Insular and occipital changes in visual snow syndrome: a BOLD fMRI and MRS study

Abstract

Objective To investigate the pathophysiology of visual snow (VS), through a combined functional neuroimaging and magnetic resonance spectroscopy (1H‐MRS) approach. Methods We applied a functional MRI block‐design protocol studying the responses to a visual stimulation mimicking VS, in combination with 1H‐MRS over the right lingual gyrus, in 24 patients with VS compared to an equal number of age‐ and gender‐matched healthy controls. Results We found reduced BOLD responses to the visual stimulus with respect to baseline in VS patients compared to controls, in the left (k = 291; P = 0.025; peak MNI coordinate [‐34 12 ‐6]) and right (k = 100; P = 0.003; peak MNI coordinate [44 14 ‐2]) anterior insula. Our spectroscopy analysis revealed a significant increase in lactate concentrations in patients with respect to controls (0.66 ± 0.9 mmol/L vs. 0.07 ± 0.2 mmol/L; P < 0.001) in the right lingual gyrus. In this area, there was a significant negative correlation between lactate concentrations and BOLD responses to visual stimulation (P = 0.004; r = −0.42), which was dependent on belonging to the patient group. Interpretation As shown by our BOLD analysis, VS is characterized by a difference in bilateral insular responses to a visual stimulus mimicking VS itself, which could be due to disruptions within the salience network. Our results also suggest that patients with VS have a localized disturbance in extrastriate anaerobic metabolism, which may in turn cause a decreased metabolic reserve for the regular processing of visual stimuli.

Occipital cortex and cerebellum gray matter changes in visual snow syndrome

“…Several pathophysiologic hypotheses for the genesis of VSS have been proposed in the literature, 27 and hyperexcitation of primary and secondary visual cortices 28 – 31 seems to be one of the most plausible. In a condition where internal visual information is constantly being perceived, a state of increased cortical activation, justified by a form of processing overload, is plausible.…”

Abnormal Connectivity and Brain Structure in Patients With Visual Snow

“…A recent study reported alterations in neurotransmission and fMRI signal strength during visual stimulation mimicking VS (Puledda et al, 2020). The authors observed reduced bilateral anterior insula BOLD responses to the visual stimulus with respect to baseline in VS patients compared to controls.…”

“…Increases in gray matter volume were seen in the right (R) lingual gyrus [p = 0.014, family-wise error (FWE) corrected, t-value = 4.61] in the patient group when compared to controls. noted in the FEF in patients with VS (Puledda et al, 2020). The FEF (but also the supramarginal gyrus) is involved not only in the control of eye movements but also in the control of visual awareness and visuospatial attention (Vernet et al, 2014;Quentin et al, 2015), and hyperconnectivity of this region to the AG might indicate abnormal attentional control.…”

“…In a few studies, occipital bending has been mentioned to co-occur in some patients with VS (Unal-Cevik and Yildiz, 2015;Yildiz et al, 2019) and may be related to depression (Maller et al, 2014(Maller et al, , 2015. Recently, Puledda et al (2020) reported metabolic and functional alterations using MR spectroscopy and taskbased fMRI, respectively. The authors concluded that patients with VS demonstrated disturbed processing in the salience network, as the bilateral insular cortex showed lower BOLD signal responses in patients than those in controls.…”

“…The authors concluded that patients with VS demonstrated disturbed processing in the salience network, as the bilateral insular cortex showed lower BOLD signal responses in patients than those in controls. On the other hand, the elevated lactate concentration of the (right) lingual gyrus was interpreted as a sign of hyperexcitability in VS patients (Puledda et al, 2020).…”