EEG-based brain fingerprints elicited by focal transcranial magnetic stimulation of the primary motor cortex

Idiosyncratic patterns of brain activity, often referred to as functional "brain fingerprints", capture the unique organization of an individual's brain dynamics and may serve as markers of brain dysfunction. Here, we tested the hypothesis that external perturbation may steer brain activities into individualized trajectories that facilitate identification. Twelve healthy participants received single-pulse transcranial magnetic stimulation (TMS) to the left primary motor cortex (M1) at 120% of their resting motor threshold (RMT), while 64-channel EEG recorded cortical responses to TMS. Single TMS pulse transiently increased idiosyncrasy in both, local and network-level brain dynamics, relative to baseline. Within-subject stability increased in time-frequency power envelopes, inter-trial phase clustering, and imaginary part of coherency, the latter reflecting functional connectivity. These effects were strongest in the beta frequency band and in regions surrounding the stimulation site. Together, these results show that single-pulse TMS reliably amplifies individual brain fingerprints, offering a stimulation-based method for probing subject-specific brain dynamics and potentially strengthen the sensitivity and robustness of fingerprinting metrics in clinical and personalized neuromodulation contexts.