We report a novel subthreshold non-invasive brain stimulation approach that we refer to as kilohertz transcranial magnetic perturbation, or kTMP. kTMP is a magnetic induction method that delivers kHz-frequency cortical E-fields and, through amplitude modulation of the kHz carrier frequency, may mimic E-fields at physiological frequencies. To evaluate the efficacy of kTMP, we used suprathreshold TMS to elicit motor-evoked potentials (MEP) in a peripheral muscle, comparing the amplitude of the MEPs before and after kTMP stimulation. In Experiment 1, we used non-modulated kTMP with an E-field amplitude of 2 V/m over motor cortex. Ten minutes of kTMP stimulation resulted in an increase in cortical excitability in a frequency-specific manner. We replicated this effect in Experiment 2 and found that amplitude-modulation at 20 Hz produced an additional boost in cortical excitability. The only percept associated with kTMP is a faint auditory tone, making kTMP ideal for double-blind experimentation.
kTMP: A New Non-invasive Magnetic Induction Method to Modulate Cortical Excitability