Measurement and modeling of peripheral nerve magnetostimulation in a head solenoid from 200 Hz to 88.1 kHz

Motivation: Two previous peripheral nerve magnetostimulation experiments reported increasing thresholds above 25 kHz, which deviates from the hyperbolic strength-duration curve describing thresholds versus frequency. However, high-frequency PNS measurements are sparse and established neurodynamic models have not been validated above 1 kHz. Goal(s): Characterize PNS thresholds in a solenoidal head coil between 200 Hz and 88.1 kHz. Approach: We measure PNS thresholds in four healthy volunteers and compare to predictions of our electromagnetic-neurodynamic PNS model. Results: The measured thresholds increase 36% on average from 16.9 kHz to 66.7 kHz, which is at odds both with the hyperbolic scaling as well as our detailed PNS modeling. Impact: Our strength-duration measurements show that the greatest stimulation propensity is ~17 kHz and PNS thresholds remain relatively low at frequencies greater than 20 kHz, which is important for informing the design of MRI and MPI coils.