Participants
Twenty-six patients with eCH (ICHD III code 3.1.1) and strictly unilateral pain attending the Headache Centers of Rome (directed by Prof. Vittorio Di Piero) and Latina (directed by Prof. Gianluca Coppola) were recruited. Patients were scanned during the in-bouts period outside of the attacks. Other primary or secondary headache types were excluded by clinical and/or instrumental evaluation, as appropriate. We collected information on various patient clinical characteristics at the time of either the screening visit or the day of the scanning session, including daily attack frequency, mean severity of headache attacks (0–10), duration of the attacks (hours), and duration of history of eCH (years). The exclusion criteria were severe systemic or neurological/neuro-ophthalmological diseases or psychiatric disorders. Patients with eCH and a family history of migraine (1st -degree relatives) were also excluded. No preventive drugs were permitted during the 3 months preceding the observations in eCH. For comparison, 20 healthy controls (HCs) of comparable age and sex distributions were recruited from among medical students and healthcare professionals. They were devoid of any overt medical conditions, personal or family history of primary headaches or epilepsy, or regular drug intake.
None of the enrolled participants experienced sleep deprivation or alcohol ingestion on the day preceding the recordings. Caffeinated beverages were not allowed on the day of the recording. All the participants provided written informed consent to participate in the study, which was approved by the local ethics committee (N° 0295/2023). The study complied with the principles of the Declaration of Helsinki for Human Experimentation.
fMRI data acquisition and preprocessing
MRI data were obtained using a Siemens 3T Verio scanner with a 12-channel head coil. Structural anatomic scans were performed using a T1-weighted sagittal magnetization-prepared rapid gradient echo (MPRAGE) series (TR: 1900 ms, TE: 2.93 ms, 176 sagittal slices, 0.508 × 0.508 × 1 mm3 voxels). We acquired an interleaved double-echo Turbo Spin Echo sequence proton density and T2-weighted images (repetition time: 3320ms, echo time: 10/103ms, matrix: 384 × 384, field of view: 220 mm, slice thickness: 4 mm, gap: 1.2 mm, 50 axial slices). fMRI data were obtained using T2*-weighted echo-planar imaging (TR, 3000 ms; TE, 30 ms; 40 axial slices, 3.906 × 3.906 × 3 mm; 150 volumes). Functional resting scans lasted for 7 min and 30 s. During these sessions, the participants were instructed to relax, avoid motion, and keep their eyes closed, but not fall asleep.
Data pre-processing was performed using SPM12 software (http://www.fil.ion.ucl.ac.uk/spm/) implemented in MATLAB (version R2016b, MathWorks, Inc., Natick, MA, USA). The data were realigned to the first volume to correct for head motion using a 6-parameter rigid body process and resliced using cubic spline interpolation. Moreover, in order to check motion, we calculated framewise displacement (FD), based on partecipants’ root mean square values (RMS) [14], their contrast was not statistically significant (0.0323 ± 0.0374, 0.0484 ± 0.333, p = 0.86 unpaired 2-sample t-test).
Structural (T1–MPRAGE) and functional data were co-registered for each participant. The normalization procedure transformed the structural and realigned EPI images into a standard stereotactic space based on Talairach and Tournoux [15], which was resampled 3 mm in each direction.
Finally, the normalized functional images were smoothed isotropically with a Gaussian kernel of 8 mm full width at half maximum.
DTI images were obtained with a single-shot echo-planar image sequence with the following parameters: repetition time (TR) = 12200 ms, echo time (TE) = 94 ms, field of view (FOV) = 192 mm x 192 mm, matrix = 96 x 96, 2 mm x 2 mm in-plane resolution, slice thickness = 2 mm, 72 continuous axial slices with no gap, 1 volume anterior to posterior (AP) phase of encoding direction b = 0 s/mm2, b = 1000 s/mm2, and 30 diffusion directions were isotropically distributed on a sphere where one direction lacked diffusion weighting resulting in 30 volumes of the AP phase of encoding direction and 1 volume posterior to anterior (PA) phase of encoding direction b = 0.
fMRI data analysis
Resting-state images were analyzed using spatial independent component analysis (ICA) with the infomax algorithm, which was implemented in the Group ICA of the fMRI Toolbox (GIFT- https://fsl.fmrib.ox.ac.uk/fsl).
Two data reduction steps were performed using the PCA: participant-specific and group-level steps.
First, the participant-specific data were reduced to 50 components and the participant-reduced data were concatenated across time. Secondly, at the group level, data were reduced to 20 group-independent components (ICs) using the expectation-maximization algorithm included in GIFT [16].
Two separate group spatial ICAs were also performed in the HCs and patients to ensure that the resulting components had similar resting-state fluctuations in the two groups, that is the resulting components obtained from all 46 participants combined.
The number of ICs was estimated using the minimum description length (MDL) criterion [17]. participant-specific spatial maps and time courses were obtained using the back-reconstruction approach (GICA) [18].
An expert neuroradiologist FC analyzed all group ICs identifying the RSNs [19, 20], omitting those located in the CSF, white matter, or with low correlation to gray matter because they can be artifacts, such as eye movements, head motion, or ballistic artifacts.
Indeed, we obtained eight functional networks: visuospatial (IC1), default mode network (DMN, IC3), executive control (ECN, IC5), salience (SN, IC7), ECN right and left (IC10 & IC12), DMN (IC16, ventral part), and medial visual (IC19) to be processed in the following step.
The Functional Network Toolbox (FNC; http://trendscenter.org/software/gift/) was used to evaluate whether there were different correlations between the groups’ networks.
Bandpass filter values were set between 0.033 Hz and 0.13 Hz.
DTI
Before pre-processing, all DTI volumes were visually inspected to screen for noisy artifacts due to cardiac pulsations, signal dropout, and motion artifacts.
Functional MRI of the Brain (FMRIB) Software Library (FSL version 6.0.6, https://fsl.fmrib.ox.ac.uk/fsl) was used to image data process [21–23].
First, the following FSL steps use the b = 0 volume AP and PA phase-encoding directions as references. The top-up tool estimates [24] and corrects [21] susceptibility-induced distortions, and the brain extraction tool (BET) creates brain masks from b = 0 volumes [25]. Eddy currents and movements were corrected using the Eddy tool.
Before the final step, the MRI-processed images were assessed using a quality control framework [26].
The DTIFIT toolbox fits the preprocessed images based on a diffusion tensor model to yield the fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD).
The hypothalamic and thalamic ROIs were defined using FSL and registered as MRI diffusion images using algorithms embedded in the FDT toolbox [27, 28].
Statistical analysis
Group differences in demographic data were estimated using SPSS version 23 (IBM Corp., USA).
An unpaired 2-sample t-test was used to detect significant differences in the correlations and lag values between the independent components for controls and patients.
A p-value of 0.05 false discovery rate (FDR) corrected for multiple comparisons was considered significant.
The DTI characteristics were estimated based on previously defined ROIs for each group, and their values were compared using an unpaired 2-sample t-test.
An additional Holm-Bonferroni correction was performed to compensate for the number of ROIs; thus, the p-value was set to 0.01.
To search for correlations between DTI metrics, regional RS-fMRI network changes, and clinical features, the Z-max scores (voxel-wise analysis) of each IC network were extracted for each participant.
A p-value of 0.01 (0.05 / 4) was chosen to compensate for multiple comparisons due to the number of clinical variables.