Probing dynamical cortical gating of attention with concurrent TMS-EEG

Background Attention facilitates gating of information from the sending brain area to receiving areas, with this being achieved by dynamical change in effective connectivity between cortices. However, it is difficult to assess effective connectivity, which refers to the causal influence of one cortical area on another. Objective The aim of this study is to directly probe the effective connectivity between cortical areas, which is modulated by covertly shifted attention, excluding the thalamic influence. Methods Transcranial magnetic stimulation (TMS) was used to directly perturb the right retinotopic visual cortex in task-relevant (TR) and task-irrelevant (TIR) networks, and the impact of this was tracked to other areas by concurrent use of electroencephalography (EEG). Results Key finding was that TMS to the TR hemisphere led to a stronger evoked potential than did stimulation to the TIR hemisphere. Moreover, stronger beta- and gamma-band effective connectivities assessed as lagged phase synchronizations between stimulated areas and other areas were observed when TMS was delivered to the TR area. These effects were more enhanced when they preceded more prominent alpha lateralization, which is known to be associated with gating information. Conclusion Our results indicate that attention-regulated cortical excitability and feedforward dynamical effective connectivity can be probed by direct cortical stimulation to the TR or TIR area, thereby bypassing thalamic gating. These results bear out the idea that TMS-EEG could help to characterize changes in the functional architecture of brain networks that are required for rapid adaptation to the environment or due to brain diseases. Highlights Attention-regulated cortical excitability and effective connectivity were probed by TMS-EEG. Stronger TMS evoked potentials were observed in the task-relevant visual hemisphere. Strong effective connectivity between task-relevant visual cortex and other areas were found.