization

Background

The migraine brain seems to undergo cyclic fluctuations of sensory processing. For instance, during the preictal phase, migraineurs experience symptoms and signs of altered pain perception as well as other well-known premonitory CNS-symptoms. In the present study we measured EEG-activation to non-painful motor and sensorimotor tasks in the different phases of the migraine cycle by longitudinal measurements of beta event related desynchronization (beta-ERD).

Methods

We recorded electroencephalography (EEG) of 41 migraine patients and 31 healthy controls. Each subject underwent three EEG recordings on three different days with classification of each EEG recording according to the actual migraine phase. During each recording, subjects performed one motor and one sensorimotor task with the flexion-extension movement of the right wrist.

Results

Migraine patients had significantly increased beta-ERD and higher baseline beta power at the contralateral C3 electrode overlying the primary sensorimotor cortex in the preictal phase compared to the interictal phase. We found no significant differences in beta-ERD or baseline beta power between interictal migraineurs and controls.

Conclusion

Increased preictal baseline beta activity may reflect a decrease in pre-activation in the sensorimotor cortex. Altered pre-activation may lead to changes in thresholds for inhibitory responses and increased beta-ERD response, possibly reflecting a generally increased preictal cortical responsivity in migraine. Cyclic fluctuations in the activity of second- and third-order afferent somatosensory neurons, and their associated cortical and/or thalamic interneurons, may accordingly also be a central part of the migraine pathophysiology.

Does pain sensitivity change by migraine phase? A blinded longitudinal study

Objective

Studies suggest that pain thresholds may be altered before and during migraine headaches, but it is still debated if a central or peripheral dysfunction is responsible for the onset of pain in migraine. The present blinded longitudinal study explores alterations in thermal pain thresholds and suprathreshold heat pain scores before, during, and after headache.

Methods

We measured pain thresholds to cold and heat, and pain scores to 30 seconds of suprathreshold heat four times in 49 migraineurs and once in 31 controls. Sessions in migraineurs were categorized by migraine diaries as interictal, preictal (≤one day before attack), ictal or postictal (≤one day after attack).

Results

Trigeminal cold pain thresholds were decreased ( p = 0.014) and pain scores increased ( p = 0.031) in the ictal compared to the interictal phase. Initial pain scores were decreased ( p < 0.029), and the temporal profile showed less adaptation ( p < 0.020) in the preictal compared to the interictal phase. Hand cold pain thresholds were decreased in interictal migraineurs compared to controls ( p < 0.019).

Conclusion

Preictal heat hypoalgesia and reduced adaptation was followed by ictal trigeminal cold suballodynia and heat hyperalgesia. Our results support that cyclic alterations of pain perception occur late in the prodromal phase before headache. Further longitudinal investigation of how pain physiology changes within the migraine cycle is important to gain a more complete understanding of the pathogenic mechanisms behind the migraine attack.

What initiates a migraine attack? Conclusions from four longitudinal studies of quantitative EEG and steady-state visual-evoked potentials in migraineurs

OBJECTIVES

Quantitative electroencephalograpic (QEEG) frequency spectra and steady-state visual-evoked potentials (SSVEP) are indicators of corticothalamic excitability (e.g., arousal). Increased interictal excitability is suggested to be an important element in the migraine pathophysiology. In this paper, we summarize our results from four studies of QEEG and SSVEP recordings in migraineurs interictally and in the days before an attack with the intention to shed light on attack-initiating mechanisms.

MATERIAL AND METHODS

Thirty-two healthy controls, 33 migraineurs without and eight with aura each had three EEGs with photic stimulation on different days. Using the patient headache diaries, we classified the recordings as interictal, preictal, ictal, or post-ictal retrospectively. Interictal recordings were compared pairwise with attack-related EEGs from the same patient as well as with control EEGs. We also correlated clinical variables with the QEEG and SSVEP data.

RESULTS

Between attacks, we found increased relative theta activity and attenuated medium-frequency photic responses in migraineurs without aura compared with those in controls. Within 36 h before the attack, slow and asymmetric EEG activity developed. Increased trigger sensitivity and photophobia correlated with higher theta power and depressed photic responses. Attack duration, migraine history duration, and pain intensity were associated with EEG slowing.

CONCLUSIONS

A general tendency toward EEG slowing and depression of photic responses characterized the migraine group. This pattern was also related to increased severity of symptoms. A change in cortical activity occurred within 36 h before attacks. Our results indicate that thalamocortical hypoexcitability is associated with attack initiation and sensory hypersensitivity in migraine.

Photic EEG-driving responses related to ictal phases and trigger sensitivity in migraine: a longitudinal, controlled study

INTRODUCTION

Photic driving is believed to be increased in migraineurs and has been interpreted as a sign of cortical hyperexcitability. However, most previous studies have included patients in various phases of the migraine cycle. The results are, therefore, difficult to interpret as neurophysiological abnormalities tend to accumulate close to the attack in migraineurs.

SUBJECTS AND METHODS

We recorded steady state visual evoked EEG-responses (SSVEPs) for 6, 12, 18 and 24 Hz flash stimuli from 33 migraineurs without aura, eight migraineurs with aura and 32 healthy controls. Interictal recordings were compared pair-wise with recordings before, during and after attack, as well as with EEGs from healthy controls. Driving power was also correlated with sensory hypersensitivity and severity of migraine.

RESULTS

Between attacks, driving responses to 18 Hz and 24 Hz were attenuated in migraineurs without aura. Driving power of 12 Hz increased before the attack. Attack trigger sensitivity, photophobia, pain intensity and a family history of migraine were related to decreased and/or symmetric photic driving.

CONCLUSIONS

Earlier results may have overestimated the driving response in migraine due to inclusion of recordings during the preictal interval and/or habituation among controls. Abnormal photic driving may be related to the pathophysiology of clinical sensory hypersensitivity.

Interictal quantitative EEG in migraine: a blinded controlled study

Abnormal electroencephalography (EEG) in migraineurs has been reported in several studies. However, few have evaluated EEG findings in migraineurs during a time period when neither the last attack nor the next attack may interact with the results. We, therefore, compared interictal EEG in migraineurs and headache-free subjects with a design controlled for interference by pre-ictal changes. Pre-ictal EEG findings in the painful cranial side during the next attack after registration were also investigated. Correlations between clinical variables and EEG are reported as well. Interictal EEGs from 33 migraineurs (6 with and 27 without aura) and 31 controls were compared. Absolute power, asymmetry and relative power were studied for delta, theta and alpha frequency bands in parieto-occipital, temporal and fronto-central areas. EEG variables were correlated to attack frequency, headache duration, attack duration, pain intensity, photo- and phonophobia. Compared with controls, migraineurs had increased relative theta power in all cortical regions and increased delta activity in the painful fronto-central region. Absolute power and asymmetry were similar among groups. In age-adjusted analyses, headache intensity correlated with increased delta activity. In this blinded controlled study, we found globally increased relative theta activity in migraineurs. A slight interictal brain dysfunction is probably present between attacks.

Quantitative EEG Power and Asymmetry Increase 36 h Before a Migraine Attack

The aim was to estimate ictal, pre- and postictal brain function changes in migraine in a blinded paired quantitative EEG (QEEG) study. EEG recordings ( n = 119) from 40 migraineurs were retrospectively classified as ictal, interictal, preictal or postictal. δ, θ, α and β power, and hemispheric asymmetry in frontocentral, temporal and occipitoparietal regions were calculated from artefact-free EEG. Power and power asymmetry were calculated for two time-windows, 36 and 72 h before/after the attack, and compared with the interictal values. Frontocentral δ power increased ( P = 0.03), whereas frontocentral θ and α power tended to increase ( P < 0.09) within 36 h before the next attack compared with the interictal period. Occipitoparietal (α and θ) and temporal (α) power were more asymmetric before the attack compared with the interictal baseline ( P < 0.04). Ictal posterior a power increased slightly ( P = 0.01). Postictal power and power asymmetry were not significantly different from interictal baseline. EEG activity seems to change shortly before the attack. This suggests that migraineurs are most susceptible to attack when anterior QEEG δ power and posterior α and θ asymmetry values are high. Changed activity patterns in cholinergic brainstem or basal forebrain nuclei and thalamo-cortical connections before the migraine attack are hypothesized.

Progress in predicting seizure episodes with nonlinear methods

One of the most interesting and significant areas of epileptology has been the prediction of the onset of a seizure episode from preictal activity with nonlinear methods. Not only does this type of study have heuristic value for clinical neurophysiology, but it also has potential utilitarian value for the patient with seizures. In this review, 47 reports from 12 centers with multiple studies are presented in chronological order, as are single reports from 21 other centers. The chronological order was chosen to see if progress in the form of earlier prediction was made over time. Only 21% of these reports could provide specific times for the prediction of seizure onset. The range of values was several minutes to 4 hours, with an average (median) of 6-7 minutes. Some reports (16%) had negative or nonspecific findings that prediction times could not be provided. Thus, only limited progress has been made in predicting a seizure from preictal activity, but many other related phenomena have also been studied with nonlinear methods with some success.

Effects of short- and long-term pulsed radiofrequency electromagnetic fields on night sleep and cognitive functions in healthy subjects

There has been wide public discussion on whether the electromagnetic fields of mobile telephones and their base stations affect human sleep or cognitive functioning. As there is evidence for learning and memory-consolidating effects of sleep and particularly of REM sleep, disturbance of sleep by radiofrequency electromagnetic fields might also impair cognitive functions. Previously realized sleep studies yielded inconsistent results regarding short-term exposure. Moreover, data are lacking on the effect that short- and long-term exposure might have on sleep as well as on cognitive functions. Therefore, 10 healthy young male subjects were included and nocturnal sleep was recorded during eight consecutive nights. In the second, third, and last night, we investigated polysomnographic night sleep and cognitive functions. After the adaptation and baseline nights, the participants were exposed to a defined radiofrequency electromagnetic field during the following six nights. We analyzed polysomnographic night sleep according to Rechtschaffen and Kales [1968, Manual of Standardized Terminology, Techniques and Scoring System for Sleep of Human Subjects] as well as by power spectra and correlation dimension. Cognitive functions were investigated by an array of neuropsychological tests. Data analysis was done by comparing the baseline night with the first and last exposure night and the first two sleep cycles of the respective nights. We did not find significant effects, either on conventional sleep parameters or on power spectra and correlation dimension, nor were there any significant effects on cognitive functions. With our results, we are unable to reveal either short-term or cumulative long-term effects of radiofrequency electromagnetic fields on night sleep and cognitive functions in healthy young male subjects.