Transcranial photobiomodulation changes topology, synchronizability, and complexity of resting state brain networks.

Objective Transcranial photobiomodulation (tPBM) is a recently proposed non-invasive brain stimulation approach with various effects on the nervous system from the cells to the whole brain networks. Specially in the neural network level, tPBM may alter the topology and synchronizability of functional brain networks. However, the functional properties of the neural networks after tPBM are still poorly clarified. Approach Here, we employed electroencephalography (EEG) and different methods (conventional and spectral) in the graph theory analysis to track the significant effects of tPBM on the resting state brain networks. The non-parametric statistical analysis showed that just one short-term tPBM session over right medial frontal pole can significantly change both topological (i.e., clustering coefficient, global efficiency, local efficiency, eigenvector centrality) and dynamical (i.e., energy, largest eigenvalue, and entropy) features of resting state brain networks. Main results The topological results revealed that tPBM can reduce local processing, centrality, and laterality. Furthermore, the increased centrality of central electrode (Cz) was observed. Significance These results suggested that tPBM may alter topology of resting state brain network to facilitate the neural information processing. However, the reduction of local processing after tPBM can be assumed as a negative point for this approach. On the other hand, the dynamical results showed that tPBM reduced stability of synchronizability but increased complexity in the resting state brain networks. These effects can be considered in association with the increased complexity of connectivity patterns among brain regions and the enhanced information propagation in the resting state brain networks. Overall, both topological and dynamical features of brain networks suggest that although tPBM decreases local processing and disrupts synchronizability of network, but it can increase the level of information transferring and processing in the brain network.