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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

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