A comprehensive review of the psychological effects of brainwave entrainment

OBJECTIVE: Brainwave entrainment (BWE), which uses rhythmic stimuli to alter brainwave frequency and thus brain states, has been investigated and used since the late 1800s, yet many clinicians and scientists are unaware of its existence. We aim to raise awareness and discuss its potential by presenting a systematic review of the literature from peer-reviewed journals on the psychological effects of BWE. DATA SOURCES: Terms used to describe BWE and psychological outcomes were used to search English language studies from OVID Medline (1950-2007), Psychlnfo (1806-2007), and Scopus. STUDY SELECTION: Twenty studies selected satisfied the following criterion: studies needed to use rhythmic stimuli with the aim of affecting psychological outcomes. Peer-reviewed experimental and quasi-experimental studies were accepted. Case studies and review articles were excluded. Psychological outcomes were measured using standard assessment methods or as deemed appropriate by peer review. DATA EXTRACTION: Other clinical measurements, including electroencephalogram response, galvanic skin response, and neurotransmitter levels were not induded. DATA SYNTHESIS: Psychological outcomes addressed cognition, stress and anxiety, pain relief, headaches or migraines, mood, behavior, and premenstrual syndrome (PMS). Protocols included the use of single, alternating, ascending, or descending frequencies or were determined by the subject, using auditory and/or photic stimulation. Studies examined single session effects and/or longer-term multiple session effects. CONCLUSIONS: Findings to date suggest that BWE is an effective therapeutic tool. People suffering from cognitive functioning deficits, stress, pain, headache/migraines, PMS, and behavioral problems benefited from BWE. However, more controlled trials are needed to test additional protocols with outcomes.