All night long: understanding the world of infant sleep.
Subject: Infants (Health aspects)
Growth (Case studies)
Sleep (Research)
Sleep disorders
Author: Porter, Lauren
Pub Date: 11/01/2007
Publication: Name: Breastfeeding Review Publisher: Australian Breastfeeding Association Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2007 Australian Breastfeeding Association ISSN: 0729-2759
Issue: Date: Nov, 2007 Source Volume: 15 Source Issue: 3
Topic: Event Code: 310 Science & research
Geographic: Geographic Scope: United States
Accession Number: 173187458

An understanding of the complex physiological, neurological and psychological world of the infant is important in order to provide recommendations about the sensitive and consistent care needed for optimal development. However, when it comes to the subject of infant sleep, professional and lay resources are often based on misinformation and scientific foundation for understanding infant sleep, this paper outlines normal infant sleep mechanisms, development and patterns as defined by the literature. Biopsychological data is also presented to demonstrate the study of infant stress, attachment and caregiving routines used to engage infants in sleep. this information can be used as a guideline for determining which sleep choices and approaches are healthy for infants and those which discourage optimal development and leave infants and families at risk.

Keywords: attachment, infant sleep, infant stress, neurology, sleep routines



Sleep is a basic requirement of human existence. Adequate sleep is required for good health and well-being. Yet sleep needs vary from person to person and change with age, stage and development. In infancy, sleep has distinct patterns and features that differ from adult sleep. 'Sleeping like a baby' does not mean long stretches of deep, uninterrupted sleep. Rather, it means shorter sleep cycles, significant amount of time in REM sleep, delayed establishment of a circadian rhythm (Anders & Taylor 1994) and a sleep mechanism that isn't fully formed until approximately between three (Sadeh & Anders 1993) and five years of age (Segawa 2006).

This paper presents a review of the literature on infant sleep, attachment and the neurological basis of night-time crying. It aims to provide a holistic and scientific foundation for understanding infant sleep.


While night waking in infancy can be considered problematic by parents who wish to get more uninterrupted rest, the majority of infants wake multiple times in the first months of life and require parental response (Anders, Halpern & Hua 1992). By eight months of age, somewhere between 60-70% of babies appear to be able to fall back asleep upon waking without parental assistance, and this process is known as 'self soothing' (Anders 1994). However, babies who do attain this ability to self soothe are not always able to achieve this at every waking. Conversely, even babies who typically 'signal' for a parent during the night are usually able to self soothe upon at least one of their night time wakings (Galyor, Goodlin-Jones & Anders 2001; Keener, Zeanah & Anders 1989). Additionally, night waking often increases at approximately one year of age, even for children previously sleeping for long periods 1985). This behaviour is thought to be due to developmentally appropriate responses to separation that are common to this age group (Anders & Eiben 1997). These observations highlight the indisputable fact that night waking is the norm for babies.

Night waking in infancy is not a bad thing since it appears to serve several protective, reparative and attachment functions, particularly from the point of view of survival, optimal development and emotional connection. For example, infants enter REM sleep first, have shorter sleep cycles and spend much greater amounts of time in light/REM sleep, and hence receive greater brain stimulation (Nakao 2006; Roffwarg, Muzio & Dement 1966), more access to breastmilk and maternal presence (McKenna et al 1997), and reduce their risk of SIDS by spending less time in deep sleep (Fleming et al 1996). For example, at 3 months of age, the average length of a sleep cycle is 50 minutes, whereas an average adult cycle is roughly 90 minutes (Middlemiss 2004). REM sleep also has important functions for emotional development. During REM sleep, emotional centres of the brain are highly activated, suggesting that REM sleep may be integral to the process of developing psychobiological attachment (McNamara, Dowdall & Auerbach 2002).


When evaluating and understanding infant sleep data and patterns, careful consideration must be given to the conditions, assumptions and criteria surrounding the research itself. McKenna (2001) discusses how much of the data in the sleep literature has been based on the paradigm of solitary-sleeping, artificially-fed infants. For example, when electrophysiological technology first became widely available to quantify infant sleep, breastfeeding initiation rates in the US were at 9%. Breastfeeding rates have improved since then, and we now know that the majority of babies sleep, at least sometimes, in the presence of a caregiver, yet the paradigm for what is 'normal' infant sleep was largely established during that foundational period. As a result, sleep 'problems' are often described as any patterns that deviate from this suboptimal standard. Hence, in order to create 'normal' and 'healthy' babies, as prescribed by a now-outdated standard, modern families are pressured to recreate the conditions prevalent when the research was conducted. Such conditions include feeding babies artificial baby milk, putting babies in isolated sleeping environments and extinguishing night waking.


As important as restorative, health-promoting sleep is to establishing well-being, bonding and attachment issues remain paramount in babies. Without bonding, babies fail to thrive (Fisher et al 1997) or even risk death (Spitz 1946). Attachment is a biological necessity that stems from the reliance of immature infants upon their caregivers for protection, advantage and basic survival (Bowlby 1982). The necessary protection is achieved via attachment relationships and consequently the degree to which we are excellent caregivers governs the degree to which our offspring reach optimal development (Perry 2001). Attachment security in infancy is associated with healthy mutually satisfying relationships, optimal cognitive functioning and emotional and behavioural management later in life (Karen 1994). Secure attachment relationships are marked by a mutual bond in which the mother, or other caregiver, shapes infant development through her interactions and relationship with her child (Bowlby 1982). These relationships then allow for the formation of an 'internal working model' that functions as a template by which babies can gauge their own emotions and those of others (Marvin & Britner 1999). The hallmarks of attachment security are availability, responsiveness and sensitivity (Ainsworth 1973). Hence it is not just the presence of the parent, but the quality of the parental response, their emotional availability and their sensitivity to the baby's communication that form the heart of a child's security (Kobak 1999). When a baby is cared for in this wholly sensitive way, a secure relationship will likely develop and form a foundation for emotional health that lasts a lifetime.

It is critical that infant sleep is approached with sensitivity to attachment needs and afforded high levels of attunement and responsiveness. All aspects of development are influenced by fundamental attachment relationships. For example, the human brain adds 70% of its structure after birth (Schore 2001). Hence our genetic potential is expressed via our experiences (Siegel & Hartzell 2004). Positive, nurturing parental response impacts the brain in two very important ways: it decreases the impact of subsequent stress on the brain (Cozolino 2006) and it enhances brain growth and the development of brain systems that support attachment, emotional regulation and problem solving (Davidson 2000). Babies who experience soothing touch, comforting warmth, repeated experiences of calming when distressed, a sustained positive emotional state and homeostatic balance when tired, hungry or overstimulated grow to develop healthy emotional regulation, brain growth and self esteem (Cozolino 2006). On the other hand, babies who experience neglect or abuse during their early life are at risk for mental illness, behavioural disturbances, cognitive impairment, and brain damage (McEwen 2000; Perry et al 1995). Because infancy is dedicated to an explosion in brain growth and neural connectivity, those years are widely considered the most critical period of development (Perry et al 1995). These are also the years that overlap with the most inconsistent sleeping patterns in babies.


Consistent with our cultural preferences for independent sleep, it is common for parents and professionals to have concerns about infant sleep patterns along with an accompanying desire to create longer, more stable night time sleep routines. The use of sleep techniques, such as controlled crying, is often recommended. These methods employ strategies in which a baby is left to cry for increasingly longer intervals until s/he learns to go to sleep independently. Depending on the authors, this strategy can be employed anywhere from birth through the first year of life (Ferber 1986; Hall 2006; Hogg & Blau 2002). However, sleep training overlooks a baby's psychological and physiological well being. Rather, it addresses a baby's behavioural repertoire and utilises interventions to affect change. When these approaches work--and their success is mixed and often unsustained (Middlemiss 2004)--they do so purely on a behavioural level and often at the expense of optimal emotional well-being (Gethin & Macgregor 2007). Similarly, approaches that emphasise independent, solitary sleep and discourage responsiveness to separation protests contradict our knowledge that mother-infant separation produces severe physiologic responses (Hofer, 2005).

Sleep training methods pose serious risks to infants. When babies are in close proximity to their mothers and when their needs are responded to with attuned sensitivity, babies remain regulated (Schore 2001). Babies are not born with an ability to independently regulate their physiological or emotional states but rely, instead, upon a caregiver to do this with and for them (Siegel 2001). We are all familiar with the need to place a newborn on their mother's chest to assist the baby with maintaining body temperature, due to the newborn's inability to regulate body temperature without assistance. Other aspects of regulation, such as heart rate, cortisol levels and digestion, are also regulated within the context of this relationship (Hofer 1996). These 'hidden regulators' are the physiological mechanisms that keep babies in homeostasis and form the foundation of future regulation (Hofer 1996).

Emotional regulation is the same. Babies need assistance in managing their emotions so they do not become overwhelmed. Whether its fear, sadness, surprise or excitement, babies can quickly succumb to emotional intensity. They are especially vulnerable to fear as they possess vast amounts of neural circuitry to analyse this emotion but few that assist them in feeling good (Cozolino 2006). Thus it is critical that babies be assisted in maintaining emotional balance and helped to return to a regulated state when out of balance. When they are dysregulated, babies are vulnerable to the deleterious effects of stress (Schore 2003).


Stress is the impact that our bodies experience when emotionally or physically challenged. The ability to handle stress is formed via our early experiences (Perry et al 1995). Subjection to repeated, frequent, ongoing or intense stressors leaves a baby prone to not only the negative effects of that experience but to a trajectory of future vulnerability to stressful events. For an infant, crying is typically the only way they have to communicate their stress. With adults, the 'fight or flight' response mobilizes our bodies to handle difficult or potentially overwhelming situations; for a baby, fight or flight only works if someone comes to fight for or flee with them (Perry 2001). Hence, leaving them to cry only increases their stress levels, teaches them they cannot rely on their caregivers for assistance, and opens them to the cycle of hyperarousal and dissociation that characterises the stress response.

When babies experience persistent or intense stress, they enter a cycle of hyperarousal and dissociation (Perry et al 1995). The initial stage of the stress cycle is one of hyperarousal, that is, the 'startle' reaction to a threat. This reaction engages the sympathetic nervous system, which increases the heart rate, blood pressure and respiration rate. Distress at this stage is usually expressed by crying, which will progress to screaming. The brain attempts to mediate this by increasing the levels of major stress hormones: adrenaline, noradrenaline, and dopamine. Elevated hormone levels trigger a hypermetabolic state in the developing brain (Brown 1982). This state can have negative consequences since the release of stress hormones is only a short term protective mechanism aimed at assisting the body in surviving a dangerous situation. Prolonged periods spent in this state are damaging. Additionally, prolonged exposure to stress induces increased levels of thyroid hormones and vasopressin (Schore 1994). Vasopressin, a hypothalamic neuropeptide, is released in response to unsafe or challenging environments (Schore 2002). It is also associated with nausea and vomiting, which may explain why many babies throw up after extended crying (Beebe 2000).

The second, later-forming reaction to stress is one of dissociation. At this point, the baby disengages from the external stimuli and retreats to an internal world. This second phase involves numbing, avoidance, compliance and lack of reaction (Schore 2002), and occurs in the face of a stressful situation in which the baby feels both hopeless and helpless (Schore 1994). The infant tries to repair the disequilibrium but cannot so s/he disengages, becomes inhibited, and strives to avoid attention in an effort to become 'unseen' (Schore 1994). This metabolic shutting-down is a passive state in response to an unbearable situation and is the opposite of hyperarousal. In biological terms, it is the same process that allows us to retreat from overwhelming situations in order to heal wounds and fill depleted resources. However, as a response to caregiver misattunement and non-responsiveness, it is devastating and the effects of even short periods of dissociation can be profound (Tronick & Weinberg 1997). In this state, pain-numbing endogenous opiates and behavior-inhibiting stress hormones, such as cortisol, are elevated. Blood pressure decreases, as does the heart rate, despite still-circulating adrenaline (Schore 2002). This ultimate survival strategy allows the baby to maintain basic homeostasis (Porges 1997).

When babies are in distress, their brains are at the mercy of these circulating chemicals. Hence, all their regulatory resources must be devoted to trying to reorganize and regain equilibrium (Tronick & Weinberg 1997). These kinds of biochemical alterations in a rapidly developing brain can have lasting consequences. In the infant, 'states become traits' so that the effects of early relational traumas become part of the structure of the forming personality (Perry et al 1995). This distress is all taking place at a time when the brain is at its maximum vulnerability to influences and stimuli. Hence, while this stress reaction is going on, the infant brain must devote all its resources to managing the stress and forfeits potential opportunities for learning at the critical periods of brain development (Schore 2001). Chronic shifts into this cycle of stress can cause brain impairment and damage (McEwen 2000).

It is then quite apparent that advising parents to allow their babies to cry and become distressed in an effort to get them to sleep is information which may place babies at risk. Babies are unable to make sense of a parent who is attentive at certain times of the day but unresponsive at others. Attachment research by Sroufe (1995) has shown that inconsistent or unresponsive care is associated with insecure attachments, suboptimal child development, cognitive and emotional functioning and mental health impairment. Additionally, neurological studies show that the pain of emotional separation registers the same way as physical pain (Panksepp 2003). The pain a baby experiences at being left alone to cry is truly quite intense.


If we want to teach our babies to regulate their emotions and behaviours, achieve mental health and gain the skills for happy, mutual relationships, we must do this through sensitive and responsive caregiving. This kind of caregiving in the first years of life becomes a powerful regulator of stress hormones and responses that follows a child throughout life (Gunnar & Cheatham 2003). Additionally, sleep training poses a threat to the attachment relationship by teaching parents to desensitise themselves to their baby's cues, promoting false understandings and lack of connection. When babies express distress but are met with non-responsiveness or rejection, they learn to divert the expression of their basic needs in order to preserve some sort of connection, thus losing authentic communication with their parent (Powell et al 2007). Parenting a child, the context in which it occurs and how well it is done is a human relationship that alters the characters of both partners in the relationship (Karen 1994). Thus, it is not just the baby, but also the entire relationship that is potentially jeopardised by sleep training. It is, therefore, by meeting our babies' needs that they learn healthy independence, including sleep independence.

Babies' sleep and sleeping arrangements should be approached with the utmost care, without subjecting babies to separations or non-responsiveness that lasts longer than they can manage. Families must choose what is appropriate for their unique circumstances, values and culture. Regardless of choice, however, we now have a substantial body of neurological, psychological and biological research to help frame that choice, allowing us to understand the critical importance of maintaining attuned connection to our babies, regardless of time of day.


Ainsworth MDS 1973, The development of infant-mother attachment. In Caldwell BM, Ricciuti HN (eds) The Integration of a Child Into a Social World. Cambridge University Press, London.

Anders TF 1994, Infant sleep, night-time relationships and attachment. Psychiatry 57: 11-21.

Anders TF, Eiben LA 1997, Pediatric sleep disorders: a review of the past 10 years. J Am Acad Child Adolesc Psychiatry 36: 9-20.

Anders TF, Taylor TR 1994, Babies and their sleep environment. Children's Environments 11: 123-134.

Anders TF, Halpern LF, Hua J 1992, Sleeping through the night: a developmental perspective. Pediatrics 90: 554-560.

Beebe B 2000, Co-constructing mother-infant distress: the microsynchrony of maternal impingement and infant avoidance in the face-to-face encounter. Psychoanalytic Inquiry 20: 214-240.

Bowlby J 1982, Attachment and Loss 1: Attachment. Basic Books, New York.

Brown M 1982, Corticotropin-releasing factor: actions on the sympathetic nervous system and metabolism. Endocrinology 111: 928-931.

Cozolino LJ 2006, The Neuroscience of Human Relationships. WW Norton, New York.

Davidson RJ 2000, Affective style, psychopathology and resilience: brain mechanisms and plasticity. Am Psychol 55: 1196-1214.

Ferber R 1986, Solve Your Child's Sleep Problems. Simon and Schuster, New York. reported by parents of Romanian orphans adopted to British Columbia. Int J Behav Dev 20: 67-82.

Fisher L, Ames EW, Chisholm K, Savoie L 1997, Problems reported by parents of Romanian orphans adopted to British Columbia. Int J Behav Dev 20: 67-82.

Fleming PJ, Blair PS, Bacon C, Bensley D, Smith I, Taylor E 1996, Environment of infants during sleep and risk of the sudden infant death syndrome: results of 1993-5 case-control study for confidential inquiry into stillbirths and deaths in infancy. BMJ 313: 191-195.

Gaylor EE, Goodlin-Jones BL, Anders TF 2001, Classification of young children's sleep problems: a pilot study. J Am Acad Child Adolesc Psychiatry 40: 61-67.

Gethin A, Macgregor B 2007, Helping Your Baby to Sleep. Finch Publishing, Sydney.

Gunnar MR, Cheatham CL 2003, Brain and behavior interface: stress and the developing brain. Infant Mental Health Journal 24(3): 195-211.

Hall T 2006, Save Our Sleep. Macmillan Press, Sydney.

Hofer MA 1996, On the nature and consequences of early loss. Psychosom Med 58(6): 570-581.

Hofer MA 2005, The psychobiology of early attachment. Clinical Neuroscience Research 4: 291-300.

Hogg T, Blau M 2002, Secrets of the Baby Whisperer. Ballantine Books, New York.

Karen R 1994. Becoming Attached: First Relationships and How They Shape our Capacity to Love. Oxford University Press, New York.

Keener MA, Zeanah CH, Anders TF 1989, Infant temperament, sleep organization and night-time parental interventions. In Chess S (ed) Annual Progress in Child Psychiatry and Child Development. Brunner/Mazel, New York.

Kobak R 1999, The emotional dynamics of disruptions in attachment relationships: Implications for theory, research and clinical interventions. In Cassidy J, Shaver PR (eds) Handbook of Attachment. Guilford Press, New York.

Marvin RS, Britner PA 1999, Normative development: The ontogeny of attachment. In Cassidy J, Shaver PR (eds) Handbook of Attachment. Guilford Press, New York.

McEwen BS 2000, The neurobiology of stress: from serendipity to clinical relevance. Brain Research 886: 172-189.

McKenna JJ 2001, Why we never ask 'is it safe for infants to sleep alone?' Academy of Breastfeeding Medicine News and Views 7(4): 32-33.

McKenna JJ, Mosko SS, Richard CA 1997, Bedsharing promotes breastfeeding. Pediatrics 100(2): 214-219.

McNamara P, Dowdall J, Auerbach S 2002, REM sleep, early experience and the development of reproductive strategies. Human Nature 13(4): 405-435.

Middlemiss W 2004, Infant sleep: A review of normative and problematic sleep and interventions. Early Child Development and Care 174: 99-122.

Nakao M 2006, The developing and learning brain during sleep. Sleep and Biological Rhythms 4: 2-3.

Panksepp J 2003, Neuroscience: feeling the pain of social loss. Science 10(302): 237-39.

Perry BD 2001, The neurodevelopmental impact of violence in childhood. In Schetky D, Benedek E (eds) Textbook of Child and Adolescent Forensic Psychiatry. American Psychiatric Press, Washington.

Perry BD, Pollard R, Blakely T, Baker W, Vigilante D 1995, Childhood trauma, the neurobiology of adaptation and 'use dependent' development of the brain: How 'states' become 'traits.' Infant Mental Health Journal 16: 271-291.

Porges SW 1997, Emotion: an evolutionary by-product of the neural regulation of the autonomic nervous system. Ann N Y Acad Sci 807: 62-77.

Powell B, Cooper G, Hoffman K, Marvin R 2007, The Circle of Security project: A case study--'It hurts to give that which you did not receive.' In Oppenheim D, Goldsmith DF (eds) Attachment Theory in Clinical Work with Children. Guilford Press, New York.

Richman N 1981, A community survey of characteristics of one to two-year-olds with sleep disruptions. J Am Acad Child Psychiatry 20: 281-291.

Roffwarg H, Muzio J, Dement W 1966, Ontogenetic development of the human sleep-dream cycle. Science 152: 604.

Sadeh A, Anders TF 1993, Sleep disorders. In Zeanah CH (ed) Handbook of Infant Mental Health. Guildford Press, New York.

Schore AN 2003, Affect Regulation and Disorders of the Self. Norton, New York.

Schore AN 2002, Dysregulation of the right brain: a fundamental mechanism of traumatic attachment and the psychopathogenesis of posttraumatic stress disorder. Aust N Z J Psychiatry 36: 9-30.

Schore AN 2001, Effects of a secure attachment relationship on right brain development, affect regulation and infant mental health. Infant Ment Health J 22(1-2): 7-66.

Schore AN 1994, Affect Regulation and the Origin of the Self: The Neurobiology of Emotional Development. Lawrence Erlbaum Press, New Jersey.

Segawa M 2006, Epochs of development of the sleep-wake cycle reflect the modulation of the higher cortical function particular for each epoch. Sleep and Biological Rhythms 4: 4-15.

Seymour FW, Brock P, During M, Poole G 1989, Reducing sleep disruptions in young children: evaluation of therapist-guided and written information approaches: a brief report. J Child Psychol Psychiatry 30: 913-918.

Siegel DJ, Hartzell M 2004, Parenting From the Inside Out. Penguin Press, New York.

Siegel DJ 2001, The Developing Mind. Guilford Press, New York.

Spitz R 1946, Hospitalism: A follow-up report on investigation described in Volume 1, 1945. The Psychoanalytic Study of the Child 2: 113-117.

Sroufe A 1995, Emotional Development: The Organization of Emotional Life in the Early Years. Cambridge University Press, Cambridge.

Tronick EZ, Weinberg MK 1997, Depressed mothers and infants: failure to form dyadic states of consciousness. In Murray L, Cooper PJ (eds) Postpartum Depression in Child Development. Guilford Press, New York.

Van Tassel EB 1985, The relative influence of child and environmental characteristics on sleep disturbances in the first and second year of life. J Dev Behav Pediatr 6: 81-86.

Lauren Porter BA MSW

Lauren Porter is a clinical social worker, consultant and psychotherapist, as well as Co-Director of the New Zealand-based Centre for Attachment. She holds a BA in East Asian Studies and a Masters Degree in Social Work.

Since receiving her MSW in 1995 she has been dedicated to working with families, children and adolescents in the field of mental health counseling and training. Lauren has worked in a wide range of settings and communities, including Germany and the US, in addition to New Zealand. Her experience has focused on families struggling with issues pertaining to conflict and trauma, including child sexual abuse.

Her current professional focus is the merging of attachment theory with neuroscientific data, with an eye toward the practical applications of everyday life. She is a member of the Attachment Parenting International Research Group, an Executive Committee member of Infant Mental Health Association Aotearoa New Zealand and a consultant for the 2006 and 2007 Nought to Five television series (TVNZ/Homegrown TV New Zealand). She is the mother of two children.

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