This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages)(Learn how and when to remove this template message)
Brainwave entrainment, also referred to as brainwave synchronization and neural entrainment, refers to the hypothesized capacity of the brain to naturally synchronize its brainwave frequencies with the rhythm of periodic external stimuli, most commonly auditory, visual, or tactile.
It is believed that patterns of neural firing, measured in Hz, correspond with states of alertness such as focused attention, deep sleep, etc. It is hypothesized that by listening to these beats of certain frequencies one can induce a desired state of consciousness that corresponds with specific neural activity, such as studying, sleeping, exercising, meditating, doing creative work, and so on.
Neural oscillation and electroencephalography (EEG)
Neural oscillations are rhythmic or repetitive electrochemical activity in the brain and central nervous system. Such oscillations can be characterized by their frequency, amplitude and phase. Neural tissue can generate oscillatory activity driven by mechanisms within individual neurons, as well as by interactions between them. They may also adjust frequency to synchronize with the periodic vibration of external acoustic or visual stimuli.
The activity of neurons generate electric currents; and the synchronous action of neural ensembles in the cerebral cortex, comprising large numbers of neurons, produce macroscopic oscillations. These phenomena can be monitored and graphically documented by an electroencephalogram (EEG). The electroencephalographic representations of those oscillations are typically denoted by the term 'brainwaves' in common parlance.
The technique of recording neural electrical activity within the brain from electrochemical readings taken from the scalp originated with the experiments of Richard Caton in 1875, whose findings were developed into electroencephalography (EEG) by Hans Berger in the late 1920s.
Neural oscillation and cognitive functions
The functional role of neural oscillations is still not fully understood; however they have been shown to correlate with emotional responses, motor control, and a number of cognitive functions including information transfer, perception, and memory. Specifically, neural oscillations, in particular theta activity, are extensively linked to memory function, and coupling between theta and gamma activity is considered to be vital for memory functions, including episodic memory.
Meaning and origin of the term 'entrainment'
Entrainment is a term originally derived from complex systems theory, and denotes the way that two or more independent, autonomous oscillators with differing rhythms or frequencies, when situated in a context and at a proximity where they can interact for long enough, influence each other mutually, to a degree dependent on coupling force, such that they adjust until both oscillate with the same frequency. Examples include the mechanical entrainment or cyclic synchronization of two electric clothes dryers placed in close proximity, and the biological entrainment evident in the synchronized illumination of fireflies.
Entrainment is a concept first identified by the Dutch physicist Christiaan Huygens in 1665 who discovered the phenomenon during an experiment with pendulum clocks: He set them each in motion and found that when he returned the next day, the sway of their pendulums had all synchronized.
Such entrainment occurs because small amounts of energy are transferred between the two systems when they are out of phase in such a way as to produce negative feedback. As they assume a more stable phase relationship, the amount of energy gradually reduces to zero, with systems of greater frequency slowing down, and the other speeding up.
Subsequently, the term 'entrainment' has been used to describe a shared tendency of many physical and biological systems to synchronize their periodicity and rhythm through interaction. This tendency has been identified as specifically pertinent to the study of sound and music generally, and acoustic rhythms specifically. The most ubiquitous and familiar examples of neuromotor entrainment to acoustic stimuli is observable in spontaneous foot or finger tapping to the rhythmic beat of a song.
Brainwaves, or neural oscillations, share the fundamental constituents with acoustic and optical waves, including frequency, amplitude and periodicity. Consequently, Huygens' discovery precipitated inquiry into whether or not the synchronous electrical activity of cortical neural ensembles might not only alter in response to external acoustic or optical stimuli but also entrain or synchronize their frequency to that of a specific stimulus.
Brainwave entrainment is a colloquialism for 'neural entrainment', which is a term used to denote the way in which the aggregate frequency of oscillations produced by the synchronous electrical activity in ensembles of cortical neurons can adjust to synchronize with the periodic vibration of an external stimuli, such as a sustained acoustic frequency perceived as pitch, a regularly repeating pattern of intermittent sounds, perceived as rhythm, or of a regularly rhythmically intermittent flashing light.
- Fredricks, R. (2008). Healing and Wholeness: Complementary and Alternative Therapies for Mental Health. All Things Well Publications/AuthorHouse. p. 120. ISBN 978-1-4343-8336-5. Retrieved April 5, 2017. and
- Cantor, David S.; Evans, James R. (2013-10-18). Clinical Neurotherapy: Application of Techniques for Treatment. Academic Press. ISBN 9780123972910.
- Niedermeyer E. and da Silva F.L., Electroencephalography: Basic Principles, Clinical Applications, and Related Fields. Lippincott Williams & Wilkins, 2004.
- da Silva FL (1991). "Neural mechanisms underlying brain waves: from neural membranes to networks". Electroencephalography and Clinical Neurophysiology. 79 (2): 81–93. doi:10.1016/0013-4694(91)90044-5. PMID 1713832.
- Cooper R, Winter A, Crow H, Walter WG (1965). "Comparison of subcortical, cortical, and scalp activity using chronically indwelling electrodes in man". Electroencephalography and Clinical Neurophysiology. 18 (3): 217–230. doi:10.1016/0013-4694(65)90088-x. PMID 14255050.
- Llinas, R. R. (2014). "Intrinsic electrical properties of mammalian neurons and CNS function: a historical perspective". Front Cell Neurosci. 8: 320. doi:10.3389/fncel.2014.00320. PMC 4219458. PMID 25408634.
- Fries P (2005). "A mechanism for cognitive dynamics: neuronal communication through neuronal coherence". Trends in Cognitive Sciences. 9 (10): 474–480. doi:10.1016/j.tics.2005.08.011. PMID 16150631. S2CID 6275292.
- Fell J, Axmacher N (2011). "The role of phase synchronization in memory processes". Nature Reviews Neuroscience. 12 (2): 105–118. doi:10.1038/nrn2979. PMID 21248789. S2CID 7422401.
- Schnitzler A, Gross J (2005). "Normal and pathological oscillatory communication in the brain". Nature Reviews Neuroscience. 6 (4): 285–296. doi:10.1038/nrn1650. PMID 15803160. S2CID 2749709.
- Buszaki G (2006). Rhythms of the brain. Oxford University Press.
- Nyhus, E; Curran T (June 2010). "Functional role of gamma and theta oscillations in episodic memory". Neuroscience and Biobehavioral Reviews. 34 (7): 1023–1035. doi:10.1016/j.neubiorev.2009.12.014. PMC 2856712. PMID 20060015.
- Rutishauser U, Ross IB, Mamelak AN, Schuman EM (2010). "Human memory strength is predicted by theta-frequency phase-locking of single neurons" (PDF). Nature. 464 (7290): 903–907. Bibcode:2010Natur.464..903R. doi:10.1038/nature08860. PMID 20336071. S2CID 4417989.
- Néda Z, Ravasz E, Brechet Y, Vicsek T, Barabsi AL (2000). "Self-organizing process: The sound of many hands clapping". Nature. 403 (6772): 849–850. arXiv:cond-mat/0003001. Bibcode:2000Natur.403..849N. doi:10.1038/35002660. PMID 10706271. S2CID 4354385.
- Pantaleone J (2002). "Synchronization of Metronomes". American Journal of Physics. 70 (10): 992–1000. Bibcode:2002AmJPh..70..992P. doi:10.1119/1.1501118.
- Bennett, M., Schatz, M. F., Rockwood, H., and Wiesenfeld, K., Huygens's clocks. Proceedings: Mathematics, Physical and Engineering Sciences, 2002, pp563-579.
- Will, U., and Berg, E., "Brainwave synchronization and entrainment to periodic stimuli" Neuroscience Letters, Vol. 424, 2007, pp 55–60.
- Cade, G. M. and Coxhead, F., The awakened mind, biofeedback and the development of higher states of awareness. New York, NY: Delacorte Press, 1979.
- Neher, A., "Auditory driving observed with scalp electrodes in normal subjects. Electroencephalography and Clinical Neurophysiology, Vol. 13, 1961, pp 449–451.
- Zakharova, N. N., and Avdeev, V. M., "Functional changes in the central nervous system during music perception. Zhurnal vysshei nervnoi deiatelnosti imeni IP Pavlova Vol. 32, No. 5, 1981, pp 915-924.
- Will U, Berg E (31 August 2007). "Brain wave synchronization and entrainment to periodic acoustic stimuli". Neuroscience Letters. 424 (1): 55–60. doi:10.1016/j.neulet.2007.07.036. PMID 17709189. S2CID 18461549.
- Kitajo, K.; Hanakawa, T.; Ilmoniemi, R.J.; Miniussi, C. (2015). Manipulative approaches to human brain dynamics. Frontiers Research Topics. Frontiers Media SA. p. 165. ISBN 978-2-88919-479-7.
- Thaut, M. H., Rhythm, Music, and the Brain: Scientific Foundations and Clinical Applications (Studies on New Music Research). New York, NY: Routledge, 2005.
- Berger, J. and Turow, G. (Eds.), Music, Science, and the Rhythmic Brain : Cultural and Clinical Implications. New York, NY: Routledge, 2011.