Uncovering the neurological substrates underlying restlessness in cluster headache - A functional MRI study

Restlessness or agitation is one of the core symptoms of cluster headache (CH). However, the neurological substrate underlying this phenomenon has not been thoroughly analyzed. Whether they are attributed to the core aggression circuit or other CH-related structures remains unclear. The aim of this study is to use functional neuroimaging to elucidate the underlying mechanism of restlessness or agitation in CH.

We prospectively recruited consecutive patients with CH from the Headache Clinic of Taipei Veterans General Hospital between Jan 2022 and July 2025. Patients who consistently reported either the presence or absence of restlessness during CH attacks were enrolled and categorized into two groups: restlessness and non-restlessness. All enrolled patients underwent a functional magnetic resonance imaging (fMRI) scan. In the restlessness group, patients were required to exhibit restlessness during the fMRI scan, whereas those in the non-restlessness group showed no restlessness at the time of scanning. In this study, 32 regions of interest (ROIs) relevant to CH pathophysiology and the core aggression circuit were selected. To identify restlessness-related networks, ROI-to-ROI functional connectivity was compared between the restlessness and non-restlessness groups. To investigate downstream network for restlessness, ROI-to-voxel analyses were conducted using a general linear model, with ROIs showing significant differences in the initial ROI-to-ROI analysis as seeds. Multiple comparisons were corrected using both the false discovery rate (FDR) and family-wise error (FWE) methods.

A total of 24 patients with CH were recruited and categorized into two groups: restlessness (N = 14) and non-restlessness (N = 10). The ROI-to-ROI functional connectivity analysis of CH patients with restlessness revealed a significant connection between the non-pain side locus coeruleus (LC) and the pain-side substantia nigra pars compacta (SNpc), which survived FDR correction (p-FDR = 0.016). Seed-based general linear model analysis further revealed decreased connectivity between the pain-side SNpc and pain-side superior frontal gyrus, which survived FWE correction (p = 0.037). However, there were no significant cortical connectivity from the LC survived the FDR correction.

Our fMRI findings suggest that the neurological substrates of restlessness in CH involve the LC and SNpc rather than the core aggression network. Weakened connectivity from the SNpc to the superior frontal cortex may represent the downstream pathway contributing to restlessness in CH.