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

Overview

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.

Interventions

• Device Transcranial Magnetic Stimulation (TMS)
  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 fiel
• Device Electroencephalography (EEG)
  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.
• Device Eye-Tracking
  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

Primary outcome measures

• Topographic Map of Phosphene Localization [Time frame: During the single study visit (session duration is 4 hours).]

Secondary outcome measures (3)

• Correlation between Eye Movements and Phosphene Localization [Time frame: During the single study visit (session duration is 1-4 hours).]
• Change in Brain Activity measured by EEG [Time frame: During the single study visit (session duration is 1-4 hours).]
• Change in Psychomotor Performance [Time frame: Baseline (before TMS session) and after the TMS session (approximately at 4 hours).]

Eligibility criteria

Inclusion criteria

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.

Exclusion criteria

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.

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

Non-randomized

Model

Parallel assignment

Masking

Open label

Primary purpose

Basic science

Study locations

Russia · 1 center

• Skolkovo Institute of Science and Technology (Skoltech) — Moscow

Identifiers

NCT: NCT07110493 · Skoltech-N15

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗