Decoding asymmetric neural dynamics in visual processing via TMS-induced cortical effective connectivity

Exploring brain connectivity is made possible through the combination of transcranial magnetic stimulation and electroencephalography (TMS–EEG) signals. While previous research has investigated hemispheric asymmetries in signal propagation at the electrode space following occipital TMS, this work extends this exploration at the source level. The sources of the neural activity were reconstructed using EEG data and mapped into regions of interest. The TMS evoked potential (TEP) was estimated using a Bayesian approach, which provides better results when the number of trials is limited. Subsequently, time-varying effective connectivity was calculated for uncovering hemispheric asymmetries in the dynamics of signal propagation. A distinct contralateral influence emerged following stimulation of the left occipital lobe, especially toward the parietal and frontal lobes, aligning with the observations on the scalp. In conclusion, our study advances the understanding of brain connectivity dynamics, particularly in hemispheric interactions, and paves the way for further insights into the implications of TMS on neural networks.