Can Music Be Used To Entrain Deep Sleep Brainwaves Improving Sleep Quality, Exercise Recovery, or Cardiac Health?
Sleep & Brainwaves
We can define Sleep as a brain state, a process or behaviour. The brain state consists of wave-like formations that contribute to various stages of sleep, with each stage playing a unique role in our health and recovery . We can measure brainwave activity using a technique called Electroencephalogram (EEG). Scoring sleep stages uses EEG by analysing waveform amplitude and frequencies within the brain by placing electrodes on the head and face areas. Through the use of EEG, we can see there are two phases of sleep. Non-REM & REM Sleep. Within NREM sleep, three different stages comprising of dominant brainwave forms. Wakefulness and relaxation consist of Alpha waves, and when drifting into stage N1 or deep relaxation, Theta waves occur. The following stage is N2, dampening down activity in the reticular activating system, rendering people unconscious. N2 is distinguishable because it includes the appearance of Sleep Spindles and K Complexes alongside Theta waves. These complexes look like more significant bursts of electrical activity, thought to be associated with the formation of memories and to prevent arousal through habituation of environmental sounds . Stage 3, known as deep sleep, consists of large-amplitude, low-frequency waves call Delta waves. On to the second phase of sleep, namely REM sleep, the waveform is similar to wakefulness. It consists of high-frequency, low amplitude waves; however, there is also measurable low muscular tension, if any, corresponding with that rapid eye movements.
Autonomic Nervous System Function During Sleep
Research suggests that sleep, especially NREM sleep, is one of the most significant contributors to parasympathetic nervous activity (PSA) . PSA is associated with increased nutritional absorption, immune responses that support anti-inflammatory benefits, and recovery from exercise [4, 5, 6]. Heart rate variability (HRV) measures the variation between heartbeat interval lengths caused by a fluctuation in autonomic nervous activity. Reflex responses from changes in intra-thoracic pressures during breathing create these HRV variations, a phenomenon known as respiratory sinus arrhythmia. During inspiration, baroreceptors detect stretching and pressure within the lungs. Increased thoracic pressure during inspiration promotes the sympathetic nervous activity (SNA) associated with stress and excitation for wakefulness. While expiration stimulates PNA. Image a pendulum swinging, one side of the nervous system excites the brain and body, and the other acts as an inhibitory mechanism. ANS activity depends on which side the pendulum is swinging, and thus through specific breath work or changing the breath cycle, we can create shifts in SNA and PNA dominance. The alterations in breathing and therefore changes in the pendulum of the ANS either create high-frequency oscillations or low-frequency oscillations, shifting variances in heart rate. High-frequency oscillations are associated with the PNA and can effectively measure such activity when unnaturally breathing alterations do not coincide, such as during vocal response —as such, measuring HRV-HF during sleep may provide accuracy in PNS activity. Throughout the phases of sleep, we observe different frequencies of oscillations. For example, in Stage 3 deep sleep, HF is more dominant, thus making it that state of sleep largely PNA dominate, whereas REM sleep comprises SNA dominance .
Brainwave Entrainment and Sleep
Scientific literature suggests that we can purposely alter brainwaves through meditation, with studies identifying that Theta waves are often seen in stage 1 and 2 sleep appear across the front and hindbrain in active meditators . Music also has a similar impact on brainwave forms. As a collective, those who attend music festivals are likely to have similar brainwave activity while listening to music . The music and atmosphere put everyone on the same wavelength creating a feeling of euphoria through activation of the nervous system, releasing happy chemicals such as dopamine and serotonin . These moments could be described as somewhat a spiritual experience and is why music has played a significant role in religious and shamanic practices for thousands of years. It has demonstrated that we can use music to entrain brainwaves by using beats composed of different frequencies repetitively, known as binaural beats, entraining differing wavelength forms within the brain.
However, can this be done during sleep?
In a 2014 pilot study by Allen et al., brainwave entrainment was used in soccer players to alter sleep states to enhance recovery. Athletes reported improved sleep quality and morning alertness, concluding it is worth further research . We have to question whether it is possible to enhance recovery by using binaural beats similar to the brainwave frequency during deep or REM sleep, thus increasing the percentage of deep sleep associated with physical and mental recovery.
Perhaps by using binaural beats through music that consists of more delta waveform frequencies, we can entrain the brain so that deep sleep stages are extended, increasing HF-related HRV and thus PNS dominance. Deep sleep releases up to 70% of our growth hormone . Growth hormone-stimulated the release of insulin-like growth factors, specifically IGF-1. IGF-1 plays a significant role in activating the mTOR pathway regulating satellite cell activity . Satellite cells initiate the repair process associated with muscular hypertrophy. Therefore it is hypothesised that with the use of binaural beats during sleep, there may be some evidence to suggest we can enhance recovery from exercise and potentiate muscular hypertrophy. In addition, increasing HRV is thought to be related to improving cardiovascular function specifically the baroreflex sensitivity which aids in blood pressure regulation and distribution, and therefore, by using specific music or sounds, we may even be able to improve overall cardiovascular health.
On review of the current data, one study by Lazic and Ogilvie  explored music embedded with a pulse between the 0.5 – 3.5Hz range. This range is a similar frequency range as Delta activity which is associated with deep sleep. The exogenous stimulus increased delta power in the right hemisphere during the sleep onset period for the music condition but not for tones or silence. No significant difference was found for any of the polysomnography measures during sleep. Participants responses to whether an intervention helped sleep resulted in no significant difference between the tones and music. The delta embedded music encouraged brainwave entrainment but did not improve self-report or physiological measures of sleep onset length or physiological measures of sleep quality compared to control or tones.
With that said, it offers no evidence to suggest that we can increase stage 3 sleep by using music or beats; however, in a review by Dickson & Schubert , they found support for using music for masking out environmental noise, which improved sleep quality. The relaxation reported measures had mixed levels of support ranging from strong suggestion to no effect for measures of sleep quality and sleep onset latency. Enjoyment and distraction vary widely from opposing support (i.e. inhibiting rather than supporting sleep) to a statistically demonstrable positive relationship. The expectation had possible support across physiological and self-report measures and entrainment varied from possible support to no effect. Providing us with a bag of mixed results.
Therefore, whilst EEG entrainment may not be a method that we have evidence to say it improves sleep quality and promotes other parasympathetic activity just yet. For individuals who struggle to sleep following competition, have disturbed sleep or suffer from primary insomnia. It may well be beneficial to use binaural beats or relaxing music to help aid in sleep onset, thus helping with further recovery from exercise, improving overall performance. Based on the current data we cannot suggest that entraining deeper sleep brainwaves improves sleep quality, exercise recovery, or cardiac health. However, it seems plausible to create further randomised control trials with tighter methodological approaches to investigate the possibility.
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