Brain Cortical Stimulation Thresholds to Different Magnetic Field Sources Exposures at Intermediate Frequencies

Permissible field strengths in the international guidelines/standard for human protection are derived from peripheral nerve system stimulation at the intermediate frequencies where electrostimulation (attributable to axon activation) is more dominant than thermal effect. Recently, multiscale computation has been used to investigate neuron stimulation thresholds by incorporating individual neurons into realistic head models. However, the consistency of excitation models and permissible levels to specific target tissues (central nervous system) needs to be clarified. This article aims to investigate brain cortical stimulation thresholds using a multiscale computational approach for different scenarios of magnetic field exposures. The magnetic exposures include transcranial magnetic stimulation, uniform exposure, and wireless power transfer systems. Our results confirmed the consistency of the multiscale computations of the cortical thresholds between two independent groups for electromagnetic exposure of transcranial magnetic stimulation (thresholds in the range of motor cortex activation). We also quantified the conservativeness of permissible field strengths of international guidelines/standards at intermediate frequencies. Finally, with the multiscale approach, we confirmed that 10 000 kW of transmitting power of wireless power transfer (WPT) in an electric vehicle charging system may not induce an adverse effect for cortical activation.