P119 Repetitive TMS can modulate local phase and global phase synchronization of human brain activity

Abstract

The brain is certainly a nonlinear dynamical system which exhibits intriguing features such as oscillations and synchronization of neural activity. A number of studies have indicated that synchronous neuronal oscillations in different frequency bands are responsible for distinct classes of cognitive processes, e.g. perception and cognition. Furthermore, large-scale phase synchronization of oscillatory activity is a plausible mechanism for network communication between distant areas. To gain a further understanding of the causal links between phase synchronous neural oscillations and cognitive functions, we tested if we can directly manipulate the local and global phase dynamics of ongoing oscillations by TMS (Transcranial magnetic stimulation)-EEG (Electroencephalography) concurrent recordings in the human brain. Fourteen healthy volunteers participated in the experiment after giving written informed consent. While participants fixate a central cross with earplugs to attenuate TMS click sound, single-shot TMS, or repetitive TMS (rTMS) (5, 11, 23 Hz, 5-pulse trains) were delivered to the right visual or the left motor cortices at the intensity of 90% active motor threshold. We removed TMS-related EEG artifact by a combination of linear interpolation and ICA. We assessed spatiotemporal profiles regarding instantaneous phase and amplitude dynamics for the EEG data. At the local stimulation site, we observed prominent phase locking at each stimulation frequency in both visual and motor cortices. We found that phase locking was progressively enhanced by successive TMS pulses within a stimulus train. Moreover, the enhanced phase locking was likely to last for a few cycles after stimulation. Intriguingly, phase synchronization between the stimulation area and other brain areas was also enhanced at the stimulation frequency. We have demonstrated that rTMS can control local and global phase synchronization of ongoing oscillations in a frequency-specific way. rTMS, therefore, can be a promising tool for probing causal links between large-scale phase synchronization and brain functions in future We suggest that there is a great potential to aid and augment the disabled human performance associated with impaired synchrony by boosting synchrony in a frequency-specific manner by rTMS.