Exploring the synchronization of cortical networks via entrainment to intrinsic frequencies

Introduction: Transcranial electrical stimulation (tES), including transcranial alternating current stimulation (tACS) and transcranial direct current stimulation (tDCS), is widely studied for its potential to modulate brain oscillations and connectivity, offering treatment options for neurological disorders like Alzheimer's, Parkinson's, and insomnia. In this study, we focus on investigating the efficacy of tACS and tDCS in entraining intrinsic cortical network oscillations through a computational model.

Materials and methods: We developed a 2D computational cortical neuron model with 2000 neurons (1600 pyramidal and 400 inhibitory), based on the Izhikevich neuron model. The network was structured to generate low-frequency oscillations, particularly within the delta (4 Hz) range. Both tACS and tDCS were simulated to assess their effect on network synchronization. An algorithm was employed to extract the network's intrinsic frequency and align stimulation frequencies accordingly.

Results: Our model successfully generated 4 Hz oscillations, characteristic of delta waves, associated with sleep states. t-ACS stimulation enhanced the power of the 4 Hz frequency, achieving effective synchronization with the intrinsic network dynamics. In contrast, tDCS failed to increase the power of 4 Hz oscillations and disrupted the excitatory-inhibitory balance of the network, reducing connectivity and synchronization. Our results demonstrate that tACS effectively enhances network synchronization and maintains excitatory-inhibitory balance by aligning with the network's intrinsic oscillatory frequency. In contrast, tDCS disrupts these dynamics, reducing connectivity and failing to entrain the target frequency. These findings suggest that tACS may hold greater potential for applications requiring precise network synchronization, while tDCS may have distinct but more limited efficacy in influencing oscillatory activity.

Conclusion: The study demonstrates the superior efficacy of tACS over tDCS in enhancing the synchronization of cortical networks by entraining intrinsic frequencies. Future research may extend this model by incorporating long-term plasticity mechanisms to better understand tES effects over longer time scales.