Resting - State EEG Indicates Unstable Microstates in Visual Snow Syndrome

Background: EEG microstates account for a significant amount of the variance in resting-state EEG activity and are considered the basic building blocks of human neurological processes. We analyzed the characteristics of EEG microstates in patients with visual snow syndrome (VSS) with and without migraine and compared these results with those of a matched control group. VSS is a syndrome characterized by a spectrum of visual symptoms, including photophobia, and enhanced entoptic phenomena. The main symptom of VSS is the perception of flickering dots throughout the visual field, described as looking through a snowy television screen. Cause and pathophysiology of VSS are still unknown.

Method: Resting-state EEG recordings were selected from a cohort of 21 subjects with visual snow syndrome (VSSP, 8 females, 33 ± 9.56 years) and 21 control patients (8 females, 33 ± 11.1 years). Matching was based on diagnosed VSS, age, sex, and migraine status. A comparative analysis of microstate (MS) parameters between these two groups was performed. The calculation involved the four widely accepted canonical microstate classes, namely A (auditory & visual processing, arousal), B (visual processing), C (self-reflection, salience), and D (dorsal attention network).

Results: We found significant differences between groups and between microstates in resting-state EEG in the life span and amplitude of microstates. VSSP showed an overall shorter duration and lower mean global field power (GFP) of microstates compared to controls. In addition, we found an aberrant syntax of microstate class A. Compared to controls, microstate A changed more often to class B and less frequently to microstate class C in VSSP.

Conclusion: By examining resting-state EEG microstate features, we were able to investigate neurobiological mechanisms indicative of altered cortical excitability and aberrant shifts between neural networks in VSSP. Therefore, abnormalities in sensory and cognitive processing are suspected. However, to gain deeper insight into the pathophysiology of VSS, further studies with subjects with homogenous comorbidities are indicated.