Electroencephalogram (EEG) is widely available as a powerful mean to non-invasively study brain connectivity features in migraine patients. High density EEG, by means of a minimum of 64 up to 256 electrodes, enables to record electrical brain activity with high spatial resolution. Through the analysis of brain oscillations across different frequency bands (from alpha to delta), it can evaluate sensory, pain processing and information integration, contributing to a better definition of baseline features and to detect potential markers or predictors for therapeutic interventions in an era addressed to precision medicine.
Previous neurophysiological studies focused on EEG and to assess functional connectivity or spectral analysis in migraine patients. Conventional studies found higher slow wave activity (predominantly theta) in the interictal phase and higher excitability in the visual cortex during visual aura.
In 2016 a resting state study showed a predominance of low frequency bands in the ictal phase. The interictal and ictal phases patients also presented a diffuse lower coherence, suggesting low functional connectivity. Furthermore, an altered spatial connectivity for lower alpha-band activities was found in the interictal phases during sensory stimulation by means of HD-EEG, suggesting a thalamocortical dysrhythmia.
Nowadays, targeted preventive migraine therapies are available, namely monoclonal antibodies directed against the Calcitonin Gene Related Peptide (CGRP) pathway (mAbs). They demonstrated high efficacy and tolerability in both chronic and episodic migraine. Despite their peripheral site of action (outside of the blood brain barrier), the resulting action may take place at central level or determine clinical modifications leading to a functional modulation of several brain areas.
The primary aim of the study is to evaluate changes in functional connectivity in patients undergoing preventive mAbs treatment using HD- EEG and eventual connectivity differences between Responders and Non-Responders.
Study design:
Patients will undergo visits planned at baseline (T0) and quarterly (T3-T6) during which clinical data is collected and an HD-EEG is performed. Healthy controls will undergo EEG registration once.
HD-EEG registration:
The investigators will randomly acquire 4 recordings (6 minutes each) in resting-state condition, 2 with opened eyes, and 2 with closed eyes.
Resting state FC will be analyzed among six resting state networks (Default mode network, Dorsal attention network, Ventral attention network, Language network , Somatomotor network and Visual network) in the following frequency bands: alfa 8-12 Hz, beta 13-30 Hz, gamma 31-80 Hz, theta 4-7 Hz. delta 1-3 Hz.
Acquisition parameters will be: High-Pass: 0.5 Hz; Low-Pass: 100 Hz; Notch: 50 Hz. For analysis of HD-EEG data, the investigators will use a tailored analysis pipe-line that was previously developed and validated to reconstruct neural sources from cortical/subcortical gray matter. EEG signals will be band-pass filtered (1-80 Hz) and down-sampled at 250 Hz. Biological artifacts will be rejected using Independent Component Analysis (ICA). EEG signals will be referenced with a customized version of the Reference Electrode Standardization Technique (REST). A matrix will estimate the relationship between the measured scalp potentials and the dipoles corresponding to brain sources. Sources reconstruction will be performed with the exact low-resolution brain electromagnetic tomography (eLORETA) algorithm
Statistical plan:
The sample size was computed with the freeware online platform www.openepi.com. As few studies focused on functional connectivity evaluation in migraine, with no studies analyzing longitudinal changes during a specific treatment, the sample size analysis was based on the work of Bjork. The investigators thus considered as clinically meaningful a difference between groups in the theta relative power band equal to 0.04 (±0.04). Considering a two-tailed t-test for the comparison with confidence interval 95%; power: 80%, the minimum suggested sample size was 20 subjects for CM group and 20 subjects for HFEM group.
A preliminary normality analysis will be performed to decide whether to use parametric or non-parametric methods, through Shapiro Wilk test.
Numerical variables will be described as mean and standard deviation (or median and quartiles if appropriate), categorical variables as raw numbers and percentages.
Functional connectivity analyses will be conducted for separate bands and eyes closed registration.
