The full scope of oxytocinergic influences on the parental brain: Maternal
defensiveness and grandparent-child interactions

Children require extensive parental care and protection during infancy. Upon
childbearing, caregivers need to be able to flexibly change from nurturing and
affiliative behaviors to protective behaviors to defend the immature offspring.
Such plasticity in behavioral tendencies has been suggested to be supported by
dedicated neural and neuroendocrinological systems of which the neuropeptide
oxytocin, in particular, has been suggested to be central in mediating
parenting behaviors. Animal studies have shown that the oxytocin system is
associated with the level of maternal care and affiliation toward the offspring
and also with aggression and defensive reactivity when the offspring are
threatened. In humans, evidence is likewise accumulating to show the importance
of oxytocin in promoting parental caregiving sensitivity towards and
affectionate interactions with infants. No research to date, however, has been
conducted on the potential role of oxytocin in promoting protective behaviors
and defensive aggression in threatening contexts in the parents of human
infants. In addition, the role of the oxytocin system in grandparent-grandchild
interactions is largely neglected. Thus, to gain a comprehensive picture of the
neural bases of (grand)parenting behaviors in humans, research is needed to
investigate the role of oxytocin in influencing parental and grandparental
reactions to their (grand)children. By testing infants, mothers, and
grandmothers simultaneously, the project will tackle these issues.

Our primary aims are 1) to test with observational and electrophysiological
techniques whether intranasal oxytocin administration to mothers of young
infants increases their defensive reactivity and protective approach responses
in mildly threatening contexts, and 2) to expand the current field of research
on oxytocin to ageing populations by measuring whether intranasal oxytocin
administration increases grandmothers* sensitivity towards their grandchildren
similarly as in parents. The secondary aims are to measure the concordance in
all participants* salivary oxytocin levels and to assess the mothers* and
grandmothers* attachment representations of one another and the potential
modulation of such representations by oxytocin administration.

A placebo-controlled, double-blind, within-subjects design with two laboratory
visits is used to measure the influence of oxytocin on mothers* defensive
reactivity and grandmothers* sensitivity to their grandchildren.

The participants will take part in two identical laboratory sessions one month
apart which differ only by the content of the intranasal substance (oxytocin
vs. placebo). The laboratory sessions consist of an observational paradigm (the
Enthusiastic Stranger Paradigm; ESP), a recording of electroencephalography
(EEG) from the mother, assessments of caregiving sensitivity with both the
mother and the grandmother, collection of saliva samples to measure the
participants* salivary oxytocin levels, and short questionnaires to measure the
participants* attachment representations. The ESP is a semi-naturalistic
observational paradigm in which an unfamiliar adult (a trained member of the
research team) approaches the infant in a slightly intrusive manner and may
trigger defensive/protective responses from the mother (e.g., hypervigilance,
verbal or behavioral attempts to interrupt the stranger). In the EEG task, we
will use a subliminal affective priming paradigm to investigate whether
oxytocin increases mothers* approach responses (measured with frontal EEG
asymmetry in the alpha frequency band) and vigilance/attentiveness (measured
with event-related brain potentials) toward images of their own vs. an
unfamiliar infant after being primed by pictures depicting social threat. The
grandmother*s sensitivity to her grandchild will be measured during the
mother*s EEG recording and the mother*s sensitivity will be measured at the end
of the laboratory session.

The study will include two visits to the Centre for Child and Family Studies,
Leiden University, both of which will last less than 2 hours. The mother will
undergo an EEG measurement for ca. 20 minutes. Other measures include
observational measures for assessing caregiving sensitivity (mothers and
grandmothers) and maternal defensive reactions (the ESP), and saliva samples (3
per session) for assessing the levels of salivary oxytocin. Oxytocin and
placebo are administered intranasally (1 puff of nasal spray to each nostril)
to the mother and grandmother. The experimenters need to be in physical contact
with the participants: 1) the ESP includes an experimenter gently touching the
infant and 2) preparation of the EEG requires physical contact with the mother.
These forms of physical contact pose no risks to the participants and are
painless. The ESP includes a brief encounter with a mildly intrusive stranger.
Some of the mothers may experience this as uncomfortable. It is, however, part
of the nature of this paradigm to be mildly uncomfortable to trigger the
mother*s motivation to interrupt the stranger.