Comparisons of transcranial alternating current stimulation and repetitive transcranial magnetic stimulation treatment therapy for insomnia: a pilot study

To the editor: Insomnia disorder has a serious and widespread detrimental effect on humans with comorbidity with other mental or physical health problems.1 2 In recent years, non-invasive brain stimulation (NIBS) techniques, especially transcranial magnetic stimulation (TMS) and transcranial electrical stimulation, have been increasingly used for the treatment of brain diseases, including insomnia disorder. Low-frequency repetitive transcranial magnetic stimulation (rTMS) has been proven to reduce neuronal excitability to modulate the abnormal hyperarousal of patients with insomnia. The efficacy of rTMS for insomnia has been observed, and rTMS may be a safe and effective option for insomnia treatment.3 However, the stimulation effects of rTMS have varied substantially across studies and individuals. rTMS was found to produce region-specific effects that critically depend on the connectivity profile of target regions, and an extended, trans-scale model has been developed.4 Unfortunately, it could not simply generalise across different protocols, which hindered the development of more precise and effective regulation for brain abnormalities. A previous review indicated that dorsolateral prefrontal cortex (DLPFC) stimulation by rTMS could modulate the release of key neurotransmitters in the sleep–awake cycle. Even though the proposed mechanisms were still speculative, the review indicated that the stimulation of DLPFC (right, left and bilaterally) with low frequencies (1 Hz) could improve sleep architecture and quality.5 Continued research into better rTMS protocols for treating insomnia disorder and further study of the mechanisms of efficacy were still warranted. It is also worth noting that transcranial alternating current stimulation (tACS) has received much attention in recent years. tACS was able to modulate neural oscillations of specific frequencies through entrainment.6 Such frequency specificity facilitated the precise modulation of the brain, leading to a better therapeutic effect. Currently, tACS has been showing results for initial sleep regulation and insomnia treatment.7 8 Since the role …