The purpose of this basic science study is to better understand human visual perception. Phosphenes are flashes of light that can be induced using Transcranial Magnetic Stimulation (TMS). The location of these phosphenes is known to change with eye movements, but the exact influence of these movements is not fully understood.
The main questions this study aims to answer are:
How does stimulating specific areas of the visual cortex relate to where a person perceives a phosphene? How do eye movements affect the accuracy of mapping these sensations? The study will enroll three groups of adults (aged 18-65): patients with Visual Snow Syndrome, color-blind participants, and healthy volunteers.
During the experiment, participants will receive single-pulse TMS to their visual cortex. Simultaneously, their eye movements will be monitored with an eye-tracker, and their brain activity will be recorded with EEG. Participants will be asked to report the location of the perceived light flashes. This will help create a map of the brain areas responsible for visual sensations and clarify how eye movements influence this process.
None
None
Parallel
Transcranial Magnetic Stimulation (TMS)
DeviceSingle-pulse TMS is applied to specific areas of the visual cortex to non-invasively induce the perception of phosphenes (brief flashes of light). Stimulation is delivered using a TMS device, with the operator controlling the intensity and frequency parameters to a level equal to the phosphene-evoking threshold. During stimulation, participants are seated comfortably and asked to report the location of perceived phosphenes on a monitor and a physical grid, helping to map the cortical visual field.
Electroencephalography (EEG)
DeviceContinuous brain electrical activity is recorded using a 128-channel gel-based EEG system (Skoltech). The EEG cap is fitted to the participant's head to capture neural responses with high temporal resolution throughout the session. The collected data is used to analyze brain activity changes, including the P300 component and other event-related potentials, to identify neural correlates of phosphene perception and the effects of TMS.
Eye-Tracking
DeviceEye movements are continuously monitored using a Tobii Defusion 2 eye-tracker (Skoltech) operating at 60 Hz. This device provides high-accuracy measurements of gaze fixation and saccades. Participants are instructed to fixate their gaze on one of five predetermined points on a screen (center, top, bottom, left, right), with the fixation point being determined randomly for each trial. The eye-tracking data is analyzed to assess the influence of gaze position on phosphene localization and to study any stimulation-induced changes in eye movement patterns.
Topographic Map of Phosphene Localization
Creation of a map showing the correlation between specific stimulated areas of the visual cortex and the reported location of perceived phosphenes in the visual field. The map is generated based on participant reports during TMS stimulation.
Correlation between Eye Movements and Phosphene Localization
Analysis of eye-tracking data to quantify the influence of gaze fixation points and saccadic eye movements on the reported location of TMS-induced phosphenes.
Change in Brain Activity measured by EEG
Analysis of EEG data, including tensor analysis and the P300 event-related potential, to identify changes in brain activity and correlations with phosphene perception and localization.
Change in Psychomotor Performance
Assessment of visual-motor coordination and attention levels measured by a psychomotor test. The test requires participants to track a moving target on a screen. Performance is measured by the number of errors (deviations from the target).
Click on the lead sponsor to view all of their trials.
Skolkovo Institute of Science and Technology
Lead sponsor
I.M. Sechenov First Moscow State Medical University
Collaborator
