What is Bilateral Music Stimulation?
Introduction
What can bilateral music stimulation help with and what does the research say about it? Are there findings that support the claims made in various playlists? Is bilateral music the same as binaural music? There are so many playlists on Spotify, YouTube and TikTok at the moment with this title. What is this type of music and does it really do what it says it does? I took a look at the data.
Who am I and why am I talking about this?
I am currently studying for a MMus in Music & Sound at the Academy of Music and Sound via the London College of Music at the University of West London. As part of my Masters research project I wanted to focus on bilateral music stimulation. I am a therapist by background and am curious about how music is being used functionally to assist with various cognitive, emotional and somatic factors. In my trauma practice as an EMDR and Brainspotting therapist I have used bilateral sound to assist clients in processing emotional memories. But I have often wondered about what exactly is happening when clients listen to this type of sound. How does it work, what does it do? In my blog posts I aim to share what I find as I navigate this fascinating area.
The title that you will usually see is something like, ‘Bilateral Music Stimulation’ and it will often mention what it can help with in the title, for example “Bilateral Music Stimulation for ADHD’. As there are so many of these playlists, I thought there must be research showing these benefits and I was fascinated to dive in and find out who was studying this area and what they found.
What does the research say about bilateral music stimulation?
This completely perplexed me but on my initial searches (in July 2023), I could find NO research to support claims made for ‘bilateral music stimulation’ for ADHD, Attention, Memory, or Relaxation. In fact, there was no study that specifically looked at multipart (a piece of music rather than a single bleep or tone) bilateral music for any of these areas.
What? No research at all for the effectiveness of bilateral music stimulation?
This is where is gets a little confusing. There IS research for binaural beat stimulation, and alternating auditory bilateral stimulation as used in EMDR therapies. Because of this I felt I needed to dive deeper into these two areas to try and understand more about bilateral stimulation. I looked first at how it is used in EMDR therapy.
Bilateral Stimulation and EMDR Therapy
In a therapy known as Eye Movement Desensitisation and Reprocessing Therapy (EMDR), a client is asked to think of a specific distressing image or notice a distressing feeling or thought whilst engaging in bilateral stimulation (BLS). The type of BLS used can differ from following a therapist’s fingers with your eyes or following a light moving horizontally left to right (Visual BLS), to tapping alternate knees or shoulders or feeling the buzz of a tactile unit in each palm (Tactile, or Somatic BLS). It can also involve listening to a single tone through headphones that appears to move from the left to right ear in an alternating pattern that can vary in speed and amplitude (Auditory BLS).
The application of the BLS usually occurs in short sets. A ‘set’ is a movement from left to right and back again, or vice versa. For example, a tone in the right ear then the left ear and then back to the right ear would be one ‘set’. After approximately 8-36 sets, the therapist will then pause to ask the client what they notice, before resuming another set. This process continues for 30-60 minutes or until the client reports a reduced level of distress. The level of distress is measured in units called ‘SUDS’ and this ‘subjective unit of distress’ (SUD) is usually rated between 0-10 (Shapiro, 2001; Calancie et al., 2018).
A study of the different types of BLS (tactile, visual, or auditory) has indicated that they show equal effectiveness in EMDR therapy (Servan-Schreiber et al., 2006), and so the choice of mode is more dependent on patient and therapist preference. The importance of the stimulation being alternate, rather than continuous or intermittent was evidenced by Servan-Schreiber et al’s (2006) randomised trial of stimulation type. This study built on previous work that had also found a superior result for alternating rather than continuous stimulation (Servan-Schreiber et al., 2006). This means that the presentation of the sound, the touch and the visual eye movements is more effective when it moves left to right and right to left, than if the touch/taps occur at the same time on the body, or the tones occur at the same time to each ear.
The BLS that is used in EMDR Therapy is a tool for processing a specific emotion within the context of the safety of therapy. It has been shown to be effective in the processing of fear (Herkt et al., 2014) and the distress associated with traumatic memories (Servan-Schreiber et al., 2006). Could it also be used in non-clinical populations for a less defined emotion, and could it have the same therapeutic effect? It seems that this is what bilateral music playlists on Spotify are being used for.
Some of the playlist’s state that the music is ‘beat stimulation music’. Is this different to bilateral music?
Auditory beat stimulation
Auditory beat stimulation is the presentation of slightly different frequencies, via a single tone of stable amplitude either to both ears simultaneously (monoaural) or to each ear independently (binaural). For example, a 400Hz tone and a 6Hz tone delivered to each ear at the same time, via headphones would be a monaural beat condition, whereas a 400Hz tone delivered to one ear and then a 406Hz tone delivered to the other ear would be a binaural beat condition and would result in a binaural beat of 6Hz. In the binaural beat condition, each ear hears the tone delivered but because there is a difference between the two frequencies, the brain detects this difference and creates a new 6Hz ‘tone’ in virtual space in between each ear, this is called a binaural beat (Orozco Perez, Dumas and Lehmann, 2020).
In the binaural beat condition, the left and right hemispheres of the brain need to communicate to detect the phase difference and produce the imagined beat. This means that binaural beats can show different effects than monaural beats (Ingendoh, Posny and Heine, 2023). Whilst monaural beats can be perceived across the whole audible spectrum, binaural beats are said to be perceived only at low frequencies, between 1-30Hz (Ingendoh, Posny and Heine, 2023). However, there is some conflicting information here as some studies have reported an effect on focus and concentration with frequencies above 30Hz (Chaieb et al., 2017). The binaural beat effect for low frequencies occurs provided the ‘carrier’ frequencies are not above 1000Hz for each ear and the additional frequency delivered is not above 30Hz (Padmanabhan, Hildreth and Laws, 2005). It has been reported that there is a better response if frequencies between 400-500Hz are used (Padmanabhan, Hildreth and Laws, 2005).
The shift of brainwave activity into the perceived new beat is called ’entrainment’ (Engelbregt et al., 2021). This is where the brain shifts into a different pattern of brainwave activity. For example, a 12Hz binaural beat can entrain the brain into an Alpha brainwave state. Alpha brainwaves occur when the brain is in a relaxed but attentive state (Abhang, Gawali and Mehrotra, 2016). This is the type of state our brains are in whilst we are in creative states of mind. The brainwave range for Alpha waves is between 8-12Hz (Abhang, Gawali and Mehrotra, 2016).
It has been reported that this brainwave entrainment, either monoaurally or binaurally can have effects on cognition and mood state (Chaieb et al., 2015). In a study focused on monaural beat stimulation (MBS), (Chaieb et al., 2017) carried out an experimental study with three different frequencies (6 Hz Theta band, 10Hz Alpha band & 40Hz Gamma band). The aim of the study was to tease apart any differences between MBS and each frequency on mood and cognition. There were 25 participants (Male =12 Female = 13) and measures were taken of anxiety, emotion, memory, and vigilance before and after exposure to 15 minutes of MBS at each frequency. They found that there was a significant effect for all three beat conditions in terms of reductions in levels of state anxiety amongst participants.
In terms of other emotions, only 40Hz (Gamma) frequencies indicated a significant effect on feelings of sorrow, unhappiness, and sadness. There was no effect of other beat frequencies on mood. Interestingly these scores for unhappiness did not correlate with scores on a measure of depression (Beck Depression Inventory). This means that the subjects who scored higher for depression did not necessarily show a reduction in their feelings of unhappiness, sorrow, and sadness with the gamma band MBS. This perhaps indicates an effect on fleeting emotions that are not necessarily at a clinical level. There was no effect of beat stimulation on the vigilance tasks, and no significant effect of beat stimulation on working memory or long-term memory scores. This indicated that monaural beats potentially do not affect attention and memory.
A study of both BBS and MBS in contrast to pink noise (PN) by (Engelbregt et al., 2021) found that whilst there was no overall conclusive effect in the BBS condition, there was a trend indicating increased attentional performance in the BBS group who experienced 40Hz Gamma band binaural beats. This finding supports that of previous studies which indicated that Gamma band binaural beats can improve vigilance and attention (Engelbregt et al., 2021). However, this contrasts with the statement that binaural beats only occur at low frequencies up to 30Hz as clearly there is an effect that is taking place with Gamma band waves at 40Hz.
Ingendoh’s et al’s (Ingendoh, Posny and Heine, 2023) systematic review discussed the conflicting findings in BBS studies. Some of the possible reasons include the differing ways that the beats are administered in practice, the length of exposure, the listening conditions, the type of beat, the rhythm of the pulse, and the amplitude. It is also possible that individual differences and preferences could also play a role here too (Ingendoh, Posny and Heine, 2023). These inconclusive results mean that there is some uncertainty over which auditory beat stimulation condition is the most effective, monoaural beat stimulation (MBS) or binaural beat stimulation (BBS).
What is the difference between bilateral stimulation, binaural beat stimulation, and monaural beat stimulation?
As these terms do sound similar and have some similarities in the way they are administered and discussed, it feels important to be specific about the differences between them.
Monaural beat stimulation is the delivery of slightly different frequencies to the left and right ear at the same time, whereas binaural beats involve the delivery of a different frequency to each ear, and this creates the perception of a third tone (Orozco Perez, Dumas and Lehmann, 2020). In contrast, bilateral stimulation does not involve the use of different frequencies. It is the same tone or piece of music but is delivered in an alternating pattern to the left and right ear. The pulse may move from left to right and/or the volume as well.
One of the mechanisms that is often discussed in beat stimulation studies is that these beats ‘entrain’ the brain. In other words, our brains ‘couple’ with the pulse of the beats and our bodies can also couple with the beat and move in time to the pulse. This is also called ‘rhythmic entrainment’.
Rhythmic entrainment
Entrainment is the name given to the interaction between independent self-sustaining rhythmical systems, where one has an influence on the other to the point where their movements can synchronise with each other (Clayton, 2012). The type of entrainment that takes place with binaural beats is called ‘brainwave entrainment’ where the binaural beat is a rhythmical system operating at a certain frequency, which influences the brain’s electrocortical activity, such that the brainwaves oscillate at the same frequency as the perceived binaural beat (Ingendoh, Posny and Heine, 2023).
A meta-analysis by (Heard and Lee, 2020), found that rhythm engages a bilateral sensorimotor network of action in the brain and body. This indicates the importance of rhythm when it comes to entraining the brain and body to movement. This sensorimotor entrainment is also used therapeutically and is usually referred to as ‘rhythmic auditory entrainment’ (RAS).
Rhythmic auditory entrainment also called Rhythmic Auditory Stimulation (RAS) is where auditory rhythm patterns (sensory input) can entrain a physical response in the body (a motor response). This sensorimotor communication has been used in rehabilitation for stroke, traumatic brain injury, and other movement disorders such as Parkinson’s disease (Thaut, McIntosh and Hoemberg, 2015).
Hurley, Martens and Janata, (2014) studied movements made in response to perceived groove in music, a phenomenon that is called ‘sensorimotor coupling’. They found that music with more instruments is perceived as having more groove than music with fewer instruments. They also found that in music that has many different instruments, varying the introduction of those instruments can lead to a higher amount of perceived groove and sensorimotor coupling. This finding is interesting because it suggests that a rhythmic pulse does not need to remain the same when trying to effect entrainment. It also suggests that layers of instrumentation can be brought into the beat stimulation sounds, such that we do not necessarily have to use a single tone but can instead utilise multipart music in the beat stimulation studies. It potentially indicates that entrainment could be increased by using multipart music in beat stimulation conditions.
There is a type of multipart music that includes bilateral alternating pulses that appears to use these principles. It is called ‘Biolateral Music’ (Grand, 2013).
Biolateral music and ‘Wingwave’ Music
In Brainspotting therapy, a therapy that was created by Dr David Grand, the bilateral stimulation used is auditory. However, unlike in EMDR therapies the sound is not a single tone but multipart music that has been specifically composed for that purpose. Dr Grand has trademarked the term ‘Biolateral music’ for this format. As well as an alternating pulse it also has an alternating volume shift to each ear to enhance the bilateral alternating stimulation for the listener (Grand, 2013). To-date there have been no peer-reviewed research studies of this type of music and its effects, whether clinical or otherwise, so it is difficult to draw comparisons with the type of auditory BLS carried out in EMDR therapy.
The term ‘audio bilateral stimulation’ is also used in a coaching method called ‘Wingwave’ (Weiland, Schul and Klatt, 2022) which has been developed by Frank Weiland, a sports coaching professional. ‘Wingwave’ music is said to comprise an alternating bilateral pulse and multipart music. This is potentially a form of bilateral music stimulation however there is no available study or link to this music unless it is purchased from the creator. It is therefore difficult to analyse this music.
Functional music
All the beat stimulation conditions that have been mentioned could be categorised as ‘functional’ music. They have been created for a specific purpose rather than for their own sake as a creative work. While music for media and film could also be termed as functional music. This type of music is usually created to be in and of itself a creative work that supports another piece of work that it is to be synchronised with. For binaural and bilateral beat stimulation, this music has been created with the specific purpose of altering something in the brain and body of the listener. It shares similarities with music that has been created to encourage sleep, as well as with meditation music or music for relaxation (Aalborg University and Lund, 2021).
There has been considerable growth in the availability of music for specific purposes, and playlists created according to mood rather than genre. A news report recently documented the involvement of Universal Music Group (UMG) in this space. UMG has partnered with Endel, a company that creates functional music for sleep and focus, to create tracks that combine artists’ work and artificial intelligence into functional music for wellness (Murtagh-Hopkins, 2023).
What are some of the research findings for auditory BLS (Bilateral stimulation)?
A study by Kaminska et al, (Kaminska et al., 2020) had investigated the effects of BLS on stress however auditory bilateral stimulation was not used alone, it was combined with either tactile or visual stimulation. As a result, conclusions cannot be drawn as to the specific effect of auditory stimulation. The study did however find that stress reduction was apparent across all types of bilateral stimulation in combination with the study’s virtual reality application. This study also included multipart music in the bilateral condition, which brings it closer to a bilateral music condition than any of the studies included in the final analysis. All five remaining studies used single auditory tones.
Nieuwenhuis et al (2013) looked at memory retrieval and BLS. Interestingly though, they found that tactile and visual, but not auditory BLS led to enhancements in memory retrieval. The study explored connectivity between the left and right hemispheres of the brain and how this may assist with memory retrieval. If auditory stimulation does not play as strong a role as visual and tactile stimulation, then it is possible this is due to a difference in hemispheric connectivity. In contrast to these findings though, a study by Servan-Schreiber et al (Servan-Schreiber et al., 2006) found no difference between auditory and tactile stimulation in their study.
There was a study that looked at fear and BLS. Herkt et al (Herkt et al., 2014) explored a part of the brain that is involved in the processing of threat, the amygdala. Their study investigated whether there was a difference in activation levels in the amygdala when utilising alternating auditory stimulation whilst looking at either anxiety-inducing or disgusting stimuli. Their results indicated that in the alternating condition there was an increase in activation in the amygdala for negative stimuli. They discuss this finding as potentially indicating a role for BLS assisting with reintegrating difficult emotional information in a therapeutic setting such as within EMDR therapy.
The experience of fear was also the focus of research by Boukezzi et al ((Boukezzi et al., 2017). They investigated the effect of auditory alternating bilateral stimulation (AABLS) on the experience of fear in a sample of 18 adults. They found that the application of BLS assisted the participants to reduce their fear more quickly during tasks designed to help extinguish a fear response. BLS played an active part in reducing the fear response and affected the retrieval of fear memories. The findings indicate a specific role for AABLS in reducing negative emotions such as fear. This is a small study and therefore further results would be needed, preferably from randomised controlled trials.
Horst et al (2017) looked at panic disorder. Their study was a randomised controlled trial (the gold standard in quantitative research). The trial compared EMDR Therapy and CBT Therapy for panic disorder. This study used audio tones as the BLS condition for the subjects in the EMDR group. The published article did not indicate the type of tone used or how it was delivered (for example how loud or fast). The results indicated that participants improved in both CBT and EMDR therapy, therefore there was no increased benefit through using BLS. In the discussion the authors state that eye movements may have proved more effective, and they cite two studies (van den Hout et al., 2012; de Jongh et al., 2013) that have both indicated that auditory tones are not as effective at taxing working memory as eye movements. However, these studies looked at memory and BLS, not mood and BLS. It is possible that auditory BLS is inferior to eye movements when it comes to memory retrieval or recall but shows a benefit with the processing of an emotion. The Horst et al study is therefore unable to assist in drawing any conclusions as to the role of AABLS in mood states.
Another experimental study of EMDR therapy, by Rousseau et al (2020) set out to study the effect of BLS on the recall of fear-based memories and of the reduction of fear. Their participants were 38 adults with a mean age of 32.6 years (Male=25, Female=13). Participants had no previous psychiatric or neurological history. The participants were asked to lie in a supine position inside an MRI scanner with MRI-appropriate headphones on. They were then presented with different coloured shapes and backgrounds, such as a red circle on a black background, and in the experimental condition the shape was presented with an electric shock, designed to be unpleasant but not painful. The auditory BLS used was a large band tone, delivered via headphones at a frequency of 1Hz. Following their exposure to the shock they were then expecting a shock to happen when next presented with the shapes. To extinguish this fear, they were presented with the shapes, but no electric shock. In each of the conditions there was a group with or without auditory BLS. The study found that the areas of the brain that were activated in this task were areas related to functional connectivity, emotion processing, executive control, and multisensory integration. These findings indicated that the AABLS activated parts of the brain involved in connecting emotional salience and memory. Also, in the BLS condition there was an increase in activation of areas related to functional connectivity and multisensory integration. The authors report these findings as being indicative of the role of AABLS on helping to integrate emotional, sensory and memory related stimuli.
In the small selection of studies just mentioned there was no detailed information on the listening conditions, type of headphones, sound pressure levels, volume or amplitude, and type of tone used or for how long. It was a theme throughout that the BLS used was discussed in very little detail. Yet sound is a stimulus that can have many variations including how it is applied. As a result of the scant information about the delivery of the sound it was not possible to draw any conclusions as to what aspect of the sound may have been responsible for its effects.
What terms were used to describe bilateral music?
In the peer-reviewed research studies that I investigated there were no studies that described or defined ‘bilateral music’. The studies that described auditory alternating stimulation also tended to use different terms. The most common term used was ‘BLS’ however this term does not tell you whether the study looked at auditory, tactile, visual or a combination of BLS. As a result of this I drew up a list for myself in order to try to unpack what each study was looking at. This was the list I used.
Terminology list for beat stimulation studies
Term | Full name | Description |
ABS | Auditory Beat Stimulation | This category incorporates both Binaural Beats (BBS) and Monaural Beat Stimulation (MBS) in research studies therefore I used this as a way of categorising both beat types. |
BLS | Bilateral Stimulation | This term incorporates not only auditory but also tactile and visual bilateral stimulation. It is the term that is used in EMDR Therapy studies for all stimulation types. |
AABLS | Auditory Alternating Bilateral Stimulation | This applies to audio tones, sounds or music. |
SABLS | Somatosensory Alternating Bilateral Stimulation | For mixed sensory alternating bilateral stimulation, for example a buzzer in each palm that is tactile but also makes a noise |
TABLS | Tactile Alternating Bilateral Stimulation | For touch/tapping related stimulation |
VABLS | Visual Alternating Bilateral Stimulation | This refers to eye movements or light bars |
The ‘A’ in each of these terms refers to ‘alternating’ and this is what sets this type of stimulation apart from other beat stimulation studies such as binaural beats. The alternating aspect has been found to be important in processing mood states and also in activating the vestibular feedback mechanisms in the brain (Nieuwenhuis et al., 2013; Boukezzi et al., 2017; Rousseau et al., 2020).
Conclusions
From the available data, it can be said that AABLS can influence the reduction of fear, especially when remembering a fearful event. There is also some evidence to suggest that AABLS can have this effect on the emotion of disgust as well.
Does this type of music have an impact on attentional focus or other aspect of functioning?
There was no data to support the role of AABLS on attentional focus. There was however data to support the use of binaural beats, at 40Hz for attentional focus.
There were no studies that used the term ‘bilateral music stimulation’ in their title. The closest in term and in concept is auditory bilateral stimulation, or BLS. This term was originally used in EMDR therapy to describe alternating stimulation. It is now starting to be used in other areas, such as in studies of virtual reality. BLS involves either eye movements, tapping, or a single tone presented to the left and right ears in a rhythmic alternating pattern. Auditory BLS has been researched as part of EMDR trauma studies and has been shown to be helpful in reducing fear-based memories ((Boukezzi et al., 2017). It is a single-tone and not a composed piece of multipart music.
There is a therapy that has evolved from EMDR therapy which does use bilateral music, (not just a single tone), to help clients process traumatic memories. This therapy is called ‘Brainspotting therapy’ ((Grand, 2013). Initial studies have shown that it can be as effective as EMDR therapy. A point of difference between the two therapies is that EMDR uses a single alternating bilateral tone, whereas Brainspotting uses music that has melodic, harmonic, and rhythmic content, with an alternating bilateral pulse within the music. However, there is no research evidence linking this to mood state yet.
Another type of music that has been researched for its effects on well-being is ‘Binaural beat’ music, also known as ‘Auditory beat stimulation’. This music has been subjected to several large-scale studies, as well as a systematic review and meta-analysis, and has been shown to have effects on anxiety, pain perception and attentional focus (Chaieb et al., 2015; Garcia-Argibay, Santed-Germán and Reales, 2019). It has evolved from a single tone to now being bespoke music composed with a binaural pulse built in.
Binaural music differs from Bilateral music in that it presents a slightly different frequency to each ear. It is this difference between the left and right ear, like crosstalk from a set of speakers, that is said to produce a therapeutic effect. However, it is not yet known whether the effect is due to frequency differences, communication between the left and right hemispheres of the brain, or rhythmical entrainment (Christman and Propper, 2010).
It is possible that bilateral music and binaural music share similar processes, however, there are no studies to date that have compared the two. There is no single definition of bilateral audio or explanation of its features. There is also the question of whether a single alternating bilateral tone can produce the same effect as a piece of composed music.
Both types of music can be said to be examples of ‘Functional Music’, that is, music for a specific purpose, rather than just to listen to music for its own sake. Functional music as a term appears to be becoming a category of music. A search on the website AHrefs (https://ahrefs.com), using the term ‘functional music’, ‘UK’ and ‘Worldwide’, indicates the popularity of this term has risen sharply since 2020.
The studies that were discovered in this review indicate that single tone, alternating auditory bilateral stimulation is being used in EMDR Therapy studies to have an impact on traumatic memories, specifically to reduce negative mood states and the salience of the traumatic memory. The type of tone is usually not described in much detail but is said to be a single tone, rather than multipart music. However, in Brainspotting therapies the music is of a multipart type and the playlists on various social media and streaming platforms are multipart pieces of music. The research literature however does not currently support the effects of these multipart pieces of bilateral stimulation music. It is possible that multipart music could have significant effects. Certainly, in studies of entrainment it has been found that by adding instruments and varying the introduction of these instruments this leads to an increase in perceived groove and sensorimotor coupling. By varying the instruments this helps to maintain attention which means a person is more likely to focus on what is happening in the present rather than becoming carried away by a negative emotion.
Terminology
Perhaps the term ‘AABLS’ should be used to distinguish alternating auditory beats from non-alternating monaural or binaural beats. The term AABLS also separates auditory alternating bilateral stimulation from other types of bilateral stimulation used in EMDR therapy, such as tactile or visual.
Future research could tease apart the differences between single tone and multipart bilateral sound, and the differences between monaural and binaural beats and bilateral sound, especially in relation to mood states. It would also be useful to note if this type of sound could enhance a positive mood state, such as the emotion of awe.
Playlist suggestions for bilateral music
These playlists were selected on 29th August 2023 from Spotify.
I collected ten playlists from Spotify. The attached screenshot shows the raw data. The tempo range was 93-120, with the mean being 116.2 BPM. The most common mood was ‘acoustic, obscure and relaxing’. The most common key was C Major, and the average length of tracks was 5 minutes and 15 Secs.
The mean length of the tracks across all 10 playlists was 5 mins and 15 secs. The average BPM was 116.2 and the most popular key was ‘C’ however there was large variation in key with some tracks being F#, Gb or D.
I have created my own track based on the above information. The track I created is called ‘The Spiral Waltz’.
Title: The Spiral Waltz: Bilateral Music
BPM: 112
Key: D# Minor
Length: 5 mins 22 Secs
Time: 3 / 4
You can listen to this track here.
References
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