Modulating Default and Salience/Ventral Attention networks: Exploring the treatment effect of transcranial alternating current stimulation on chronic insomnia

Chronic insomnia necessitates novel therapeutic strategies. While transcranial alternating current stimulation (tACS) shows promise, its neural mechanisms remain elusive. We conducted a 4-week, double-blind, randomized, sham-controlled trial to investigate the effects of high-intensity tACS (15 mA). Eighteen patients completed the protocol and longitudinal resting-state fMRI. Clinical results demonstrated a significant reduction in Pittsburgh Sleep Quality Index (PSQI) scores within the active tACS group [13.8 (3.0) vs. 7.7 (3.0), p < 0.001], indicating substantial clinical improvement, whereas the sham group showed no significant change [13.8 (2.9) vs. 13.9 (2.4), p = 0.74]. Furthermore, the spontaneous brain activity exhibited extensive reductions in both the Default and Salience/Ventral Attention networks, showing a negative correlation with increase in clinical sleep scores. The functional connectivity was significantly altered within the Default and Salience/Ventral Attention networks, and the majority of changes displayed a decreasing trend. Graph theoretical analysis revealed a topological reorganization in these networks, characterized by reduced clustering coefficients and characteristic path lengths, coupled with increased global efficiency. The study provides valuable insights into the potential mechanisms of tACS as an innovative intervention for improving sleep quality in insomnia, contributing to further research and optimization for insomnia treatment.