Altered functional connectivity strength between structurally and functionally affected brain regions in visual snow syndrome

Abstract

Visual snow syndrome (VSS) is a neurological disorder that is predominantly characterized by persistent, dynamic visual disturbances, experienced across the entire visual field. Earlier research highlighted the significance of distinct brain regions, exhibiting alterations in both anatomical structure and functional characteristics. To further investigate the functional role of these regions, we examined the resting-state connectivity between these areas in individuals with VSS and the relation with VSS symptoms and oculomotor measures of visual processing. Forty patients with VSS (53% females; age = 33.2 ± 10.1 years; 22 with migraine) and 60 healthy controls (58% females; age = 32.0 ± 9.2 years) were scanned using 7 Tesla MRI system. High spatial and temporal resting-state (RS) functional (TR = 800 ms, 1.6 mm isotropic) and anatomical (MP2RAGE, 0.75 mm isotropic) images were acquired. Resting-state data were pre-processed (motion correction, temporal filtering and spatial smoothing), functional connectivity was calculated between regions of interest and compared between groups. Significant metrics were compared with VSS patients with and without migraine and correlated with oculomotor measures (prosaccade and anti-saccade latencies), number of VSS symptoms, self-rated VSS intensity and perceived disruptiveness. Compared to healthy controls, VSS patients demonstrated significantly higher connectivity between the supramarginal gyrus and lateral occipital cortex (P = 0.016) and fusiform (P = 0.007), lower connectivity between the supramarginal gyrus and pallidum (P = 0.032), as well as between the parahippocampal gyrus and lateral occipital cortex (P = 0.007), which related to higher perceived disruptiveness (P = 0.002, r = -0.489). No differences were found between VSS with and without migraine. This study revealed altered functional connectivity strength in individuals with VSS, suggesting stronger connectivity between cortical areas, particularly centred around the supramarginal gyrus, and disconnections with deep grey matter and temporal cortices, which associated with perceived disruptiveness of VSS.

Keywords: 7T; fMRI; functional connectivity; resting-state MRI; visual snow syndrome.

Graphical Abstract

Figure 1

Functional resting-state processing pipeline. (A) Cortical and subcortical segmentation using the T1-weigthed MP2RAGE image and FreeSurfer. (B) Areas that differentiate visual snow syndrome (VSS) patients from healthy individuals (HC), both structurally and functionally, were selected to study further. Structural areas of significant differences are coloured with effect size and functional areas of significant differences with P values (−Log10). Images reproduced from Strik et al. 2022 and Strik et al. 2023. (C) Pre-processed functional MRI signals were extracted from regions of interest and connectivity strength between node pairs was computed using correlation coefficients (r), resulting in an 8 × 8 connectivity matrix for each participant (VSS n = 40, HC n = 60).

Figure 2

Altered functional connectivity in visual snow syndrome. The connectivity differences between visual snow syndrome (VSS, n = 40) and healthy controls (HCs, n = 60) were assessed using independent t-tests and significant differences are visualized in A by large circles and lines between those regions and in B by a star in the connectivity matrix. Compared to HC, VSS patients showed higher connectivity between the supramarginal gyrus (SMG) and lateral occipital cortex (LOC, P = 0.016, t = −2.4641) and fusiform (FUS, P = 0.007, t = −3.5020) and lower connectivity between SMG and pallidum (PAL, P = 0.032, t = 2.1795), as well as between the parahippocampal gyrus (PHC) and LOC (P = 0.007, t = 2.7640). (C) In VSS, lower connectivity between the LOC and PHC related to higher perceived disruptiveness (P = 0.002, r = −0.489, Spearman correlation). BSTS, banks of superior temporal sulcus; PUT, putamen; SPC, superior parietal cortex.