Effect of Transcranial Alternating Current Stimulation (tACS) on Serotonin-1A Receptor in Patients With Major Depressive Disorder

5-HT1A receptor appears to be significantly involved in the effectiveness of electroconvulsive therapy (ECT). Like alternating current in ECT, tACS also applies alternating current to intervene in neuropsychiatric disorders. We previously found that tACS with large current, such as 15 mA, via the forehead and bilateral mastoids can improve depressive symptoms. However, the underlying mechanism of 15 mA tACS in depression remains unclear. We propose a scientific hypothesis that 15 mA tACS may increase hippocampal 5- HT1A receptors, then to reduce depression in depressive patients. Meanwhile, 15 mA tACS may increase the whole-brain functional connectivity with the hippocampus as the seed point. This study will utilize a multimodal data through 18F-MPPF PET/MR, including MPPF metabolism, resting-state fMRI, DTI, and 3D-T1 structural images. By observing the alterations of 5-HT1A receptor and the functional network between MDD patients and healthy controls, and between the pre- and post-tACS intervention in MDD patients, our aims to explore the effect of tACS on the serotonergic system in depression.