Search terms used to describe brainwave entrainment and psychological outcomes were used to search major databases for peer reviewed articles. Experimental and quasi-experimental studies were accepted. Case studies were excluded. Eighteen published studies that satisfied our criteria included cognitive outcomes, relief of stress and anxiety, mood enhancement, relief of pain, migraines and pre-menstrual syndrome. All published studies reported positive outcomes using either auditory (4) or photic stimulation (12), and/or audio visual entrainment (AVE) (5), within frequencies hypothesized to have positive effects.

Introduction:
Brainwave entrainment is a multi-million dollar business, and many companies are selling CDs and other devices designed to enhance cognitive functioning, relieve stress, improve mood, alleviate pain and much more.

Objective:
To compile a comprehensive review of the literature from peer reviewed journals on the psychological effects in brainwave entrainment research.

Methods
A comprehensive list of search terms used to describe brainwave entrainment and psychological outcomes were used to search major databases such as OVID, Psych Info, Medline, EBSCO, Social and Behavioral Collections and Scopus. Experimental and quasi-experimental studies were accepted. Case studies were excluded.

Results
18 published studies that satisfied our criteria included the psychological outcomes of enhanced attention, memory, overall improvement in intelligence and reading ability, relief of stress and anxiety, mood enhancement, relief of pain, migraines and pre-menstrual syndrome (PMS). 8 studies examined short term single session effects, 8 examined longer term multiple session effects and 2 examined both. All published studies reported positive outcomes using either auditory (4) or photic stimulation (12), and/or audio visual entrainment (AVE) (5), within frequencies hypothesized to have positive effects.

Conclusion
Preliminary studies suggest that brainwave entrainment has positive effects on relieving psychological symptoms as evidenced by statistical analyses from both experimental and quasi-experimental data. However, there were limitations to the existing literature. Most studies had small sample sizes and only 13 studies had control groups. Future studies should aim to compare entrainment modalities and the effects of different frequencies, and need proper controls.