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Abstract
The term yoga-nidra has been used in many empirical studies
to refer to relaxation and guided imagery. These techniques do
not represent the intention or physiological correlates of yoga-
nidra discussed in the traditional yoga literature. We propose
an operational definition of yoga-nidra that is supported by
several physiologically testable hypotheses regarding its out-
comes and effects. Traditional descriptions of yoga-nidra and
contemporary accounts of its practice are reviewed, and studies
examining the physiological correlates of yoga-nidra are exam-
ined. Proposed hypotheses for future research using this opera-
tional definition are provided.
Key Words: yoga-nidra, mindfulness, neurophysiology,
yoga literature
Corresponding author: parkpsych@yahoo.com
Yoga-nidra is a pop
ular subject for seminars about yoga practice
and yoga therapy. Although many teachers use the term yoga-
nidra as a syn onym for relaxation (Feuerstein, 1999), some
practices have little relationship to the traditional definitions in
the literature. In the majority of studies of yoga-nidra, subjec-
tive questionnaires and rating scales were used to examine the
effects of relaxation protocols; however, yoga-nidra’s physiolog-
ical and neurological processes were not systematically evaluat-
ed. Consequently, the operational definition of yoga-nidra has
become diluted and confused, making systematic hypothesis
testing and cross-study comparison and replication difficult.
We propose an operational definition of yoga-nidra that is
based on the traditional yoga litera
ture and accounts for empir-
ically measurable, physiological markers th at distinguish it
from other states of relaxation. Physiological studies, particu-
larly those measuring brain function using electroencephalog-
raphy (EEG) and positron emission tomography (PET) may
support Swami Rama of the Himalayas’s assertion that “all of
the body is in the mind but all of the mind is not in the body”
(Rama, 2002, p.58).
A Proposed Definition
In 2011, Sw a mi Veda Bhar a ti sponsored an inte rnati onal con f e r-
e n ce on yoga-nidra to revi ew tr a d iti onal desc ripti ons and me t h-
ods of pr a cti c e, ev aluate cu rre n t re search, and promote a dia-
l o g u e . The goal was to initiate a discuss i o n be tween tho se re pre-
se n
ti n g the or al tr a d iti o n of yoga and re sea rch sc i e n tists. Bhar ati,
a former profe s sor of South As ian studies at the Un i ve rs i ty of
Mi n n e sota, is among the mo st se n i or monks in Ind ia’s Sw am i
ord e r. He has inhe rited the histori cal and or al - i n itiatory tr a d i -
ti on of the great ph il o sophe r, Sank ar a carya, th rou gh initiati on
from his guru, Sw a mi Rama of the Hi malay as. Bhar ati propo sed
a defi n iti o n of four levels of yoga-nidra pr a c tice that would pro-
vide measu r able phy s i o l o gi cal hy pothe ses for empi ri cal inve s ti-
g a ti on. Spec i fi cally, yoga-nidra (yoga sl eep) re p re se nts a state in
wh i ch an ind ivi dual demonstr ates all the symptoms of dee p,
non-REM sl ee p, inclu d i ng delta br a in waves, w
h ile simultane-
ously re mai n i n g fully consc i ous.
Neurologic Activity
Delta waves (frequency of ≤ 4 hz) are most consistent with deep
non-REM sleep. Theta waves (4–8 hz) are associated with con-
centration and meditation, dreams, hypnosis, and hypnogogic
imagery. Alpha waves (8–13 hz) indicate deep physical relax-
ation, and beta waves (> 13–30 hz) suggest alert functioning of
the waking state. Gamma waves (30–80 hz) indicate processing
involving multiple sensory modalities and execution of specific
cognitive or motor functions. For a detailed review of medita-
tion studies that used EEG, refer to Cahn & Polich, 2006.
T he te rm yo g a - nidra is often used to re fer to proc e sse s
and pr a c tices that are pre par atory to yoga-nidra prope r. We
s
u gge st a defi n iti o n that includes four disti nct levels of pr a c-
ti c e. Level 1 re pre s e nts a state of deep rela x ati on. Du r i ng th is
phase the br ain fi rst produces alpha waves, wh i ch may ve rge
on the ta waves du ri ng dee p er pr a cti c e. The s e dee p er exe rc ise s
may be used for sel f - h eal i ng, su c h as redu c i ng bl o od pre ssu re
and deal i ng with migr ai ne hea d a ches, among othe rs. The s e
protoc o ls are similar to tho s e used in cl i n i c al hy pno s i s
( Ham mond, 1990).
Level 2 represents a state that is characterized by creativity,
invention, achieving decisions and solutions to problems, and
c o mpo s i ng lectu res and re s earch pa
pe rs, poe t ry, minutely
detailed action plans, and the like. This stage is evidenced by
theta waves that verge on delta waves during deeper practice.
During Level 3, the practices of Level 1 result in the transi-
tion to yoga-nidra, or the state of abhava-pratyaya; that is, cog-
nition of negation in a cave of the heart center (Yoga Sutras I.10;
see Bharati, 1986; Zambito, 1992). During this state, the brain
may initially produce theta waves, followed by delta waves. The
participant experiences deep non-REM sleep but remains aware
of his or her surroundings. Attainment of this level may require
i n stru c ti o n by an adv anc ed tea che r. Sw ami Rama of the
Himalayas recommended that one not remain in Level 3 in
excess of 10 minutes at a single time.
Progression to Level 4 occurs after the first three lev
els are
mastered. During Level 4 the mind simultaneously remains in
International Journal of Yoga Therapy — No. 23 (1) | 2013 11
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Defining Yoga-Nidra: Traditional Accounts, Physiological Research,
and Future Directions
Stephen Parker, PsyD, E-RYT 500,
1,2
Swami Veda Bharati, DLitt,
3,4,5
Manuel Fernandez, PhD
6
1. St. Mary's University, 2. University of St. Thomas, 3. Himalayan Institute Hospital Trust University of Medical Sciences,
4. Swami Rama Sadhaka Gram, 5. Sadhanamandir Ashram, 6. Center Mahamudra
ARTICLE
two sta tes consisting of sleep and simultaneous conscious
awareness (a-japa japa, or the effortless repetition of a mantra
in spontaneous meditation) and meditation during which the
person is aware of kundalini. Kundalini is the subjective experi-
ence of the very subtle power of consciousness in meditation. A
practitioner may alternate between theta and delta waves dur-
ing this process. Unlike Level 3, which is time limited, this
process may last as long as 3.5 hours.
When Levels 3 and 4 are mastered, one may gradually tran-
sition into turiya, during which yoga-nidra and turiya become
indistinguishable. Turiya is a state during which the highest
form of meditation in samadhi (called asamprajñata [a-cogni-
tive] in yoga and nirvikalpa [free of t
ho ught] in Vedanta)
becomes one’s normal state of awareness and is maintained at
all t imes (see definitions from Yoga-vasistha, translated in
Venkatesananda, 1993). It is hypothesized that at this point,
EEG readings may register no discernible electrical activity.
This hypothesis has yet to be demonstrated under controlled
conditions.
Traditional Yoga Literature
Descriptions of yoga-nidra in the traditional yoga text tend to
be oblique and often refer to the state of yoga-nidra rather than
descriptions of the practice. When discussing the traditional
yoga text we are not rigidly referring to texts of formal yoga phi-
losophy. Because yoga is primarily a discipline of meditation,
we have taken into consideration information about meditation
practices from multiple oral and written p
erspectives, including
the yoga Upanishads and Vedantic, Ayurvedic, and Buddhist
texts. Though the topic of yoga-nidra is vast, there is a paucity
of descriptions related to relaxation exercises and subtle-body
practices. For example, the hatha yoga texts contain few explic-
it descriptions of yoga-nidra, which might lead one to conclude
that few exist (see Vasistha-samhita III.57-75; Yoga Yajnavalkya
VII-1-37, translated in Bharati, 2001; 771–773).
The Oral Tradition of Yoga
There are two potential explanations for the scarcity of textual
accounts of yoga-nidra. First, many practices were traditionally
taught in response to the ne eds of the individual and were
almost solely communicated by word of mouth (Bharati, 2001).
Second, the injunction, “Do not teach! Do not teach! Do
not
teach!” was very common in texts about yoga practice (prayoga-
sastra). As such, written descriptions are often partial a nd
devoid of essential details. Further, the practices of yoga-nidra
were often reserved for those deemed to be qualified, which was
determined in the context of a one-to-one relationship between
teacher and student.
One of the pramanas (means of correct knowledge) in the
yoga system is agama, “that which has come,” usually translated
as scripture (Monier-Williams, 1899,1970; Zambito, 2010). The
yoga tradition includes the action and speech of a master as
agama, not what is solely written in the books (Bharati, 1986).
It is important to consider the oral teachings as well as the writ-
ten works, many of which were deliberately left incomplete or
did not explain the practice of yoga-nidra in its entirety.
Therefore, w
e do not rely exclusively on written material when
we refer to the textual tradition of yoga.
Vedic and Epic Literature
The term yoga-nidra can refer to practice as well as to an object
of devotion. In the Vedic literature (roughly 5000 BCE to 1000
CE) and Epic literature (approximately 700 BCE to 1000 CE),
yoga-nidra refers to the mythological dissolution of the cosmos,
or Vishnu’s cosmic yoga-nidra. It also r epresents Vishnu's
power of tamas, or the universal p rinciples of inertia and
entropy, and is identified with the Divine Mother as Kali, the
shakti of cosmic tamas (see Jagadishswarananda, 2003, for fur-
ther description). Yoga-nidra may also refer to a deity who was
involved in the birth of Krishna (Campbell, 1974).
Jainia and Buddhist Literature
The Mahayana Buddhist traditions, and the Vajrayana in par-
ticular, refer to a practice of clear, light sleep similar to classical
yoga’s account of yoga-nidra. This light sleep is described in the
fou r tee nth centu r y text, Book of Three In spiration s , by
Tsongkhapa the Great, guru of the first Dalai Lama (Mullin,
2005). This practice involves concentrating on the heart center,
the cakra, associated with the state of deep sleep. The individual
progresses through four stages of emptiness to an “experience of
a light like that of a dawn with a clear sky” (Mullin, 2005). Its
description is identical to that of the practices included in the
Yoga-Vedanta and Tantric traditions (Aiyar, 2000; Dyczkowski,
1998; Rama, 1982; Rama, 1988).
These experiences are described in Mahayana tradition as
states of samadhi. It is likely t
hat the clear, light state is very sim-
ilar to the state of turiya described by Vedantic writers from
Gaudapada onward. As with turiya, the clear, light state is an
experience beyond which there are “no further signs” (i.e., the
highest attainment, liberation), and it eventually pervades all
states of consc i o us n e s s, waki ng, dream i ng, and sl e e pi n g
(Mullin, 2005, p. 207). Through the experience of turiya, there
appears to be a practical link between the clear light meditation
practice and yoga-nidra.
The Theravada Buddhist yoga literature contains no refer-
ences to yoga-nidra, because it is described in the hatha-yoga
literature. The Tibetan Buddhist tradition has a discipline of
dream yoga, which does not apply to the state of deep sleep;
however, it is related to the practice of cle
ar, light sleep and
involves the dissolution of all thought and an experience of
nothing but pure awareness (Rinpoche, 1998). Although the
Jaina yoga literature includes some references to yoga-nidra, it
does not appear to include descriptions of yoga-nidra practice.
Ayurvedic Literature
In Ayurvedic literature, the Charaka-samhita, a revelation that
is partially ascribed to Patañjali, contains a discussion of the
theory of sleep in the Sutra-sthana, which culminates in the
verse, “The same sleep, if properly enjoyed, brings about happi-
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ness and longevity in human beings as the real kn owledge
brings about siddhi in a yogin” (Chandra & Dash, 2008, Verse
21.38). Although this intimates that sleep is an entry point to
elevated, superconscious states, no detailed description of the
practice is included.
Patañjali’s Yoga Sutras (approximately 200 BCE) does not
explicitly describe the technique of yoga-nidra, but the nature
of sleep as a mental operation is explored (I.10), as are the
dream and sleep states as a means to enter samadhi. Sutra I.10,
abhava - p rat yaya - alambana - v rt t ir- nidra, defi nes the me ntal
process (vrtti) of sleep as concentration on nescience (abhava)
and its cause (Bharati, 1986). This has important implications
for the practice of yoga-nidra. When used in
conjunction with
a mind that has no focus (alambana) or has nonbeing as a
focus, the mind becomes very malleable, and the power of the
mind field can be shaped by one’s intention (samkalpa). This is
valuable in processes of learning and self-healing. Even more
important is the observation of the dream (svapna) and deep
sleep (nidra) states as a means to enter into samadhi. Sutra I.38,
svapna-nidra-jñana-alambanam va, states that one may enter
samadhi “with su pport of knowledge of dream and [deep]
sleep” (Bharati, 1986, 361). The practical details of this process
are not described, however.
In Shiva - sutra I.7 of the Shaiva tr a d iti o n of Kash m i r
(approximately 950 CE), Vasugupta asserts that the yogi experi-
ences
the fourth state of consciousness (turiya) in the midst of
the other three states: waking, dream, and sleep. This gives rise
to a classification of states of consciousness wherein each of
these three states is inherent within the other (Shiva-sutra I.10).
The result is a schema of nine states of consciousness (10 or
more if you count turiya): waking in waking, waking in dream,
waking in deep sleep, dream in waking, dream in dreaming,
deep sleep in dreaming, and so forth (Dyczkowski, 1998; Jhoo,
2007; Singh, 1999). Several of these, particularly waking in deep
sleep (jagrat-susupti), dreaming in deep sleep (svapna-susupti),
deep sleep in dreaming (susupti-svapna), and deep sleep in deep
sleep (susupti-susupti), describe aspects of the levels of practice
of yoga-nidra mentioned by Bharati earlier in this
article. Verse
75 of the Vijñana-bhairava-tantra describes the nature of the
concentration on sleep through which this is accomplished:
When sl eep has not yet fully appeared, that is when one is
about to fall asl eep and all the exte rnal objects (thou gh pre s-
e nt) have faded out of sight, then the state (be tween sl ee p
and waki ng) is one on wh i ch one should conc e ntr a te. In
that state the Supre m e God d e ss will reveal he rself (Si ngh ,
1999, p. 70–71).
Though most written references describe the state of yoga-
nidra as the goal, three texts describe the process of achieving
yoga-nidra in some detail. The Hathayogapradipika (IV.43–50)
describes the process of khecari-mudra, which culminates in the
attainment of yoga-nidra (Digambarji & Kokaje, 1998).
The
Shandilya-upanishad (I.35) describes a similar process with the
same sequence of steps (Aiyar, 2000). Finally, Shankaracarya
also describes the process of going into yoga-nidra in his Yoga-
taravali (Deshikachar & Deshikachar, 2003).
In Hathayogapradipika and Shandilya-upanishad (IV. 43-
44), the process of entry into yoga-nidra is described in similar
terms. When the sushumna-nadi or shunya-svara, the central of
the three primary energy channels of the energy body (prana-
maya - k osa), “seizes the prana, khecari is establ i shed”
(Digambarji & Kokaje, 1998, p. 147). From establishment of
khecari, the state of unmani, the “upw ard mind,” ensu e s
(Digambarji & Kokaje, 1998, p. 148.) “One should practice khe-
cari until yoga-nid
ra is attained. Once yoga-nidra is attained,
there is no such thing as kala (time)” (Digambarji & Kokaje;
1998, p. 149). The text proceeds to describe the state as one in
which there is no thought, and life activities (vayu, movement
of prana) are reduced to a minimum.
In Ve r ses 17–26 of the Yo g a - tara vali, Shank a r a c ary a
describes entry into th e state of yoga-nidra. Verses 17–19
describe movement into the state of unmani, a state in which
the mind and senses are under volitional control and inhalation
and exhalati o n cease (kevala - kumbhaka; De s h i k a c har &
Deshikachar, 2003). Verses 21 and 22 relate how yogis enter
amanasaka-mudra, a s tate in which there is no activity of
manas, then describe how the breath transcends t
he mind (has
entered the sushumna-nadi) and how they “are linked to the lit-
tle space in their hearts” (Deshikachar & Deshikachar, 2003, pp.
56–57). In this state the mind (manas) is described as “void of
activity” (vritta-shunya). This state, sahaja, is “spontaneous” or
“natural,” and there is no activity of the senses (Deshikachar &
Deshikachar, 2003, pp. 58–59). The state of yoga-nidra then
occurs. Specifically, “when both intentions and imagination are
cut off, when uprooted from the web of karma, through unbro-
ken practice, the yogini achieves yoga-nidra” (Deshikachar &
Deshikachar, 2003, pp. 62–63). The practitioner is encouraged
to remain in turiya, in the nirvikalpa state. It is evident from
Shankaracarya’s explanation that activity of the sensory and dis-
putative mind (manas) ceases ent
irely in the state of yoga-nidra.
In the highest state of turiya, neither the s ensory nor other
aspects of mind evidence activity, though the person m ay
appear to be awake.
Contemporary Yoga Literature
T h e conte mpor a ry yoga lite r atu re includes a nu mber of
descriptions of methods of yoga-nidra. Miller’s (2005) general
description states that “during yoga-nidra, we enter into a state
that approximates sleep during which dream-like movements
spontaneously appear. But unlike sleep, during which the mind
identifies with these movements, during yoga-nidra we bear
witness to these mental dream-like fragments” (Miller, 2005, p.
34.) He goes on to describe a series of processes of dealing with
thoughts and images, memories a
nd visualizations, which he
pairs with levels of embodiment according to the Vedanta con-
ceptualization of five bodily sheaths or koshas. Finally, he reach-
es a point at which he prescribes making “the great turn” dur-
ing which “in Being, the ego-I, thought could not be sustained.
It dissolves into its source. . . . Observe how the mind stops and
thinking dissolves. . . . This is what happens in deep sleep”
(Miller, 2005, p. 55). In this last step, Miller may come closer
than anyone to achieving the traditional description of one’s
awareness in yoga-nidra.
Satyananda, of the Bihar School of Yoga, describes several
prel i m i n ary pr a ctices related to yoga-nidra. They include (a)
Yoga Nidra: An Examination of the Construct 13
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making mental resolution or setting an intention (samkalpa),
(b) initiating rotations of consciousness through the body, (c)
practicing breath awareness (nostrils, throat, chest, counting
the breath), (d) relaxing the mind and emotions, (e) visualizing
various images, and (f) reaffirming mental resolutions or inten-
ti o ns (samk a lpa; Sar a s w ati, Sw ami Saty a nanda, 1998).
Although this is the most detailed description of the prelimi-
nary practices of yoga-nidra, it does not include resting the
mind in the heart center or instruction about how to enter a
state of deep sleep during which the mind, as manas, does not
function. These methods are also not consistent with Shankara’s
definition.
Satyananda’s successor, Swami Niranjanananda Saraswati,
als
o briefly discusses yoga-nidra in his book, Yoga Darshana
( S ar as w ati, Sw ami Ni r anjanananda, 1993). In additi o n to
d e s c r ibi ng the proc e ss of yoga-nidra in similar te rms to
Satyananda, he denotes three preliminary levels of yoga-nidra.
No mention is made of the “mindless” state of yoga-nidra itself,
however.
Panda (2003) describes yoga-nidra vis-a-vis the eight limbs
of yoga. This description includes an array of asana and
pranayama techniques, as well as mudra and bandha practices.
Panda explains the Vedantic theory of the evolution of the
mind, the body she ath or kosha system, the cak ra system,
Kundalini, and a great deal of ancillary yoga-vedanta theory. In
his description of the preliminary practices of yoga-nidra, he
delineates several form
s of external and internal rotations of
consciousness, as well as a complex tantric system of nyasa
(Panda, 2003). He includes a discussion of Freudian psycho-
analysis and contrasts it with Indian theories of mind, then
briefly examines common threads between the two theories,
characterizing hypnosis as an externally suggested trance and
yoga-nidra as an “autosuggestion.” We contend that hypnosis is
a process of autosuggestion, whether or not it is accompanied
by external facilitation, and consider hypnosis to be a special
case of yoga-nidra. Last, Panda describes yoga-nidra as a state
between waking and dreaming, which is incorrect because it
misidentifies the brain waves emitted during yoga-nidra as pri-
marily theta rather than delta.
Swami Rama writes of five meth
ods of yoga-nidra and
describes two of them. The first is a full procedure that includes
preliminary relaxation exercises and a short method that fol-
l o ws maste r y of prel i m i nary rela x ati o n tech n i que s (Rama ,
1988). The full procedure begins with a mental statement of
intention to remain aware (samkalpa), followed by progressive
relaxation of major muscle groups. This is followed by a 61-
point relaxation that focuses on marma points, with the goal of
relaxing the subtle body, and “point-to-point breathing,” or
shithali-karana, t ranslated as “making or doing relaxation”
(Rama, 1988, p. 186–191). Shithali-karana entails cultivating
awareness of the flow of the breath from the crown of the head
through successive p
oints in the subtle body, exhaling and
inhaling, through the eyebrow, throat, and heart cakra f ive
times each. Awareness then moves to the heart center, with
nothing but awareness of the breath. An individual may use the
shorter method of breathing through the three upper cakras
five times each to quickly enter yoga-nidra in the heart center
after mastering the three preliminary relaxation practices.
The approaches that exclusively use r elaxation exercises
and visualizations do not lead to the absence of mental activity
described by Shankaracarya as essential to yoga-nidra. Rather,
they are relaxation techniques that are preliminary steps in the
process of yoga-nidra (for a detailed description of the practice,
see Rama, 1988).
Our review of the historical a
nd contemporary yoga text
suggests that yoga-nidra is a state during which activity of the
mind is suspended. Neither thoughts nor images are present,
and th e practitioner experiences conscious, deep, dreamless
sleep, possessing awareness of the surroundings but neither
thinking about them nor interacting with them. This review
suggests that methods of relaxation that exclusively use imagery
and/or relaxation are only preparatory steps in the process of
yoga-nidra. These activities produce predominantly alpha and
theta brain wave activity rather than the delta activity charac-
teristic of deep REM sleep.
Research Literature
The research literature about yoga-nidra is scarce and limited
by the lack of an empirical definition of the state of yoga-nidra.
A numb
er of investigations have examined various physiologi-
cal criteria related to yoga-nidra, but their lack of empirical
consistency and rigor make it difficult to draw any definitive
conclusions.
Early Physiological Studies
Early empirical studies of yoga-nidra were conducted in the
1970s and reported in several non-peer reviewed publications
(Greene & Greene, 1977; Moffat, 1974). In one investigation,
Swami Rama of the Himalayas participated in an EEG study of
yoga-nidra during which he was observed to enter conscious
deep sleep for about 10 minutes, at which time delta waves were
recorded. He was able to recount verbatim all the conversations
that occurred in the lab during that time, demonstrating his
awareness of his surroundings.
In his comments about this experiment, Swami Satyananda
sta
ted that “the capacity to remain consciously aware while pro-
ducing delta waves is one of the indications of the super con-
scious state, turiya” (Saraswati, Swami Satyananda,1998, pp.
176–177). Although it is true that someone in turiya would be
conscious of his/her surroundings, this kind of awareness is also
characteristic of t he state of yoga-nidra prior to entry into
turiya, according to Swami Rama an d Swami Veda Bharati.
Bharati contends that the state of turiya is accompanied by a flat
EEG rather than by delta waves, indicating a moment-to-
moment state of asa mprajñata or nirvikalpa-samadhi, when
measurable cognitive activity ceases altogether, despite appar-
ent wakefulness. To date, no carefully controlled demonstration
of such a state has been accomplished (Bharati,
2006).
In 2004 Dr. Dean Radin of the Institute of Noetic Sciences
used more tightly controlled experimental conditions in an
effort to replicate the Swami Rama study. A number of physio-
logical parameters were measured while Swami Veda Bharati
entered a state of delta wave sleep while maintaining conscious
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awareness of his surroundings, similar to Swami Rama’s experi-
ence (Bharati, 2006). After examining the EEG data collected
while talking with Swami Veda Bharati prior to the experiment,
Radin suggested that “Swami Veda's ordinary state of awareness
is analogous to that of a normal person in a deep meditative or
sleep state” (Bharati, 2006, p. 69). The EEG trace showed pre-
d o m i nant produ cti on of delta waves even du ri ng casual conve r-
sati on with his eyes open. Ne u r ol o gi cally, th is is highly unusual.
Recent Physiological Studies
Several empirical studies of the iRest method of relaxation
developed by Richard Miller have been conducted (Birdsall,
Pritchard, Elison-Bowers, & Spann, 2011; Engel et al., 2007;
Pritchard, Elison-Bowers, & Birdsall, 2010; S tankovic, 2011;
unpublished research at www.irest.u
s/programs/irest-research-
and-programs). These investigations used questionnaires and
rating scales to measure participants’ experience. They provid-
ed evidence of the subjective effectiveness of relaxation but did
not measure the physiological correlates associated with the
state of yoga-nidra. A discussion of their findings is beyond the
scope of this article.
In 1999, PET and EEG were used to assess changes in cere-
bral blood flow patterns in a sample of 9 yoga teachers, each
with more than 5 years of experience practicing relaxation
meditation (yoga-nidra). Researchers found consistent patterns
of brain activity during meditation and relaxation. Specifically,
EEG outcomes revealed alpha and theta waves during what was
described as the practice of yoga-nidra (Lou et al., 1999). These
patterns of
brain activity are consistent with those of states of
relaxation and meditation but do not meet the criteria for vol-
untary production of predominantly delta waves while retain-
ing conscious awareness. These findings represent evidence of
neurologic states attained during preliminary practices rather
than the state of yoga-nidra.
In another study, Kjaer and colleagues used PET scans to
examine dopamine production in the ventral striatum during a
yoga-nidra rela x ati o n med itati o n for 8 highly expe ri e n c e d
meditation teachers (Kjaer et al., 2002). They reported that
“subjectively, yoga nidra [was] characterized by reports of vivid
imagery and decreased attention towards action” (Kjaer et al.,
2002, p. 256). EEG data p
rovided evidence of increased theta
wave activity, which is consistent with an experience of imagery
(Kjaer et al., 2002). The traditional texts and the personal expe-
rience of Swami Veda Bharati maintain that neither imagery
nor other thought process are present during the state of yoga-
nidra, suggesting that participants were engaging in practices
that are preparatory to yoga-nidra.
Kumar and Joshi (2009) studied 40 students who were
tr ai ned in the yoga-nidra me t hod of Sw ami Saty a nanda
Saraswati (Saraswati, Swami Satyananda, 1998) and a specific
breath i ng exe r c i se (pranakarsa - p ranayama) devel oped by
Shriram Sharma Acharya. Students’ brain waves were measured
using EEG, and galvanic skin response was also assessed.
Participants’ beta wave activity was
gradually replaced by alpha
waves during the practice. Alpha waves indicate a state of relax-
ation preliminary to yoga-nidra, but not the predominant delta
wave pattern observed during the state of in yoga-nidra.
Another study examined EEG data for 20 individuals who
used the Bihar School of Yoga protocol for yoga-nidra. As in the
Kumar and Joshi study (2009), participants’ beta wave activity
was gradually replaced by alpha waves. After more than 30 ses-
sions of practice, alpha waves were found to be replaced by
some theta waves (Mandlik, Jain, & Jain, 2009). Because no
delta wave activity was detected, participants were likely in a
state of relaxation generation and imagery generation but not a
state of yoga-nidra. The production of theta waves suggests that
participants experienced the seco
nd level of practice prelimi-
nary to yoga-nidra.
T he se studies demonstr ate that what is often re fe rred to as
yo g a - nidra in conte mpor ary re search is often a state of dee p
rela x ati on and image ry ge ne r ati on that is a precu r sor to yo g a -
nidra. Du r i n g th i s state, alpha and the t a br ai nw a ves, as
oppo s ed to the delta wave activity fou nd du ri ng the state of
yoga-nidra, are re p orted. The state of yoga-nidra is devoid of
i mage r y, thou ght, and mantra re p e t iti on and cons i sts only of
the aw are ne ss of be i ng. This is char a c te ri z ed by aw a re ne ss of
the breath du r i ng wh i ch one ob se r ves the mind and body in
sl e e p. To date, extant re s earch and fi n d i n gs are inc ons iste nt
with
tho s e of early studies. It appears that yoga-nidra as it is
d e sc ribed by Shank ar a car ya and its phy s i ol o g i c al correlate s
have yet to be stu d i e d.
Implications for Empirical Investigation
Clearly, it is important to empirically test Shankaracarya’s tradi-
tional model of yoga-nidra, and as such, we suggest the follow-
ing hypotheses for empirical investigation:
1. The state of yoga-nidra represents a conscious entry into
a state of non-REM sleep. Individuals entering this state
will be observed to voluntarily generate predominantly
delta waves, as measured by EEG. Persons will also
demonstrate awareness of their surroundings, as
measured by the verbatim recall of a list of words.
2. Replication of existing yoga-nidra studies will reliably
demons
trate the production of alpha wave activity, a
precursor to entry into yoga-nidra proper.
3. Levels 2, 3, and 4 of Bharati’s model (clear predominance
of delta waves) will be empirically distinguished using
EEG data.
4. Consistent with Shankaracarya’s criterion, we predict
that the state of turiya will be indicated by an absence of
EEG-observed brain activity, which would indicate
cessation of mental activity (citta-vriti-nirodha). This has
yet to be demonstrated in carefully controlled conditions.
We suspect that the state of consciousness present in Level
2 of the Bharati model bears a strong resemblance to those
observed during clinical hypnosis. This has implications for a
wide range of lea
rning and self-healing strategies for both men-
tal and physical health. This line of inquiry will require further
refinement, particularly in terms of measurement of the EEG
correlates of hypnotic states. These hypotheses challenge the
contention that consciousness requires brain activity. While it
Yoga Nidra: An Examination of the Construct 15
www.IAYT.org
may appear ambitious, inquiry of this nature would test the
premise that yoga practices transcend the physical senses.
The studies involving Swami Rama of the Himalayas and
Swami Veda Bharati cited earlier provide preliminary support
for our hypotheses. A more carefully controlled pilot study is
under development at the Meditation Research Institute of
Swami Rama Sadhaka Grama in Rishikesh, India, in collabora-
tion with Dr. Shirley Telles. We hope to report study results sep-
arately in the future.
Postscript
Swami Rama once intentionally produced two cysts on his arm
while a group of German doctors watched. He identified one
cyst as malignant cancer and the other as benign. He asked that
biopsies be taken. He then made the two cysts di
sappear. The
biopsy results confirmed his prediction that one cyst was malig-
nant and the other benign (Greene & Greene, 1977). The physi-
cians did not publish their observations in fear of the reaction
of their coll eagues. Sw am i ji gave up su ch demonstr a ti ons
because it was clear that people would not believe what their
senses were telling them. Let us be rigorous in our empirical
study of yoga but courageous in accepting the challeng es of
what our rigor may reveal.
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