Transcranial alternating current stimulation in subjects with insomnia symptoms: A randomized, double-blind and controlled study

Background: This study evaluated whether transcranial alternating current stimulation (tACS), a non-invasive brain stimulation technique, could alleviate insomnia symptoms. Methods: Participants exhibiting insomnia symptoms without meeting the criteria for insomnia disorder were recruited and randomized into 0.5 Hz, 100 Hz, or a sham group. To maximize the delivery of intracranial stimulation, a carrier frequency of 10 kHz was utilized. Participants were required to use the device for 30 min, twice daily for six weeks. Results: Eighty-seven participants (74 females, mean age = 54.15 +/- 0.73 years) were randomized and completed the trial. The Insomnia Severity Index scores showed significant improvement across all three groups without a significant difference between groups (sham: 13.83 to 8.45, p < 0.05; 0.5 Hz: 12.03 to 8.79, p < 0.05; 100 Hz: 12.38 to 7.83, p < 0.05). In the average sleep diary over four days, sleep latency (SL) and wake after sleep onset (WASO) decreased in all three groups (sham, 0.5 Hz, 100 Hz) without significant group by visit interaction (SL: -5.74 min, -8.94 min, -16.53 min, respectively, p = 0.345; WASO: -10.74 min, -23.62 min, -16.73 min, respectively, p = 0.431). No significant improvements were observed in actigraphy-based sleep measures. Conclusions: tACS did not demonstrate greater efficacy than sham treatment in ameliorating symptoms of insomnia. Future studies should account for the potent placebo effect on sleep and the potential for high carrier frequencies to obscure the target frequencies.