Brain-state dependent non-invasive brain-stimulation with real-time closed-loop simultaneous EEG/TMS

Abstract

Objective We present initial results using a real-time closed-loop simultaneous EEG/TMS set-up to investigate the impact of the instantaneous state of oscillatory brain activity at the time of a TMS pulse. Methods EEG data is recorded and analyzed in real-time using a signal processing PC system. A TMS pulse is triggered when the recorded EEG signal matches predetermined parameters (spectral power and phase at a given frequency). Results Brain-state dependent stimulation is achieved based on ongoing alpha-band oscillatory EEG activity with an overall latency in the closed-loop set-up below 2.5 ms. The impact of instantaneous brain-state on the variability of TMS-evoked muscle-evoked potentials and EEG responses as well as on the direction and magnitude of TMS-induced plasticity is quantified. Conclusions The instantaneous state of oscillatory brain activity at the time of a TMS pulse is a relevant factor influencing both the responsiveness of the brain to stimulation as well as the induction of plasticity. Key message The brain we stimulate with one pulse is not the same brain that we stimulate with the next pulse. The role of spontaneous oscillatory activity can be investigated with novel stimulation protocols that are time-locked to the instantaneous parameters of the simultaneously recorded EEG signal.