affective development (e.g., head control, sitting, social smile) with head circum-
ference growth saltations, with a 76% agreement among individual infants (Lampl
and Emde 1983 ). This type of work has been rare to date as other investigations
examining growth and behavioral development concordance have been hampered
by assumptions of skeletal growth as a continuous process (Lasky et al. 1981 ).
Notions regarding associations between brain growth and mental development
(Epstein1974a,b) were directly dismissed (McCall et al. 1983 ) based on data that
were inadequate to test the hypothesis due to infrequent growth data collection. In
the absence of daily growth data, saltatory growth events cannot be identified. The
default is that changes in size are attenuated across time and appear to be a slow and
continuous process, just like the growth curve. Documenting biobehavioral
developmental shifts concordant with growth events is a challenge. It requires
methodological rigor to ensure accurate identification of the timing of discrete
saltations and sufficient details regarding behaviors to identify unique features.
Puberty, a recognized period of rapid growth, provides a useful model for the
relationship between growth and psychobiological shifts. The hormonal changes
that occur over pubertal development are directly correlated with alterations in
behavior via the modulation of brain circuits (Cameron 2004 ; Sisk and Foster
2004 ). The pubertal awakening of the reproductive axis is dependent upon the
signaling of gonadotropin-releasing hormone (GnRH) , which controls the syn-
thesis and secretion of the gonadotropins (LH and FSH) , which then feedback to
neural receptors and remodel the adolescent brain. Indeed, gonadal steroids mod-
ulate the activity of several neurotransmitter systems which play central functions in
cognitive function and emotional regulation (van Wingen et al. 2011 ), explaining
many of the altered behaviors commonly observed during puberty. The mecha-
nisms by which these events occur mirror early brain development and include
progressive and regressive processes (Sisk and Zehr 2005 ), offering an excellent
and robust prototype for earlier, similar joint psychophysical growth relationships.
Further understanding the temporal relationship between behavioral attributes
and skeletal growth requires precision and accuracy for both levels of measurement.
This necessitates a mixed methods approach that integrates daily anthropometric
data together with detailed experiential data from open-ended interview questions
and detailed narrative logs with temporal specificity to identify correspondence with
saltatory growth, concomitant behaviors, and any other physiological biomarkers.
In order to capture saltatory growth, anthropometric assessments must be daily or
the time-specificity is lost and growth events are attenuated across time. Parallel
data collection by both objective and subjective methods enables the investigation
of behavioral linkages to growth events. Parental reporting of infant sleep durations
permitted the scientific documentation that, indeed, just as parents perceive, babies
sleep more right before and while they are growing in length (Lampl and Johnson
2011a). The same parental records have documented appetite changes and behav-
ioral agitation as co-occurrences with measured saltatory length growth.
4 The Lived Experience of Growing 59