Is Visual Snow a Thalamo-Cortical Dysrhythmia of the Visual Processing System - A Magnetoencephalogram Study (PDF)

Visual snow (VS) has been described as a unique clinical entity, which may occur with increased neuronal excitability. (1) Sensory information processing relies on the interactions between thethalamus and cortex. When hyperexcitability affects cortical networks, it can lead to thalamocortical dysrhythmias, resulting in tinnitus. (2) We hypothesize that VS is the visual manifestation ofthalamocortical dysrhythmia. Visual cortex gamma oscillations reflect cognitive processing and alpha oscillations are associatedwith thalamically generated pulses of cortical inhibition, altering information processing. (3) Thisoscillatory network activity is a characteristic property of the thalamocortical system.Therefore, we used Magnetocephalography (MEG) to record the visual cortex oscillatory dynamics,as a measure of possible thalamocortical dysrhythmia in VS patients and controls.

Tuesday, March 10th from 9:00 - 9:15 am Is Visual Snow a thalamo-cortical dysrhythmia of the visual processing system - a magnetoencephalogram study Jenny Hepschke1, Andrew Etchell2, Robert Seymour2, Paul Sowman2, Clare Fraser3 Save Sight Institute, Sydney NSW, Australia, 2Department of Cognitive Science, Macquarie University, Sydney NSW, Australia,3 Sight Institute, Faculty of Health and Medicine, The University of Sydney, Sydney NSW, Australia 1 Introduction: Visual snow (VS) has been described as a unique clinical entity, which may occur with increased neuronal excitability. (1) Sensory information processing relies on the interactions between thethalamus and cortex. When hyperexcitability affects cortical networks, it can lead to thalamocortical dysrhythmias, resulting in tinnitus. (2) We hypothesize that VS is the visual manifestation ofthalamocortical dysrhythmia. Visual cortex gamma oscillations reflect cognitive processing and alpha oscillations are associatedwith thalamically generated pulses of cortical inhibition, altering information processing. (3) Thisoscillatory network activity is a characteristic property of the thalamocortical system.Therefore, we used Magnetocephalography (MEG) to record the visual cortex oscillatory dynamics,as a measure of possible thalamocortical dysrhythmia in VS patients and controls. Methods: 20 patients diagnosed with VS and age-matched controls underwent MEG testing (MEG160 Model PQ1160R-N2,KIT). Results were recorded during resting state and while subjects were visually engaged with a static grating presented for 1.5s. Alterations in MEG signals were assessed between the task types, and participant groups. Neuronal synchronisation in the gamma band (30-100Hz) and oscillatory activity in the alpha band (8-13Hz), were measured in the V1 primary visual cortex. Results: The resting state power spectral density in V1 was similar between VS and controls. During the visual gratings, the increase in gamma power and peak frequency in V1 was similar for the two groups. However, there was a lower alpha peak frequency and greater reduction in alpha power in the controls compared with the VS group at ~11Hz. Alpha-gamma phase-amplitude coupling in V1 is shifted towards lower alpha frequencies for VS patients. Conclusions: The observed changes in visual cortex alpha oscillations provide evidence that neuronal activity is less able to be inhibited through the thalamic pathways in VS patients. This supports the hypothesis that VS is associated with a thalamocortical dysrhythmia. References: 1. Bou Ghannam A, Pelak VS. Visual Snow: a Potential Cortical Hyperexcitability Syndrome. Curr Treat Options Neurol. 2017 Mar;19(3):9. 2. De Ridder D, Vanneste S, Langguth B, Llinas R. Thalamocortical Dysrhythmia: A Theoretical Update in Tinnitus Front Neurol. 2015; 6: 124. 3. Bonnefond, M., S. Kastner, and O. Jensen, Communication between Brain Areas Based on Nested Oscillations. eNeuro, 2017. 4(2). Keywords: Higher visual cortical functions, Higher visual functions Financial Disclosures: The authors had no disclosures. Grant Support: This study was kindly supported by the NANOS Pilot Grant scheme. Contact Information: Dr Jenny Hepschke [e-mail] 2020 Annual Meeting Syllabus | 305