Data for: Kilohertz Transcranial Magnetic Perturbation (kTMP): A new non-invasive method to modulate cortical excitability

Non-invasive brain stimulation (NIBS) provides a method for safely
perturbing brain activity and has been employed in basic research to test
hypotheses concerning brain-behavior relationships with increasing
translational applications. We introduce and evaluate a novel subthreshold
NIBS method: kilohertz transcranial magnetic perturbation (kTMP). kTMP is
a magnetic induction method that delivers continuous kHz-frequency
cortical electric fields (E-fields) which may be amplitude-modulated to
potentially mimic electrical activity at endogenous frequencies. We used
TMS to compare the amplitude of motor-evoked potentials (MEPs) in a hand
muscle before and after kTMP. In Experiment 1, we applied kTMP for 10 min
over the motor cortex to induce an E-field amplitude of approximately 2.0
V/m, comparing the effects of waveforms at frequencies of 2.0, 3.5, or 5.0
kHz. In Experiments 2 and 3, we used two forms of amplitude-modulated kTMP
with a carrier frequency at 3.5 kHz and modulation frequencies of either
20 or 140 Hz. The only percept associated with kTMP was an auditory tone,
making kTMP amenable to double-blind experimentation. Relative to sham
stimulation, non-modulated kTMP at 2.0 and 3.5 kHz resulted in an increase
in cortical excitability, with Experiments 2 and 3 providing a replication
of this effect for the 3.5 kHz condition. Although amplitude-modulated
kTMP increased MEP amplitude compared to sham, no enhancement was found
compared to non-modulated kTMP. kTMP opens a new experimental NIBS space,
inducing relatively large amplitude subthreshold E-fields able to increase
cortical excitability with minimal sensation.