Study of Visual Perception Phenomena: Phosphene Mapping Induced by TMS and Its Relationship With Eye Movements

NCT07110493 | Recruiting

• 1 other identifier: Skoltech-N15
• Study Type: interventional
• Target: 50
• Locations: 1 country
• Sites: 1

Brief Summary

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.

Conditions

Visual Snow Syndrome; Color Blindness; Healthy Volunteer

Outcome Measures

Primary Outcomes (1)

• 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.

  During the single study visit (session duration is 4 hours).

Secondary Outcomes (3)

• Correlation between Eye Movements and Phosphene Localization

  During the single study visit (session duration is 1-4 hours).

• Change in Brain Activity measured by EEG

  During the single study visit (session duration is 1-4 hours).

• Change in Psychomotor Performance

  Baseline (before TMS session) and after the TMS session (approximately at 4 hours).

Study Arms (3)

Patients with Visual Snow Syndrome

EXPERIMENTAL

Participants diagnosed with Visual Snow Syndrome according to ICHD-3 criteria. This group will undergo TMS, EEG, and eye-tracking to study the mechanisms of visual perception.

Device: Transcranial Magnetic Stimulation (TMS); Device: Electroencephalography (EEG); Device: Eye-Tracking

Color-blind Participants

EXPERIMENTAL

Participants with a confirmed diagnosis of color blindness. This group will undergo TMS, EEG, and eye-tracking to compare visual processing with other groups.

Device: Transcranial Magnetic Stimulation (TMS); Device: Electroencephalography (EEG); Device: Eye-Tracking

Healthy controls

ACTIVE COMPARATOR

Healthy volunteers with no history of neurological, psychiatric, or visual disorders. This group serves as a baseline to compare the findings from the experimental arms.

Device: Transcranial Magnetic Stimulation (TMS); Device: Electroencephalography (EEG); Device: Eye-Tracking

Interventions

Transcranial Magnetic Stimulation (TMS) DEVICE

Single-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.

Color-blind Participants; Healthy controls; Patients with Visual Snow Syndrome

Electroencephalography (EEG) DEVICE

Continuous 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.

Color-blind Participants; Healthy controls; Patients with Visual Snow Syndrome

Eye-Tracking DEVICE

Eye 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.

Color-blind Participants; Healthy controls; Patients with Visual Snow Syndrome

Eligibility Criteria

• Age: 18 Years - 65 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• For the "Patients with Visual Snow Syndrome" Arm:
• Confirmed diagnosis of Visual Snow Syndrome according to the International Classification of Headache Disorders, 3rd edition (ICHD-3) criteria.
• Presence of persistent, dynamic, tiny dots ("visual snow") across the entire visual field.
• Presence of at least one of the following additional visual symptoms:
• Palinopsia (prolonged afterimages). Photophobia (hypersensitivity to light). Nyctalopia (impaired night vision). Blurred vision. Patients whose symptoms appeared after a SARS-CoV-2 viral illness may be included.
• For the "Color-blind Participants" Arm:
• Presence of a color perception disorder. Must have a formal diagnosis of color blindness confirmed by specific ophthalmologic tests (e.g., Ishihara, Rabkin, Justova, or Stilling polychromatic plates, or the Farnsworth-Munsell test).
• For the "Healthy Controls" Arm:
• Absence of any active or past neurological, psychiatric, or ophthalmological disorders.

You may not qualify if:

• General Criteria (Applicable to all participants):
• Use of psychotropic drugs. Any contraindications to Transcranial Magnetic Stimulation (TMS), such as a history of epilepsy, seizures, or metallic implants in the head.
• Pregnancy.
• Specific to the "Patients with Visual Snow Syndrome" Arm:
• Presence of any organic abnormalities in the eyes or visual system identified during a standard ophthalmologic examination.
• Presence of comorbid psychiatric disorders or other medical conditions (e.g., migraine with aura) that could explain the symptoms.
• Specific to the "Color-blind Participants" Arm:
• Any non-congenital cases of color blindness. Presence of concomitant visual impairments that could affect visual perception independently of color blindness, such as cataracts, glaucoma, or macular degeneration.
• Presence of concomitant neurological or psychiatric diseases, such as schizophrenia, epilepsy, or mood disorders, that could affect the study results.

Sponsors & Collaborators

• Skolkovo Institute of Science and Technology: lead
• I.M. Sechenov First Moscow State Medical University: collaborator

Study Sites (1)

Skolkovo Institute of Science and Technology (Skoltech)

Moscow, Russia

RECRUITING

MeSH Terms

Conditions

visual snow syndrome; Color Vision Defects

Interventions

Transcranial Magnetic Stimulation; Electroencephalography; Eye-Tracking Technology

Condition Hierarchy (Ancestors)

Vision Disorders; Sensation Disorders; Neurologic Manifestations; Nervous System Diseases; Cone Dystrophy; Eye Diseases, Hereditary; Eye Diseases; Signs and Symptoms; Pathological Conditions, Signs and Symptoms

Intervention Hierarchy (Ancestors)

Magnetic Field Therapy; Therapeutics; Diagnostic Techniques, Neurological; Diagnostic Techniques and Procedures; Diagnosis; Electrodiagnosis; Eye Movement Measurements; Diagnostic Techniques, Ophthalmological

Central Study Contacts

Akinshin R.

CONTACT

79999810206; Roman.Akinshin@skoltech.ru

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: NON RANDOMIZED
• Masking: NONE
• Purpose: BASIC SCIENCE
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Study Record Dates

• First Submitted: July 31, 2025
• First Posted: August 7, 2025
• Study Start: September 10, 2025
• Primary Completion (Estimated): December 10, 2026
• Study Completion (Estimated): December 10, 2026
• Last Updated: August 7, 2025

Record last verified: 2025-07

Locations

RU (1)