Evaluating Human Perception Thresholds in Magnetic Stimulation Using Experimental Measurements and Modelling

Area of Science:

• Neuroscience
• Biophysics
• Medical Imaging

Background:

• Transcranial magnetic stimulation (TMS) relies on induced electric fields to modulate neural activity.
• Accurate prediction of perception thresholds is crucial for optimizing TMS efficacy and safety.
• Current models often simplify anatomical complexities, potentially limiting predictive accuracy.

Purpose of the Study:

• To investigate if induced electric fields alone can predict human perception thresholds in magnetic stimulation.
• To develop and validate subject-specific, anatomically realistic models for predicting stimulation effects.
• To compare findings with simplified modelling approaches and inform safety guideline refinement.

Main Methods:

• Collected perception thresholds from 24 participants using a figure-of-eight coil and method of adjustment.
• Constructed subject-fitted, anatomically realistic forearm models from MRI data.
• Computed induced electric fields using the finite element method with probabilistic conductivities.
• Applied spatial averaging and percentile analysis to electric field data.

Main Results:

• The perception threshold was determined to be 32.2 V/m for a specific magnetic pulse.
• The induced electric field explained 48% of the variance in perception thresholds (adjusted R² = 0.48).
• Simplified cylindrical models require a scaling factor of 1.4 to match realistic model predictions.

Conclusions:

• Induced electric fields alone do not fully account for human perception thresholds in magnetic stimulation.
• Anatomically realistic modelling provides more accurate predictions than simplified approaches.
• Findings contribute to refining safety guidelines for magnetic stimulation therapies.