Abstract
In this dissertation, a cross-sectional primary group of N = 50 8- to 10-month-old infants, as well as a developmental comparison group of N = 32 5- to 7-month-olds, together with their caregivers, completed two tasks: a caregiver context task to test caregivers (here, mothers) as a mechanism of infant neural and physiological regulation, and a freeplay task to test caregiver behavior as a moderator of their regulatory impact. In the physiology task, we measured the impact of caregiver presence on infant neural and physiological response to threat. Infant-caregiver dyads viewed a series of threatening and non-threatening stimuli twice: once while sitting on their caregiver’s lap, and once while sitting in a high chair with their caregiver out of sight. During the task, we measured PFC response using functional near infrared spectroscopy (fNIRS), a non-invasive measure of neural blood flow akin to fMRI but allowing for infant movement. The eyeblink startle reflex, which is mediated through (Hitchcock & Davis, 1987) and correlated with (van Well et al., 2012), amygdala activity, was used as a novel proxy measure of amygdala response. Infant-caregiver dyads were also recorded in a 5-minute free play session from which coded for two caregiver behaviors: sensitivity and cooperation. Sensitivity and cooperation are established measures of caregiver behavior that gauge the promptness and appropriateness of a caregiver’s response to their infant’s needs, and the extent of caregiver interference with the infant’s exploration—both have a known impact on developing self-regulation (e.g., Leerkes et al., 2009). Consistent with current theory (Callaghan & Tottenham, 2016; Coan & Sbarra, 2015; Tottenham, 2020), we hypothesized that, during threat, caregiver presence would 1) decrease threat responding through decreased amygdala response, 2) change self-regulation of threat responding through altered mPFC response, and 3) that each of these effects would be greater among infants whose caregivers show greater positive caregiving behavior. Our findings confirmed the second hypothesis: caregiver presence reduced mPFC responding to threat among 8- to 10-month-olds. In contrast, caregiver presence did not alter infant amygdala responding to threat, but instead increased amygdala response to the non-threat/reward stimulus. Further, caregiver behavior was not associated with the impact of caregiver presence as hypothesized, but was positively associated with infant neural responding more generally. These findings reveal the novel possibility that caregiver-provided facilitation of access to reward may be an important additional avenue through which caregivers serve to scaffold advantageous neuroregulatory brain development.
