MINI REVIEW ARTICLE
published: 18 April 2012
Meditation and its regulatory role on sleep
Ravindra P. Nagendra, Nirmala Maruthai and Bindu M. Kutty*
Department of Neurophysiology, National Institute of Mental Health and Neurosciences, Bangalore, India
V. Mohan Kumar, Sree ChitraTirunal
Institute for Medical Sciences and
Sunao Uchida, Waseda University,
V. Mohan Kumar, Sree ChitraTirunal
Institute for Medical Sciences and
Bindu M. Kutty, Department of
Neurophysiology, National Institute of
Mental Health and Neurosciences,
Bangalore 560029, India.
Intense meditation practices help to achieve a harmony between body and mind. Medi-
tation practices inﬂuence brain functions, induce various intrinsic neural plasticity events,
modulate autonomic, metabolic, endocrine, and immune functions and thus mediate global
regulatory changes in various behavioral states including sleep. This brief review focuses
on the effect of meditation as a self regulatory phenomenon on sleep.
Keywords: meditation, sleep, brain functions, autonomic activity, endocrine functions, neural plasticity
Meditation practices have been a life style practiced in India thou-
sands of years ago. Proﬁcient meditative practices help to integrate
the brain functions, regulate various physiological mechanisms
resulting in a state of mental and physical well being. Studies
of long term transcendental meditation (TM) practitioners have
shown that TM helped to achieve a state of “restful alertness” a
state of deep physiological rest which was associated with periods
of respiratory suspension without compensatory hyper ventilation,
decreased heart rate, heightened galvanic skin response along with
enhanced wakefulness (Wallace, 1970). This restful alertness and
hypometabolic state were believed to be the outcome of physi-
ological and biochemical changes brought about by meditation
practices (Young and Taylor, 1998).
MEDITATION, BRAIN FUNCTIONS, AND SLEEP
The effect of meditation on sleep was ﬁrst reported by Mason et al.
(1997) in practitioners of TM. The main objective was to evaluate
the neurophysiological correlates of the higher states of conscious-
ness during sleep. The study reported that the senior meditators
spent more time in the slow wave sleep (SWS) with higher theta–
alpha power with background delta activity,together with reduced
electromyogram (EMG). The rapid eye movement (REM) sleep
was also found to be enhanced. The distinct theta–alpha pattern
observed during sleep was considered as an electrophysiological
correlate of a stabilized state of higher consciousness in sleep. Fur-
ther, the study opened up new avenues to explore the inﬂuence of
meditation on sleep.
Studies by Sulekha et al. (2006) and Ravindra et al. (2010)
demonstrated the differences in sleep architecture in practi-
tioners of Vipassana meditation (mindfulness meditation). The
sleep architecture of senior practitioners of Vipassana medita-
tion was endowed with enhanced states of SWS and REM sleep
compared to that of non-meditating control group. Vipassana
meditators showed 17.95, 11.3, and 10.63% of SWS among
younger (30–39 years), middle (40–49 years), and older (50–
60 years) age groups respectively. On the other hand, the corre-
sponding non-meditating controls showed a signiﬁcant reduction
of SWS with increasing age, i.e., 11.29, 6.65, and 3.94%. Vipas-
sana meditators from all age groups showed more number of
sleep cycles, indicating quality sleep. The study suggested that
the older meditators could retain the sleep pattern of younger
non-meditating controls. Aging is known to reduce the activity of
the slow wave resonating mechanism either by actual loss of neu-
rons or reduced activation of thalamo-cortical pathways (Feinberg
et al., 1967;Mourtazaev et al., 1995) and also by reduced spin-
dle generation during NREM sleep stage 2 (Nicolas et al., 2001).
Vipassana meditation appears to preserve the SWS,suggesting that
meditation could prevent the age associated changes in the slow
wave generating mechanisms.Vipassana meditation also enhanced
the REM sleep states. Meditation practices are reported to enhance
the amplitude of gamma synchrony, strengthen the thalamo-
cortical and cortico-cortical interactions (Lutz et al., 2004). These
mechanisms brought about stronger network synchronization and
altered the neural structure and functions (Lazar et al., 2005;
Pagnoni and Cekic, 2007). Based on the above observations, the
changes in sleep architecture in the Vipassana meditation practi-
tioners could be attributed to the neural plasticity events associated
MEDITATION, AUTONOMIC ACTIVITY, AND SLEEP
Changes in autonomic activity had been reported with respect
to speciﬁc sleep states with predominant parasympathetic activ-
ity in SWS and sympathetic activity during REM sleep (Pivik
et al., 1996;Otzenberger et al., 1997;Trinder et al., 2001;Pede-
monte et al., 2005). Such sleep state dependent autonomic changes
maintain the homeostasis during sleep. Aging alters autonomic
ﬂexibility leading to an overall increase in sympathetic activity
along with reduced parasympathetic activity, thereby bringing
about autonomic arousal and decrease in sleep quality. Reduced
www.frontiersin.org April 2012 | Volume 3 | Article 54 | 1
Nagendra et al. Meditation and sleep
parasympathetic activity along with inefﬁcient baroreﬂex mecha-
nisms during REM sleep have been reported to cause unfavorable
cardiac events (Somers et al., 1993;Ramaekers et al., 1999;Jones
et al., 2003). Meditation practices help to bring about sympatho-
vagal balance with parasympathetic predominance among experi-
enced meditators and also in novice meditators with less practice
(Wu and Lo, 2008;Zeidan et al., 2010). Vipassana meditation prac-
tices help to retain the ﬂexibility of autonomic activity during
different stages of sleep. Further, heart rate variability evalua-
tion during REM sleep showed higher sympathetic activity in
meditators than in controls. This higher sympathetic activity in
meditators was effectively buffered by parasympathetic activity
unlike the non-meditating controls (unpublished data). These
studies have demonstrated a greater insight into the modula-
tory effect of meditation practices on autonomic functions during
sleep. Meditation practices are associated with enhanced frontal
midline theta activity (Aftanas and Golocheikine, 2001;Travis and
Shear, 2010). The frontal midline theta activity originates from the
anterior cingulate cortex and controls the parasympathetic activ-
ity (Tang et al., 2009). Vipassana meditation practices would have
activated the anterior cingulate cortex and hence modulated the
parasympathetic activity during sleep. These reports are sugges-
tive of a positive modulatory role of meditation in sleep through
MEDITATION, MELATONIN, AND SLEEP
Meditation practices were reported to regulate the hypothalamo
pituitary adrenal (HPA) Axis and thereby the cortisol and cat-
echolamine levels (Jevning et al., 1978a;Infante et al., 2001).
Further,meditation techniques were also known to increase dehy-
droepiandrosterone (Glaser et al., 1992), anterior Pituitary hor-
mones like growth hormone, thyroid stimulating hormone (TSH),
prolactin (Jevning et al., 1978b;Werner et al.,1986;MacLean et al.,
1997), and melatonin levels (Massion et al., 1995;Tooley et al.,
Melatonin plays a vital role in the physiological regulation of
sleep in both blind and normal individuals (Pandi-Perumal et al.,
2006). Melatonin rhythm follows a raising and falling phase with
corresponding alterations in sleep propensity (Dijk and Cajochen,
1997;Dijk et al., 1997). Melatonin exerts its hypnotic effect by
acute inhibition of suprachiasmatic nucleus (von Gall et al., 2002)
and also by facilitating hypothermic response through peripheral
vasodilatation (Krauchi et al., 1997). Melatonin is widely used in
the management of sleep rhythm disorders due to jetlag, shift-
work, and insomnia (Martinez and Lenz, 2010). In addition to its
role in sleep, melatonin acts as an antioxidant and immunomod-
ulator (Maestroni, 2001), oncostatic, antiaging agent, and helps in
bringing sense of wellbeing (Armstrong and Redman, 1991;Reiter,
1995;Maestroni, 2001;Guerrero and Reiter, 2002;Pandi-Perumal
et al., 2006). Aging attenuates the melatonin secretion (Sack et al.,
1986) and hence affect the sleep quality in aged population.
Meditation practices are reported to enhance the melatonin
levels (Tooley et al., 2000), the precursors of melatonin espe-
cially the serotonin (Bujatti and Riederer, 1976) and noradren-
alin (Lang et al., 1979). Meditation increases melatonin concen-
tration by slowing its hepatic metabolism or augmenting the
synthesis in the pineal gland (Massion et al., 1995). Diurnal
melatonin levels were found to be signiﬁcantly high in Vipassana
meditators (approximately 300pg ml) than non-meditating con-
trols (65 pg ml; unpublished data). By considering the role of mela-
tonin in sleep maintenance, it might be concluded that meditation
practices enhance melatonin levels and hence quality of sleep.
SLEEP AS AN AUTOREGULATORY, GLOBAL PHENOMENON
Sleep is reported to be associated with reduced heart rate, blood
pressure, respiratory rate, and rhythm, oxygen consumption, anx-
iety or arousal, and an overall decrease in basal metabolic levels
leading to a hypometabolic state. This phenomenon of sleep
induced hypometabolic state is a natural and spontaneous out-
come necessary for biological survival (Young and Taylor, 1998).
Imaging studies have shown that during NREM sleep the blood
ﬂow to areas associated with executive functions such as frontal
and parietal cortex, thalamus, basal ganglia, and cerebellum has
been reduced and bringing about the feeling of hypnogogic effect
during sleep (Kajimura et al., 1999;Kjaer et al., 2002).
Meditation also brings a sustained hypometabolic state termed
as relaxation response by Herbert Benson and helps in sleep initia-
tion (Wallace et al., 1971). Similarly,meditation techniques help to
regulate the blood ﬂow to the executive regions of the brain dur-
ing sleep (Lou et al., 1999). Meditation practices down regulate
HPA axis reducing the stress, prolactin, TSH levels (Jevning et al.,
1978a); bring about alterations in the intermediary metabolism
favoring an anabolic state. Thus, meditation helps to maintain a
wakeful hypometabolic state with parasympathetic predominance
(Young and Taylor, 1998). Both the state and trait characteristics of
meditation practices provide an advantage that it continually resets
the metabolic functioning despite varying levels of stress. This
internal metabolic resetting form the baseline trait characteristics
necessary for all potential changes brought about by meditation
practices. Further, meditative practices beneﬁcially inﬂuence the
cognitive, emotional, and behavioral aspects. Thus meditation is
shown to have a greater potential to inﬂuence many physiological
and behavioral states including sleep (Carlson et al., 2007;Ong
et al., 2008;Sibinga et al., 2011).
It has been hypothesized that meditation practices activate
prefrontal cortex, fronto-limbic, fronto-parietal neural networks
and limbic and paralimbic cortices associated with sympathetic
arousal. Meditation practices activate structures like insula, ante-
rior cingulate, and hypothalamus and bring about autonomic and
humoral changes (Newberg and Iversen, 2003). Meditation thus
produces a continuum of global regulatory changes at various
behavioral levels favoring quality sleep.
It is evident from the literature cited that practice of medita-
tion brings about global changes. Many of these alterations in
physiological functions have great similarities to the changes that
are happening during sleep. It has been proposed that sleep is
an autoregulatory global phenomenon (Kumar, 2010). It is also
true that meditation inﬂuences sleep and its functions. It appears
that various components of sleep generating mechanisms can be
altered with meditation. Meditation, with its global effects on body
and brain functions helps to establish a body and mind harmony.
Thus meditation practices as an autoregulatory integrated global
phenomenon, opens a wider scope for understanding the unique
aspects of human sleep and consciousness.
Frontiers in Neurology | Sleep and Chronobiology April 2012 | Volume 3 | Article 54 | 2
Nagendra et al. Meditation and sleep
Aftanas, L. I., and Golocheikine, S. A.
(2001). Human anterior and frontal
midline theta and lower alpha reﬂect
emotionally positive state and inter-
nalized attention: high-resolution
EEG investigation of meditation.
Neurosci. Lett. 310, 57–60.
Armstrong, S. M., and Redman, J.
R. (1991). Melatonin: a chronobi-
otic with anti-aging properties? Med.
Hypotheses 34, 300–309.
Bujatti, M., and Riederer, P. (1976).
Serotonin, noradrenaline, dopamine
metabolites in transcendental
meditation-technique. J. Neural
Transm. 39, 257–267.
Carlson, L. E., Speca, M., Faris, P.,
and Patel, K. D. (2007). One year
pre-post intervention follow-up of
psychological, immune, endocrine
and blood pressure outcomes of
mindfulness-based stress reduction
(MBSR) in breast and prostate
cancer outpatients. Brain Behav.
Immun. 21, 1038–1049.
Dijk, D. J., and Cajochen, C. (1997).
Melatonin and the circadian regu-
lation of sleep initiation, consolida-
tion, structure, and the sleep EEG. J.
Biol. Rhythms 12, 627–635.
Dijk, D. J., Shanahan, T. L., Duffy,
J. F., Ronda, J. M., and Czeisler,
C. A. (1997). Variation of elec-
troencephalographic activity during
non-rapid eye movement and rapid
eye movement sleep with phase
of circadian melatonin rhythm in
humans. J. Physiol. (Lond.) 505(Pt
Feinberg, I., Koresko, R. L., and Heller,
N. (1967). EEG sleep patterns as a
function of normal and pathologi-
cal aging in man. J. Psychiatr. Res. 5,
Glaser, J. L., Brind, J. L., Vogelman, J.
H., Eisner, M. J., Dillbeck, M. C.,
Wallace, R. K.,Chopr a,D., and Oren-
treich, N. (1992). Elevated serum
dehydroepiandrosterone sulfate lev-
els in practitioners of the transcen-
dental meditation (TM) and TM-
Sidhi programs. J. Behav. Med. 15,
Guerrero, J. M., and Reiter, R. J. (2002).
Melatonin-immune system relation-
ships. Curr. Top. Med. Chem. 2,
Infante, J. R., Torres-Avisbal, M., Pinel,
P., Vallejo, J. A., Peran, F., Gonza-
lez, F., Contreras, P., Pacheco, C.,
Roldan, A., and Latre, J. M. (2001).
Catecholamine levels in practition-
ers of the transcendental medita-
tion technique. Physiol. Behav. 72,
Jevning, R., Wilson, A. F., and Smith,
W. R. (1978a). The transcendental
meditation technique, adrenocorti-
cal activity, and implications for
stress. Experientia 34, 618–619.
Jevning, R., Wilson, A. F., and Vander-
Laan, E. F. (1978b). Plasma prolactin
and growth hormone during medi-
tation. Psychosom. Med. 40,329–333.
Jones, P. P., Christou, D. D., Jordan,
J., and Seals, D. R. (2003). Barore-
ﬂex buffering is reduced with age
in healthy men. Circulation 107,
Kajimura, N., Uchiyama,M., Takayama,
Y., Uchida, S., Uema, T., Kato, M.,
Sekimoto, M., Watanabe, T., Naka-
jima, T., Horikoshi, S., Ogawa, K.,
Nishikawa, M., Hiroki, M., Kudo, Y.,
Matsuda, H., Okawa, M., and Taka-
hashi, K. (1999). Activity of mid-
brain reticular formation and neo-
cortex during the progression of
human non-rapid eye movement
sleep. J. Neurosci. 19, 10065–10073.
Kjaer, T. W., Law, I., Wiltschiotz, G.,
Paulson, O. B., and Madsen, P. L.
(2002). Regional cerebral blood ﬂow
during light sleep – a H(2)(15)O-
PET study. J. Sleep Res. 11, 201–207.
Krauchi, K., Cajochen, C., Danilenko,K.
V., and Wirz-Justice, A. (1997). The
hypothermic effect of late evening
melatonin does not block the phase
delay induced by concurrent bright
light in human subjects. Neurosci.
Lett. 232, 57–61.
Kumar, V. M. (2010). Sleep is neither a
passive nor an active phenomenon.
Sleep Biol. Rhythms 8, 163–169.
Lang, R., Dehof, K., Meurer, K. A., and
Kaufmann, W. (1979). Sympathetic
activity and transcendental medita-
tion. J. Neural Transm. 44, 117–135.
Lazar, S. W., Kerr, C. E., Wasserman, R.
H., Gray, J. R., Greve, D. N., Tread-
way, M. T., McGarvey, M., Quinn, B.
T.,Dusek, J. A., Benson, H., Rauch, S.
L., Moore,C. I., and Fischl, B. (2005).
Meditation experience is associated
with increased cortical thickness.
Neuroreport 16, 1893–1897.
Lou, H. C., Kjaer, T. W., Friberg, L.,
Wildschiodtz, G., Holm, S., and
Nowak, M. (1999).A 15O-H2O PET
study of meditation and the resting
state of normal consciousness. Hum.
Brain Mapp. 7, 98–105.
Lutz, A., Greischar, L. L., Rawlings,
N. B., Ricard, M., and Davidson,
R. J. (2004). Long-term meditators
self-induce high-amplitude gamma
synchrony during mental practice.
Proc. Natl. Acad. Sci. U.S.A. 101,
MacLean, C. R., Walton, K. G., Wen-
neberg, S. R., Levitsky, D. K., Man-
darino, J. P., Waziri, R., Hillis, S. L.,
and Schneider, R. H. (1997). Effects
of the transcendental meditation
program on adaptive mechanisms:
changes in hormone levels and
responses to stress after 4 months
of practice. Psychoneuroendocrinol-
ogy 22, 277–295.
Maestroni, G. J. (2001). The
of melatonin. Expert Opin. Investig.
Drugs 10, 467–476.
Martinez, D., and Lenz, M. C. (2010).
Circadian rhythm sleep disorders.
Indian J. Med. Res. 131, 141–149.
Mason, L. I., Alexander, C. N., Travis,
F. T., Marsh, G., Orme-Johnson, D.
W., Gackenbach, J., Mason, D. C.,
Rainforth, M., and Walton, K. G.
(1997). Electrophysiological corre-
lates of higher states of conscious-
ness during sleep in long-term prac-
titioners of the transcendental med-
itation program. Sleep 20, 102–110.
Massion, A. O., Teas, J., Hebert, J. R.,
Wertheimer, M. D., and Kabat-Zinn,
J. (1995). Meditation,melatonin and
breast/prostate cancer: hypothesis
and preliminary data. Med. Hypothe-
ses 44, 39–46.
Mourtazaev, M. S., Kemp, B., Zwinder-
man, A. H., and Kamphuisen, H. A.
(1995). Age and gender affect differ-
ent characteristics of slow waves in
the sleep EEG. Sleep 18, 557–564.
Newberg, A. B., and Iversen, J. (2003).
The neural basis of the complex
mental task of meditation: neuro-
transmitter and neurochemical con-
siderations. Med. Hypotheses 61,
Nicolas, A., Petit, D., Rompre, S., and
Montplaisir, J. (2001). Sleep spin-
dle characteristics in healthy sub-
jects of different age groups. Clin
Neurophysiol 112, 521–527.
Ong, J. C., Shapiro, S. L., and Manber,
R. (2008). Combining mindfulness
meditation with cognitive-behavior
therapy for insomnia: a treatment-
development study. Behav. Ther. 39,
Otzenberger,H., Simon, C., Gronﬁer,C.,
and Brandenberger, G. (1997). Tem-
poral relationship between dynamic
heart rate variability and electroen-
cephalographic activity during sleep
in man. Neurosci. Lett. 229, 173–176.
Pagnoni, G., and Cekic, M. (2007).
Age effects on gray matter vol-
ume and attentional performance in
Zen meditation. Neurobiol.Aging 28,
Pandi-Perumal, S. R., Srinivasan, V.,
Maestroni, G. J., Cardinali, D. P.,
Poeggeler, B., and Hardeland, R.
(2006). Melatonin: nature’s most
versatile biological signal? FEBS J.
Pedemonte, M., Rodriguez-Alvez, A.,
and Velluti, R. A. (2005). Electroen-
cephalographic frequencies associ-
ated with heart changes in RR inter-
val variability during paradoxical
sleep. Auton. Neurosci. 123, 82–86.
Pivik, R. T.,Busby, K. A., Gill, E., Hunter,
P., and Nevins, R. (1996). Heart rate
variations during sleep in preadoles-
cents. Sleep 19, 117–135.
Ramaekers, D., Ector, H., and Aubert,
A. E. (1999). The inﬂuence of age
and gender on heart rate variabil-
ity (HRV). J. Am. Coll. Cardiol. 33,
Ravindra, P. N., Sulekha, S.,
Sathyaprabha, T. N., Pradhan,
N., Raju, T. R., and Kutty, B. M.
(2010). Practitioners of vipassana
meditation exhibit enhanced slow
wave sleep and REM sleep states
across different age groups. Sleep
Biol. Rhythms 8, 34–41.
Reiter, R. J. (1995). Oxygen radi-
cal detoxiﬁcation processes during
aging: the functional importance
of melatonin. Aging (Milano) 7,
Sack, R. L., Lewy, A. J., Erb, D. L.,
Vollmer, W. M., and Singer, C. M.
(1986). Human melatonin produc-
tion decreases with age. J. Pineal Res.
Sibinga, E. M., Kerrigan, D.,Stewart, M.,
Johnson, K., Magyari, T.,and Ellen, J.
M. (2011). Mindfulness-based stress
reduction for urban youth. J. Altern.
Complement. Med. 17, 213–218.
Somers, V. K., Dyken, M. E., Mark,
A. L., and Abboud, F. M. (1993).
Sympathetic-nerve activity during
sleep in normal subjects. N. Engl. J.
Med. 328, 303–307.
Sulekha, S., Thennarasu, K.,
Vedamurthachar, A., Raju, T.
R., and Kutty, B. M. (2006). Eval-
uation of sleep architecture in
practitioners of Sudarshan Kriya
yoga and Vipassana meditation.
Sleep Biol. Rhythms 4, 207–214.
Tang, Y. Y., Ma, Y., Fan, Y., Feng, H.,
Wang, J., Feng, S., Lu, Q., Hu, B.,
Lin, Y., Li, J., Zhang, Y., Wang, Y.,
Zhou, L., and Fan, M. (2009). Cen-
tral and autonomic nervous system
interaction is altered by short-term
meditation. Proc. Natl. Acad. Sci.
U.S.A. 106, 8865–8870.
Tooley, G. A., Armstrong, S. M., Nor-
man, T. R., and Sali, A. (2000). Acute
increases in night-time plasma mela-
tonin levels following a period of
meditation. Biol. Psychol. 53, 69–78.
Travis, F., and Shear, J. (2010). Focused
attention, open monitoring and
automatic self-transcending: cat-
egories to organize meditations
from Vedic, Buddhist and Chi-
nese traditions. Conscious. Cogn. 19,
www.frontiersin.org April 2012 | Volume 3 | Article 54 | 3
Nagendra et al. Meditation and sleep
Trinder, J., Kleiman, J., Carrington, M.,
Smith, S., Breen, S., Tan, N., and
Kim, Y. (2001). Autonomic activity
during human sleep as a function of
time and sleep stage. J. Sleep Res. 10,
von Gall, C., Stehle, J. H., and Weaver,
D. R. (2002). Mammalian melatonin
receptors: molecular biology and
signal transduction. Cell Tissue Res.
Wallace, R. K. (1970). Physiological
effects of transcendental meditation.
Rev. Bras. Med. 27, 397–401.
Wallace, R. K., Benson, H., and
Wilson, A. F. (1971). A wake-
ful hypometabolic physiologic
state. Am. J. Physiol. 221,
Werner, O. R., Wallace, R. K., Charles,
B., Janssen, G., Stryker, T., and
Chalmers, R. A. (1986). Long-
term endocrinologic changes in
subjects practicing the transcen-
dental meditation and TM-Sidhi
program. Psychosom. Med. 48,
Wu, S. D., and Lo,P. C. (2008). Inward-
attention meditation increases
parasympathetic activity: a study
based on heart rate variability.
Biomed. Res. 29, 245–250.
Young, J. D., and Taylor,E. (1998). Med-
itation as a voluntary hypometabolic
state of biological estivation. News
Physiol. Sci. 13, 149–153.
Zeidan, F., Johnson, S. K., Gordon, N.
S., and Goolkasian, P. (2010). Effects
of brief and sham mindfulness med-
itation on mood and cardiovascu-
lar variables. J. Altern. Complement.
Med. 16, 867–873.
Conﬂict of Interest Statement: The
authors declare that the research was
conducted in the absence of any com-
mercial or ﬁnancial relationships that
could be construed as a potential
conﬂict of interest.
Received: 21 March 2012; paper pending
published: 26 March 2012; accepted: 27
March 2012; published online: 18 April
Citation: Nagendra RP, Maruthai N and
Kutty BM (2012) Meditation and its reg-
ulatory role on sleep. Front. Neur. 3:54.
This article was submitted to Frontiers in
Sleep and Chronobiology, a specialty of
Frontiers in Neurology.
Copyright © 2012 Nagendra, Maruthai
and Kutty. This is an open-access article
distributed under the terms of the Cre-
ative Commons Attribution Non Com-
mercial License, which permits non-
commercial use, distribution, and repro-
duction in other forums, provided the
original authors and source are credited.
Frontiers in Neurology | Sleep and Chronobiology April 2012 | Volume 3 | Article 54 | 4