Quantifying phosphene size using MRI-guided transcranial magnetic stimulation to primary visual cortex
Bibliographic record
Abstract
Visual phosphenes are perceived flashes of light in the absence of retinal input and can be evoked by transcranial magnetic stimulation (TMS) to primary visual cortex (V1). Previous dose-response studies using direct electrical stimulation (DES) of the visual cortex have shown that higher intensities produce larger phosphenes, suggesting increased stimulation intensity affects a larger cortical area. Unlike DES, in TMS intervening tissues such as scalp, skull, and cerebrospinal fluid can attenuate induced electric fields. Prior studies have examined stimulation intensity, but few have investigated how individual differences in phosphene size relate to biophysical factors. The current study examines TMS-induced phosphene size and its relation to phosphene thresholds, scalp-to-cortex distance, and modelled electric field strength measured using MRI-guided stereotaxic neuronavigation and our computer-based phosphene reporting tool. V1 stimulation evoked phosphenes in quadrants of the visual field corresponding to retinotopic region. Perceived phosphene size was negatively correlated with phosphene thresholds, indicating that higher phosphene thresholds led to smaller perceived phosphenes. Age and scalp-to-cortex distance were not correlated with phosphene size, consistent with the notion that scalp-to-cortex distance does not account for different intervening tissue types and corresponding properties. Phosphene size, however, was negatively correlated with electric field strength, indicating that intervening tissue properties may attenuate TMS intensity. These findings suggest that variability in phosphene perception may reflect biophysical factors, such as intervening tissue properties and highlight the importance of accounting for biophysical factors and electric field modelling to better understand variability in TMS-evoked phosphene perception. In addition, using a standardised method such as a phosphene mapping tool to quantify individual differences in TMS response is valuable to facilitate standardization of methods for non-invasive brain stimulation to advance TMS research and optimize its application in clinical settings.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".