High-frequency neurostimulation of the right inferior parietal cortex alters the sense of agency: results from tACS/tRNS and rTMS-EEG studies

Background: Sense of agency (SoA) is the subjective experience of causing and controlling one’s actions. Recent studies suggested that SoA can be influenced by external manipulation through neurostimulation methods, while others have linked it to gamma oscillations in the right inferior parietal lobule (IPL). Objective: This study aims to provide evidence for a causal role of the right IPL in SoA using multiple noninvasive brain stimulation methods (NIBS), electroencephalography (EEG), and a feedback manipulation task. Methods: In two experiments, we investigated the effect of gamma band (60 Hz) transcranial alternating current stimulation (tACS), transcranial random noise stimulation (tRNS), low-frequency (1 Hz) repetitive transcranial magnetic stimulation (rTMS), and high-frequency (10 Hz, 20 Hz) rTMS over the right IPL.Results: As anticipated, gamma band tACS and high-frequency rTMS had distinct effects on SoA. Gamma band tACS enhanced the detection of non-self agency, while high-frequency rTMS impaired this capacity and reduced the overall SoA. EEG spectral analysis confirmed the impact of stimulation on the right IPL and highlighted the role of beta band oscillations.Conclusion: Using the largest subject pool to date, our study provides causal evidence for the crucial role of the right IPL in processing SoA, particularly in detecting non-self agency arising from real-time sensorimotor mismatch comparison. Our findings suggest that external stimulation affects the comparator mechanism, rather than introducing prediction errors as previously proposed, and support the view that the right IPL is more closely associated with the implicit feeling of agency rather than with higher cognitive processes.