The effects of non-invasive brain stimulation on sleep disturbances among different neurological and neuropsychiatric conditions: A systematic review

Sleep disturbances (e.g., difficulty to initiate or maintain sleep) and poor sleep quality are major health concerns that accompany several neurological and neuropsychiatric clinical conditions where different brain circuitries are affected (e.g., chronic pain, Parkinson's disease or depression), having a great impact in the individual's well-being, quality of life, and the socioeconomic system. Sleep disturbances in absence of breathing or neurological disorders are mainly treated with medications (e.g., benzodiazepines, hypnotics, etc.) and cognitive behavioral therapy, which are associated with side-effects and adherence issues, respectively. Moreover, these therapies do not seem to work effectively for some individuals. Repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are non-invasive stimulation techniques used to treat several conditions and symptoms. Results from this systematic review indicate that rTMS and tDCS are safe and have potential to improve insomnia symptoms and sleep disturbances across different types of neurological and neuropsychiatric diseases. However, uncontrolled and quasi experimental studies with high risk of bias were included. Thus, although these results can help developing the field, caution in interpreting them is advised. Additional research efforts are needed to reduce bias, improve quality, and characterize optimal brain stimulation parameters to promote their efficacy on sleep related outcomes.