Repetitive transcranial magnetic stimulation (rTMS) has emerged as an alternative treatment for depression. However, rTMS outcomes show significant intra- and inter-subject variability, limiting its efficacy. This variability is influenced by the individual’s brain state at the time of stimulation, making it crucial to understand how brain states modulate TMS effects. This project investigates how TMS signal propagation is influenced by the cognitive and oscillatory brain state during stimulation, aiming to enhance its scientific reliability and (clinical) effectiveness. Using simultaneous TMS-EEG-fMRI, we will explore how momentary brain oscillations during a cognitive task modulate prefrontal TMS effects in healthy participants. Our goal is to identify task-related oscillatory parameters that elicit the most robust TMS responses. Building on these findings, we will use transcranial alternating current stimulation (tACS) to phase-align TMS delivery with endogenous brain oscillations. Finally, we will apply these insights in a clinical context, testing whether phase-locking TMS pulses to the brain oscillations generated by tACS will improve the efficiency of signal propagation through frontolimbic networks in patients with depression, resulting in improvements in cognitive and affective functioning. This project aims to enhance rTMS interventions by tailoring them to dynamic brain states, overcoming variability, and enabling more reliable and effective rTMS applications.