Aperiodic Brain Activity Modulates Corticospinal Excitability.

Brain state-dependent transcranial magnetic stimulation (TMS) synchronizes with instantaneous power and is a novel time-precise neuroregulation approach. The key to this approach is using instantaneous power to reliably estimate specific cortical excitability. However, the specific influence of instantaneous power, particularly aperiodic brain activity, on corticospinal excitability is not fully understood. In our study, single-pulse TMS stimulated the primary motor cortex at 110% resting motor threshold (RMT) and 120% RMT, and the electroencephalography and motor-evoked potentials (MEP) were recorded simultaneously. We conducted a five-part analysis, including total power, periodic power, aperiodic power, the aperiodic exponent, and offset, to evaluate the power dependence of corticospinal excitability. We found that the higher the alpha and beta power were, the greater the MEP amplitudes were. The aperiodic component plays a more critical role than the periodic component. Furthermore, corticospinal output was less affected by power at 120% RMT than at 110% RMT. Our findings highlight that the aperiodic component is associated with cortical excitability and may be a valuable parameter for optimizing brain-state-dependent TMS approaches.