What can neurofeedback and transcranial alternating current stimulation tell us about cross-frequency coupling?

Mária Orendáčová ^* Eugen Kvasnak

• Third Faculty of Medicine, Charles University, Prague, Czechia

In recent years, the dynamics and function of cross-frequency coupling (CFC) in the EEG has become a widely investigated research topic. One possible way to study CFC is to apply non-invasive neuromodulation methods such as transcranial alternating current stimulation (tACS) and neurofeedback (NFB). We address 1) the potential applicability of single and multifrequency tACS and NFB protocols in CFC research; 2) the prevalence of different types of CFC, such as phaseamplitude or amplitude-amplitude CFC, in tACS and NFB studies; 3) factors that contribute to interand intra-individual variability in CFC and ways to potentially address them. Here we analyzed research studies on CFC, tACS and neurofeedback. Based on current knowledge, different types of CFC have been reported in tACS and NFB studies. We hypothesize that CFC can be induced by direct and indirect effects of tACS and neurofeedback. Several variability factors such as health status, age, fatigue, personality traits, and closed vs. open eye state may influence the types of CFCs. Modifying the duration of the tACS and neurofeedback intervention and selecting a specific demographic experimental group could reduce these sources of CFC variability. Neurofeedback and tACS appear to be promising tools for the study of CFC.