Research: Oxytocin and mutual communication in mother-infant bonding

Attachment theory has become one of the dominant models for understanding the etiology of mental illness. More and more, we are finding that the caregiver-infant bond is crucial in the later mental health of the child. There are many factors that influence this bonding, including the attachment wounds of the caregiver, environment, genetics, and a host of other factors, including the biology of child and caregiver.

One of the primary biological factors (which also is determined by many other variables) is oxytocin. This new study looks at the role of oxytocin in bonding, which we know to be crucial while not yet understanding the mechanisms involved.

The article is open access, from Frontiers in Human Neuroscience.

Oxytocin and mutual communication in mother-infant bonding

Miho Nagasawa, Shota Okabe, Kazutaka Mogi and Takefumi Kikusui*

• Department of Animal Science and Biotechnology, Azabu University, Sagamihara, Kanagawa-ken, Japan

Mother-infant bonding is universal to all mammalian species. In this review, we describe the manner in which reciprocal communication between the mother and infant leads to mother-infant bonding in rodents. In rats and mice, mother-infant bond formation is reinforced by various social stimuli, such as tactile stimuli and ultrasonic vocalizations (USVs) from the pups to the mother, and feeding and tactile stimulation from the mother to the pups. Some evidence suggests that mother and infant can develop a cross-modal sensory recognition of their counterpart during this bonding process. Neurochemically, oxytocin in the neural system plays a pivotal role in each side of the mother-infant bonding process, although the mechanisms underlying bond formation in the brains of infants has not yet been clarified. Impairment of mother-infant bonding, that is, deprivation of social stimuli from the mother, strongly influences offspring sociality, including maternal behavior toward their own offspring in their adulthood, implying a “non-genomic transmission of maternal environment,” even in rodents. The comparative understanding of cognitive functions between mother and infants, and the biological mechanisms involved in mother-infant bonding may help us understand psychiatric disorders associated with mother-infant relationships.

Citation: Nagasawa M, Okabe S, Mogi K and Kikusui T. (2012). Oxytocin and mutual communication in mother-infant bonding. Frontiers in Human Neuroscience, 6: 31. doi: 10.3389/fnhum.2012.00031

I am including the introduction to entice you to go read the whole article.

Introduction

“Sympathy is much strengthened by habit. In however complex a manner this feeling may have originated, as it is one of high importance to all those animals which aid and defend one another, it will have been increased through natural selection; for those communities, which included the greatest number of the most sympathetic members, would flourish best, and rear the greatest number of offspring” (Charles Darwin, “Descent of Man,” 1871).

During the process of mammalian evolution, animals developed sympathetic neural and behavioral systems, in which for example, weak and helpless member of individuals are protected and nurtured by other group members. This phenomenon is mostly clearly observed in mother-infant relationship, such as mother infant bonding (Broad et al., 2006).

Social bonds like mother-infant bonding are hypothetical constructs and cannot be measured directly. However, there are several behavioral and physiological measures that have been used as indices of social bonding, including increased physical proximity (Hennessy, 1997), behavioral distress, or elevated corticosteroid levels following separation from the bonding partner (Ziegler et al., 1995; Norcross and Newman, 1999). Social bonding has not yet been clearly defined, but it has been proposed that social bonding can be distinguished neurochemically from social affiliation, in which corticosteroid elevation does not occur following separation (DeVries, 2002). Moreover, subsequent reunion with conspecific animals ameliorates separation distress or aversive experiences. This phenomenon is termed as “social buffering” (Kikusui et al., 2006); its effect depends on the degree of affiliation with the partner and is strongest with the bonding partner, such as that seen in the dyad of mother-infant.

Mother-infant bonding is unique with respect to its influence on the offspring's future. This idea was first suggested in humans by Bowlby's attachment theory (Bowlby, 1969). Subsequently, many psychological and animal research studies have reported that child abuse or childhood neglect are correlated with severe, deleterious long-term effects on the child's cognitive, socio-emotional, and behavioral development (Hildyard and Wolfe, 2002). The developmental effects of mother-infant bonding have also been indicated experimentally in non-human primates. For example, in a study by Winslow et al. (2003), mother-reared and human nursery-reared monkeys were subjected to a novel environment with or without a cage mate. The monkeys reared by their mothers exhibited a reduced cortisol response when a social partner was available, whereas nursery-reared monkeys did not. In nursery-reared monkeys, social contact, such as allogrooming and inter-male mounting, was drastically reduced. These findings suggest that the social buffering effect is impaired as nursery-reared monkeys had experienced less social contact in a novel environment. Thus, impairment of mother-infant bonding strongly influences offspring sociality in human and non-human primates (Agid et al., 1999; Heim and Nemeroff, 2001), although details of the underlying mechanisms are not yet fully understood. Additionally, because the bonding formation is established during the process of social communication between mother and infants, social cognition has a pivotal influence on the bonding process (Ross and Young, 2009). However, little information has been obtained regarding the role of each social cue in the formation of bonds.

In the present review, we describe the manner in which mutual communication between mother and infant leads to mother-infant bonding in rodents. We emphasize the significance of the conserved oxytocin neural system in mother-infant bond information, with several studies having shown that oxytocin plays a fundamental role in establishing this bond (Kendrick, 2000; Young et al., 2001; Wang and Aragona, 2004; Young and Wang, 2004). Other neurotransmitters that regulated social bonding, such as opioids and dopamine are also important, however, we would concede these issues in other articles. We also review the effects of deprivation of mother-infant bonding, by studying the consequences of early weaning on neurobehavioral development in rodent offspring. Intensive maternal care has evolved and has been preserved, uniquely in mammals, and it is highly probable that mother-infant bonding is universal to all mammalian species. These comparative points of view provide insights into the biological significance of mother-infant bonding in mammals; a comparative understanding of the developmental consequences of this bonding and its underlying mechanisms, even in rodents, may help in our treatment or prevention of disorders associated with child abuse or childhood neglect (Agid et al., 1999; Heim and Nemeroff, 2001).