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Brain Wave Entrainment by Binaural Beats & Music in Recovery of Coma

by Joshi, Jitesh Narendra, MS

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1.1 Description of the work


Music can be a powerful stimulus to affect states of the brain. In this project, the
therapeutic effect of music was to be investigated for recovery in comatose patients.
Also the effect of binaural beat brain wave entrainment was to be studied in context of
activation of brain in disorders of consciousness.




Literature review on coma, entrainment and music.

Design, implement and analyze experiments

1.1.1 Problem Statement

There have been very few attempts to apply non-invasive methodologies for aiding the
recovery from coma. Music as a method to activate and rehabilitate cognitive functions
of brain needs to be quantitatively studied for its effectiveness in recovery in disorders of
consciousness. Observations of clinical music therapists and information gathered from
recovered coma-patients indicate the strong influence of music in the recovery. Earlier
research studies on binaural beats have shown frequency following responses and have
argued induction of rhythmic neural-activity in healthy human brain [1, 2]. Though,
utmost care has to be taken while proposing new methodologies of treatment for
comatose patients owing to their critical state.
Previous research shows that the neural response to sensory overload activates
the habituation response which lowers awareness by decreasing vigilance [3]. Rather
than a continuous bombardment of multisensory stimulation, researchers and clinicians
suggest meaningful stimuli under carefully controlled conditions, with the reduction of
all forms of extraneous noise. Recent experiments with cognitive evoked potential have
also shown the validity of applying meaningful musical stimulus [4]. This thesis is an
attempt to review previous research about music therapy in motor and cognitive
rehabilitation for comatose patients, study the literature on music in neuro-rehabilitation
and design and analyze experiments to study the neuronal effect of binaural entrainment
using EEG measurements.


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2.1 Disorders of Consciousness

2.1.1 Arousal & Awareness

In order to understand the loss of functions suffered by a comatose individual,
important characteristics of the conscious state have to be understood. Consciousness is
defined by two fundamental elements: awareness and arousal [5].

Arousal is regulated solely by physiological functioning. Its primitive
responsiveness to the world is demonstrated by predictable reflex (involuntary)
responses to stimuli. Arousal is maintained by the reticular activating system (RAS).
This is not an anatomical area of the brain but rather a network of structures (including
the brainstem, the medulla, and the thalamus) and nerve pathways which function
together to produce and maintain arousal.

Awareness is a more complex process as it involves cognitive processing or
thought [6]. Awareness allows us to receive and process information communicated by
the five senses and thereby relate to ourselves and the rest of the world. Awareness is
regulated by the cortex as a part of a feedback loop between the cortex, sub-cortical
nuclei and the various perceptual systems. Abnormalities or trauma that interrupts the
neuro-transmission process can lead to coma or various states of impaired awareness
along the continuum of consciousness.

2.1.2 Major Breakthrough

The seat of consciousness till recent past was widely believed to be in the heart,
and the absence of heartbeat was regarded as the clinical sign of death. Neuroscientific
evidence has superseded such thinking and has shown that consciousness, an emergent
property of neural activity, resides in the brain [7]. Since the invention of the positivepressure
mechanical respirator, it has become possible to sustain cardiorespiratory
function in individuals who are in a coma, so that research can focus on brain function
as a separate entity.

Patients who would previously have died from apnea are now able to survive in
profound comatose states that had never been encountered before. This technological
progress forced modern medicine to redefine the diagnosis of death and move from its
ancient cardiorespiratory-centered definition to a neurocentric one, where death is
defined as the irreversible loss of all brainstem reflexes (including the breathing reflex).
Since the introduction of this clinical definition, not a single patient who fulfils the
criteria of brain death has ever regained consciousness [8].


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2.2 Coma

Coma is characterized by the absence of arousal and thus also of consciousness.
It is a state of un-arousable unresponsiveness in which the patient lies with the eyes
closed and has no awareness of self and surroundings. Although there are gradations in
the depth of coma, the patient lacks the arousal cycles of sleep-wakefulness
characteristic of vegetative state. The behavioural repertoire of coma consists entirely of
reflex activity and indicates failure of both the reticular activating system and the cortex
[5]. Comatose patients who survive begin to awaken and recover gradually within 2 to 4
weeks or enter a vegetative or minimally conscious state. There have been few standard
behavioural measures to diagnose the severity of coma, as Glasgow Coma Scale, Coma
Recovery Scale. One of the recently emerged EEG based objective measures is Bispectral
Index, which is under investigation by leading researchers and not widely used
Early stimulation of cortical neuronal networks is thought to maintain arousal
and improve long-term cognitive outcomes after brain injury as patients in coma
experience sensory deprivation [9]. Muti-modal sensory stimulation and uni-modal
stimulation with auditory stimulation have been experimented by early researches. The
study designs using multimodal stimulation have shown better results than those using
unimodal stimulation and have more unequivocal results [10]. As hearing is the last
faculty to deteriorate before death, auditory stimulation is very promising in comatose
patients. Following mentioned states of coma based on its severity provides basis for
envisaging auditory or music stimulus as aiding tool in the recovery.

2.2.1 Vegetative State
Patients in a vegetative state are awake but unaware of self and environment
[11]. They usually show reflex or spontaneous eye opening and breathing. At times they
seem to be awake with their eyes open, sometimes showing spontaneous roving eye
movements and occasionally moving trunk or limbs in meaningless ways; at other times
their eyes are shut and they appear to be asleep. They may be aroused by painful or
prominent stimuli opening their eyes if they are closed, quickening their breathing,
increasing heart rate and blood pressure and occasionally grimacing or moving.
Pupillary, corneal, oculocephalic and gag reflexes are often preserved. They can make a
range of spontaneous movements including chewing, teeth-grinding and swallowing.
More distressingly, they can show rage, cry, grunt, moan, scream or smile reactions
spontaneously or to non-verbal sounds. Their head and eyes sometimes, inconsistently,
turn fleetingly towards new sounds or sights.

The functional preservation of the brainstem maintains arousal and autonomic
functions in these patients. In studies of patients in VS, simple noxious somato-sensory
[12] and auditory [13, 14] stimuli have shown systematic activation of primary sensory
cortices and lack of activation in higher order associative cortices from which they were
functionally disconnected [15].

2.2.2 Minimally Conscious State
"Minimally conscious state" replaces the term "minimally responsive state"
which was first defined by the American Congress of Rehabilitation Medicine in 1995.
It is used to describe patients who are unable to follow instructions reliably or


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communicate, but who demonstrate inconsistent but reproducible behavioural evidence
of awareness of the environment or self-awareness (American Congress of
Rehabilitation Medicine (1995). Patients in minimally conscious state can show
reproducible visual fixation and emotional or motor behavior that are contingent upon
the presence of specific eliciting stimuli such as episodes of crying that are precipitated
by family voices only, command following, object manipulation, intelligible
verbalization and gestural or verbal yes/no responses.

The medial parietal cortex (precuneus) and adjacent posterior cingulate cortex
seem to be brain regions that differentiate patients in MCS from those in VS [16].
Interestingly, these areas are among the most active brain regions in conscious waking
and are among the least active regions in altered states of consciousness such as general
anesthesia, sleep, hypnotic state, dementia, and postanoxic amnesia [15].

2.2.3 Locked-In Syndrome

Classically, structural brain imaging (magnetic resonance imaging) may show
isolated lesions (bilateral infarction, hemorrhage, or tumor) of the ventral portion of the
basis pontis or midbrain. It is important to stress that EEG and evoked potentials do not
reliably distinguish the locked-in syndrome from the vegetative state. These findings
emphasize the terrifying situation of an intact awareness of self and environment in
sensitive beings, locked in immobile bodies [17]. Locked-In Syndrome may easily be
mistaken for VS, because of the lack of physical response to the environment present in
both conditions.

However, unlike the person in VS, the person in a locked-in state is able to
indicate awareness. Locked-in syndrome is a rare condition where patients are aware of
what is happening around them but are physically unable to respond to the environment
due to the impact that injuries have had on motor functioning including vocal
expression. Often vertical eye movements or eye blinking can be establishes as a form
of communication with other. Patients in a locked-in state have both physical and high
emotional needs. Cognitive skills such as insight and awareness of their impairments
may be relatively intact, which can lead to significant emotional adjustment issues in the
recovery process.

In sensory stimulation and regulation treatment, it is preferable for patients to be
exposed to a minimal amount of appropriate stimulation to reduce sensory overload and
to be given time with no sensory input so that they are able to rest. Consistency and use
of keywords in treatment are important [15, 18]. It is interesting to note that there is no
evidence to determine whether enjoyable stimulus or unpleasant stimulus is more
effective and it is under research in music therapy [15].

2.3 Therapeutic Interventions

The effectiveness of sensory stimulation programs for coma arousal is currently
under debate in the medical literature [3].The controversial issues concern measures of
outcome, such as the distinction between awareness and arousal. These programs are
based on the notion that increased volume or intensity of stimulation is more likely to


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force the patient to respond, however such stimulation procedures are used to test reflex
responses rather than to encourage voluntary behavior. Further on these grounds,
attempt has been made as per U.S. Pat. No. 5,611,350 for treatment of deep coma of a
patient by surgically attaching an electrode to a cranial nerve and stimulating patient‟s
brain by electrical pulse train generated as per on-going brain waves (neuro-feedback)
and other physiological measures. The present thesis work is to investigate effectiveness
of non-invasive binaural beat stimulation in recovery of coma.

2.3.1 Binaural Beat Entrainment

Binaural beats were discovered in 1839 by a German experimenter, H. W. Dove.
The human ability to "hear" binaural beats appears to be the result of evolutionary
adaptation. Many evolved species can detect binaural beats because of their brain
structure. The frequencies at which binaural beats can be detected change depending
upon the size of the species' cranium. In the human, binaural beats can be detected when
carrier tones are below approximately 1000 Hz (Oster, 1973). Below I000 Hz the wave length
of the signal is longer than the diameter of the human skull. Thus, signals below 1000 Hz curve
around the skull by diffraction

The audio phenomenon known as binaural beating can be used to access altered
states of consciousness [19]. This is done through a process in which individuals in an
environment of restricted stimulation willfully focus attention on a combination of
multiplexed audio binaural beats that are mixed with music, pink sound, and/or assorted
natural sounds. The binaural-beat element of the process appears to be associated with
an electroencephalographic (EEG) frequency-following response in the brain. Many
studies have demonstrated the presence of a frequency-following response to auditory stimuli,
recorded at the vertex of the human brain (top of the head) [1]. This EEG activity was termed
"frequency-following response" because its period (cycles per second) corresponds to the
fundamental frequency of the stimulus. Stated plainly, if the audio stimulus is 40 Hz the
resulting measured EEG will show a 40 Hz frequency following response using appropriate
time-domain averaging protocols. Binaural beat stimulation, coupled with the effects of the
other procedures within the process outlined above, appears to regulate neuronal activity and
encourage access to propitious mental states. The effectiveness of binaural beats in engendering
state changes is supported by the consistent reports of thousands of users, as well as the
documentation of physiological changes associated with its use [19].

Figure 1: 10Hz Binaural Beats


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2.3.2 Physiological Phenomenon of Binaural Entrainment
Perceived as a fluctuating rhythm at the frequency of the difference between the
two (stereo left and right) auditory inputs, binaural beats appear to originate in the brain
stem's superior olivary nucleus, the site of contra-lateral integration of auditory input
[20]. This auditory sensation is neurologically routed to the reticular formation and
simultaneously volume conducted to the cortex where it can be objectively measured as
a frequency-following response. The frequency-following response provides proof that
the sensation of binaural beating has neurological efficacy. Binaural beats can easily
be heard at the low frequencies (< 30 Hz) that are characteristic of the EEG spectrum.
This perceptual phenomenon of binaural beating and the objective measurement of the
frequency-following response suggest conditions which facilitate alteration of brain
waves and states of consciousness [20].

Figure 2: Physiological mechanism for the perception of Binaural Beats

Binaural beats in the delta (1 to 4 Hz) and theta (4 to 8 Hz) ranges have been
associated with reports of relaxed, meditative, and creative states, sensory integration,
and used as an aid to falling asleep. Binaural beats in the alpha frequencies (8 to 12 Hz)
have increased alpha brain waves and binaural beats in the beta frequencies (typically
16 to 24 Hz) have been associated with reports of increased concentration or alertness,
improved memory, and increases in focused attention in mentally retarded adults.
Passively listening to binaural beats may not automatically engender an altered state of
consciousness. The process usually used when listening to binaural beats includes a
number of procedures; binaural beats are only one element [1, 20, 21].


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We all maintain a psycho-physiological momentum, a homeostasis which may
resist the influence of the binaural beats. These homeostatic states are generally
controlled by life situations as well as by acts of will, both conscious and subconscious.
The willingness and ability of the listener to relax and focus attention or their level of
practice in meditative processes may in some way contribute to binaural-beat
effectiveness. Naturally occurring neurological ultradian rhythms, characterized by
periodic changes in arousal and states of consciousness, may underlie the anecdotal
reports of fluctuations in the effectiveness of binaural beats. The perception of a
binaural beat is said to be heightened by the addition of masking noise to the carrier
signal [20], so white or pink noise is often used as background. Practices such as
humming, toning, breathing exercises, autogenic training, and/or biofeedback can also
be used to interrupt the homeostasis of subjects resistant to the effects of binaural beats.

2.3.3 Hemispherical Synchronization

Many of the states of consciousness attainable through the technology of
binaural beats have been identified and they result in hemi-spherically synchronized
brain-wave frequencies [20]. Although synchronized brain waves have long been
associated with meditative and hypnagogic states, the binaural-beat process may be
unique in its ability to induce and improve such states of consciousness. The reason for
this is physiological. Each ear is "hardwired" to both hemispheres of the brain. Each
hemisphere has its own olivary nucleus (sound-processing centre) which receives
signals from each ear. In keeping with this physiological structure, when a binaural beat
is perceived there are actually two electrochemical synaptic waves of equal amplitude
and frequency present, one in each hemisphere. This is, in and of itself, hemispheric
synchrony of synaptic activity. Binaural beats appear to contribute to the hemispheric
synchronization evidenced in meditative and hypnagogic states of consciousness.
Binaural beats may also enhance brain function by enabling the user to mediate crosscolossal
connectivity at designated brain-wave frequencies [20].

2.3.4 Habituation

Nonetheless, when it comes to brain activation and stimulation in disorders of
consciousness, in VS, MCS and LS states, we need to keep in mind that there are very
few functional connections in their brain and as long as complete effect of phenomena is
not understood in these states, application of binaural beats can be not recommended.
As the neuro-scientific studies argue the possible phenomenon of habituation that might
occur while patients are exposed to binaural beats and this might result in low vigilance
in lieu of being useful in brain activation [3]. Previous studies show that on a long span
of time, repeated use of entrainment stimulus may suppress the cooperation between the
hemispheres [22]. First reaction on listening to binaural beats by all participants in the
experiment for thesis has been very similar to this understanding of habituation, as there
is nothing exciting about listening to the same sound for long duration.


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2.4 Music as a Therapy

2.4.1 Background
Throughout human history, music has been considered a form of
communication. However, the nature of what and how music communicates has been
the subject of long-standing and fascinating inquiries in philosophy, religion, the arts
and the sciences. Considering the non referential embodied meaning as a core function
in musical communication, an understanding of the major organizing syntactical
elements in music is of utmost importance. One of the most important characteristics of
music is its strictly temporal character. Music unfolds only in time and the physical
basis of music is based on time patterns of physical vibrations transduced in our hearing
apparatus into electrochemical information that passes through the neural relays of the
auditory system to reach the brain. Within this temporal basis two core dimensions
emerge: sequentiality and simultaneity [24]. Music‟s particular nature permits it to
express both at once. Language is sequential but monophonic. Rhythm can access and
powerfully influence some core elements of the perceptual mechanisms that drive
patterns of meaning in symbolic communication of artworks.

First, discernible temporal distribution and organization of events in groupings
imposed by a rhythmic structure allow for better perceptual gestalts to emerge,
minimizing conflict and difficulty in perception. Both Gestalt psychology of perception
and perceptual neuroscience emphasize innate drive to search for pattern structures that
allow the emergence of larger units of events, a way of imposing order and meaning
onto the perceptual process. Second, rhythm as temporal ordering process especially
in its narrower sense as cyclical, periodic phenomenon - creates anticipation and
predictability. Prediction and anticipation are key terms in certain theories of emotion
and meaning that have been extrapolated to the theories of emotion and meaning in
music. Temporary violations of expectations or predictions as in compositional
structures in music have potential and opportunity for arousal increments that are related
to the search for meaningful resolutions in the process of violating expectations [24].
These arousals from musical pieces can accelerate recovery of coma under proper
supervision and needs thorough investigations in further researches.

2.4.2 Neuroplasticity & Recovery
Recently, neuroscience has been able to demonstrate that the brain is not
structurally static but capable of self-modification and considerable reorganization
following neurological trauma [24, 25]. In the same way that new pathways and
waterways are formed after a geological catastrophe such as a flood or an earthquake,
new neural pathways can develop in the brain after a neurological trauma. This
reorganization enables patients to relearn skills despite a loss of function in areas of the
brain [24]. This process has been termed as 'neuroplasticity'.

Kolb (2004) explains that the process of neuroplasticity occurs at the synaptic
level, particularly the changes in the structure and number of glia cells. He states that
when neurons lose synapses during neurological trauma, there is retraction of dendritic
arborisation. Here, the branch-like structure of dendrite end of the neuron retracts and
increases the dendritic space within the synapse, reducing the potential for a successful
neurotransmission. Conversely, when neurons gain synapses, there is an extension of
dendritic arborisation.


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To facilitate a good functional outcome, rehabilitation techniques should be
employed that facilitate dendritic growth so as to increase the neurotransmission of
information within the brain and from the brain to the rest of the body. As the popular
notion of neuro-science says "Use It or Lose It" and "The neurons which fire together,
wire together", so the cells stimulated to fire in synchrony (of music) strengthen the
neurotransmission between two neurons, where as non-synchronous firings (in any
non synchronous sensory stimulation) inhibits connectivity and will increase the
synaptic space reducing the potential for successful neuro-transmission later. Kolb
(2004) asserts that changes within individual cells are the basis of plasticity in the brain.
In fact, this is the basis for all learning and the basis for neuro-reorganization.

This brief description of neuroplasticity above offers foundations to the ways in
which to approach for music therapy in comatose patients. Research suggests that rich
and different experiences are necessary to create multiple connections between neurons.
So, rather than encourage repetitive practice of the same skill in the same way, therapy
should aim to progressively develop increasingly difficult skills in novel ways [24]. In
doing so, connections are more likely to develop and strengthen neuro-activity. Further
the researches say that intrinsic organization occurs in local circuits in regions directly
or indirectly disrupted by injury [25], these often being adjacent to the damaged area.
So, for example, when Broca's area is damaged resulting in Broca's aphasia, the
undamaged areas of the brain immediately adjacent to Broca's area may begin to take
over the lost function. This is only possible in partial damage to Broca's area as in
complete damage a full recovery is unlikely.

Research has shown that the complementary areas in the opposite cerebral
hemisphere are able to adopt the responsibility of the lost function [25]. So again in the
case of impairment of expressive speech functions caused by damage to Broca's area
(left hemisphere), the area in the right hemisphere directly opposite Broca's area has
been shown to 'light' up in the brain scans when neurologically impaired patients
attempt to verbalize.

While neuroplasticity explains cortical reorganization and positive outcomes
from rehabilitation [24], it is unlikely that a localized structure like the adult cerebral
cortex could undergo a whole-scale reorganization of cortical connectivity when severe
brain damage occurs [25]. However, some research in the neuroscience field suggests
that this type of reorganization may be possible in the developing paediatric brain.

2.5. Hypothesis

Having reviewed basic literature in the context of coma, recovery, music
therapy, entrainment and brain waves & EEG, quite optimistic remark can be made
about the potential of entrainment and music therapy in recovery of coma and further
higher cognitive & functional rehabilitation. Considering the scope of this thesis, only
one little step can be made in this direction as every steps need serious study before
going towards pragmatic recovery program for coma with music therapy.


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As here the idea is of non-invasive approach with auditory entrainment towards
recovery of coma, binaural beats are chosen as simplistic auditory stimulus to be
analysed in this thesis work. Binaural beats fall in between sensory stimulation and
invasive electric brain stimulation. It has potential because of the physiological
phenomenon happening at brain stem, which tries to stimulate the nervous system and
establishes hemispherical synchronization. With pilot experiments to check for the
entrainment effect, the original idea was to develop neuro-feedback loop to control the
parameters of entrainment as per the need by monitoring physiological signals of
subject. Though tools were developed for neuro-feedback, but due to no proper
entrainment effects observed in many pilot experiments, this development could not be

Original hypothesis: Binaural beat stimulation can activate brain in comatose
patients and can enhance recovery by controlled auditory stimulation.

Experimented hypothesis: Binaural beats can entrain brain waves at the stimulus
frequency and can establish hemispherical synchronization in healthy subjects.


To study the effects of brain wave entrainment as per understanding of
physiological phenomenon happening under binaural beat stimulation, proper
operational measures needs to be monitored using EEG. With review of earlier
researches, two most relevant measures which emerge in this context are: 1) Mean Band
Power at specific EEG bands and 2) Mean Phase coherence at specific EEG bands.
Mean Band Power measures the gross effect of entrainment at specific EEG
bands by the comparison of band power before stimulus, on stimulus and after stimulus
conditions. This measure has been used by earlier researches as the basis to claim
frequency following response of binaural beats brain wave entrainment.
Mean Phase Coherence is relatively new measure and accounts for synchronized
activity of brain. It has recently been used as a measure to observe the functional
connectivity of brain [27]. In the present context of binaural beat brain wave
entrainment, phase synchronization of EEG from independent neuronal sources is to be

3.1 Binaural Beats Generation

Binaral Beat with pink noise from Gnaural ( with
following specification was presented as stimulus:
1) Binaural Beat:
Event Duration: 180 seconds
Beat Frequency: 7Hz, 14Hz, 21Hz
Base Frequency: 220Hz
Volume Right (range 0 - 1.0): 0.8
Volume Left (range 0 - 1.0): 0.8
2) Pink Noise:
Event Duration: 180 seconds
Volume Right (range 0 - 1.0): 0.2
Volume Left (range 0 - 1.0): 0.2


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