Non-Invasive Brain Stimulation for Insomnia - A Review of Current Data and Future Implications

Abstract

Neuroimaging evidences point to the role of hyperarousal in the pathophysiology of insomnia. While actual treatments fail to directly target brain hyperarousal, emergent complementary therapies known as neuromodulation techniques aim to improve sleep in people with insomnia by targeting irregularities in their brain activity. In this paper, we narratively review the most relevant studies reporting the application of neuromodulation techniques to improve sleep in individuals with insomnia. Using a non-systematic approach, we retrieved relevant literature across health-related bibliographic databases. Studies were included if they specifically assessed the effects of a neuromodulation technique on sleep in a sample of patients with insomnia. Three studies on transcranial direct current stimulation (tDCS) and six studies on repetitive transcranial magnetic stimulation (rTMS) were retained. No study on transcranial alternating current stimulation (tACS) was found. Preliminary data on tDCS in a sample of individuals with insomnia shows that targeting frontal regions may have a positive impact on sleep. Findings of rTMS studies, especially 1-Hz low-frequency stimulation, suggest that it improves objective and subjective sleep in individuals with insomnia. Nonetheless, in both neuromodulation techniques, significant variability was found between stimulation parameters, study samples, and sleep outcomes. Although evidence on the impact of neuromodulation for insomnia remains scarce, recent data suggest it may have a sleep-deepening effect. Based on this review, and the limitations indicated by authors of included studies, we urge researchers to promote this field of research by testing different stimulation parameters, replicating already existing protocols, or adding standardized sleep-related outcomes.