External induction and stabilization of brain oscillations in the human

Background Neural oscillations in the cerebral cortex are associated with a range of cognitive processes and neuropsychiatric disorders. However, non-invasively modulating oscillatory activity remains technically challenging, due to limited strength, duration, or non-synchronization of stimulation waveforms with endogenous rhythms. Objective We hypothesized that applying controllable phase-synchronized repetitive transcranial magnetic stimulation pulses (rTMS) with alternating currents (tACS) may induce and stabilize neuro-oscillatory resting-state activity at targeted frequencies. Methods Using a novel circuit to precisely synchronize rTMS pulses with phase of tACS, we empirically tested whether combined, 10-Hz prefrontal bilateral stimulation could induce and stabilize 10-Hz oscillations in the bilateral prefrontal cortex (PFC). 25 healthy participants took part in a repeated-measures design. Whole-brain resting-state EEG in eyes-open (EO) and eyes-closed (EC) was recorded before (baseline), immediately (1-min), and 15- and 30-min after stimulation. Bilateral, phase-synchronized rTMS aligned to the positive tACS peak was compared with rTMS at tACS trough, with bilateral tACS or rTMS on its own, and to sham. Results 10-Hz resting-state PFC power increased significantly with peak-synchronized rTMS + tACS (EO: 44.64%, EC: 46.30%, p
Highlights • Non-invasively inducing and stabilizing neural oscillations remains challenging. • We develop a controllable phase-synchronized circuit to combine rTMS and tACS. • This circuit was tested for inducing 10 Hz oscillations in healthy prefrontal cortex. • 10 Hz rTMS synchronized to the positive 10 Hz tACS peak induced stable after-effects. • Phase-synchronized stimulation is a viable approach for oscillatory neuromodulation.