Crankiness and Irritability
Until now I’ve been very proud of having the perfect kid....Now she’s very cranky and
crying all the time.Irritability, including crying and fussing behaviors, is a highly visible attribute of
infancy. The occurrence of these behaviors progressively rises across early infancy
to peak in the second month, followed by a gradual decline (Brazelton 1962 ). The
commonality of this pattern among healthy infants has made irritability a“normal”
aspect of early development (Wessel et al. 1954 ), with caregiver responsivity to
cries viewed as a critical component of early attachment formation (Swain et al.
2004 ). Crying and other behavioral outbursts are sources of anxiety and concern for
caregivers (Beebe et al. 1993 ), and several studies have examined behavioral
outbursts in an attempt to classify whether they are developmental or clinical in
nature (Barr 1990 ). Sources of these episodes may include a lack of responsiveness
to the child (Crockenberg and Smith 2002 ) or an immature gastrointestinal system
(Cirgin Ellett 2003 ). Some of these experiences may be physiologically rooted in
the hormonal milieu surrounding discrete growth events, representing combined
maturational shifts in the nervous and skeletal systems through neuro-humoral and
endochondral responses, respectively.
The Biobehavioral Growth Trajectory
Behavioral correlates of physical growth are common among parental narratives.
Beyond a side effect of chemical messengers involved in growth saltations, there is
a larger frame in which growing is a lived experience. Development has the phe-
notypic characteristic of overtly evident changes, as neuromuscular and cognitive
maturation manifest in the acquisition of new skills and characteristics (Adolph and
Tamis-LeMonda 2014 ), and both children and their parents delight in new com-
petencies that emerge in due course. The notion that development proceeds
episodically with behavioral changes that emerge with maturational reorganization
wasfirst described by René Spitz and further elaborated in the concept of a
biobehavioral developmental trajectory (Emde et al. 1976 ). The idea that coordi-
nation and integration exists across both somatic and psychological systems
embodies scientifically the nature of the subjective experiences that parents describe
when they notice the sudden changes in their infant’s behaviors—the appearance of
smiling at about two months of age and stranger anxiety, for example, at eight
months of age. Whether saltatory growth is a unifying developmental program by
which physical growth and behavioral development cross talk is yet to be empir-
ically documented.
Research aiming to assess the temporal relationship between physical growth
and behavioral development is limited. In infancy, the Bayley Scales of Motor and
Mental Development was used to explore associations between motor, social, and
58 M. Lampl et al.