Fractional Amplitude of Low-Frequency Fluctuations and Regional Homogeneity Analyses Revealed Altered Local...

Previous studies have revealed alterations of the functional connectivity of the brain networks in ankylosing spondylitis (AS). Fractional amplitude of low-frequency fluctuations (fALFF) and regional homogeneity (ReHo) are both voxel-based functional metrics capable of estimating local spontaneous neural activities. This study aimed to investigate the local spontaneous neural activities in AS patients by utilizing the analytical approaches of fALFF and ReHo.

A total of 78 AS patients and 59 healthy controls (HCs) underwent resting-state functional magnetic resonance imaging. fALFF and ReHo maps were generated to identify brain regions with aberrations of spontaneous neural activities in AS patients. Different frequency bands, including the standard frequency band (0.01-0.1 Hz), slow-5 (0.01-0.027 Hz), and slow-4 (0.027-0.073 Hz), were adopted in the fALFF analysis.

Compared with HCs, AS patients exhibited extensive alterations of fALFF and ReHo values in brain regions belonging to the default mode network (DMN), salience network (SN), frontoparietal network (FPN), sensorimotor network, visual network and the cerebellum. Clusters found in the slow-5 band only showed significantly decreased fALFF values, whereas the slow-4 was the major contributor to the elevated fALFF values in the standard band.

The fALFF and ReHo analyses consistently revealed significantly altered local spontaneous neural activities in AS patients, especially in the DMN, SN and FPN, comprising the triple network model. The slow-4 band might be more sensitive to the elevated fALFF values in AS patients than the slow-5 band. Our findings provide further evidence that the aberrations of the triple network model serve as an important feature of AS from the perspective of local neural activities.