Binaural beats to entrain the brain? A systematic review of the effects of binaural beat stimulation on brain oscillatory activity, and the implications for psychological research and intervention - PMC

Systematic Review of Binaural Beat Stimulation and Brainwave Entrainment

• Definition: Binaural beats are an auditory illusion created when two different frequencies are presented separately to each ear, resulting in the perception of a third tone oscillating at the difference frequency.
• Key Constraints:
  • Carrier Frequency: Best perceived at carrier frequencies around 400 Hz; maximum carrier frequency is 1000 Hz.
  • Frequency Difference: The difference between the two tones must be below 30 Hz.
  • Perception Thresholds: Differences < 3 Hz are perceived as a rotating tone; 3–20 Hz as a fluctuating loudness; > 20 Hz as a rough sound.
• Neurobiology: The superior olivary complex (SOC) is the primary brain structure responsible for processing these phase differences.
• Brainwave Entrainment (BWE) Hypothesis: The theory that external stimulation at a specific frequency causes the brain’s electrocortical activity to oscillate at that same frequency.
• Systematic Review Findings:
  • A review of 14 studies found highly inconsistent results.
  • 5 studies supported the BWE hypothesis, 8 reported contradictory results, and 1 reported mixed results.
• Methodological Issues: The field suffers from significant heterogeneity in experimental design, implementation of binaural beats, and EEG analysis parameters, which limits the comparability of research.
• Conclusion: There is a critical need for standardized research approaches to determine the actual efficacy of binaural beats for psychological and cognitive interventions.
• Distinction: Binaural beats (processed via phase differences in the brain) are distinct from monaural beats (physical interference of sound waves at the cochlear level).