Caregiver Cumulative Cortisol Mediates Deviations in Functional Connectivity in Infants: A Novel fNIRS Study

The effects of chronic physiological stress on the developing infant brain have long been recorded by developmental scientists. Infants who have experienced chronic physiological stress, as elucidated from maternal physiological stress, have been found to have deviations from the "typical" developing brain's trajectories (Troller-Renfree, 2020). These alterations, usually consisting of an overabundance of low frequency EEG power and a relative paucity of high-frequency power, have been attributed to a developmental delay entitled the "maturational lag" which has been postulated to describe a delay in the development of central nervous system, and in particular, cortical development (Corning, Steffy, Anderson & Bowers, 1986). My past research has extended these findings, looking into the differentiations between EEG power growth curves of infants mediated by chronic caregiver stress and its implications on cortical development. Not much research has been done using functional brain imaging techniques to determine whether these electrophysiological and structural changes are also marked by changes in hemodynamic responses as well when comparing infants with caregivers with and without chronic stress, and my proposed research aims to be some of the first research to do so.
Functional near infrared spectroscopy (fNIRS) is a relatively novel method in which scientists can elucidate data about the hemodynamic changes happening in the brain. Though fMRI is the most commonly used technique to study these changes, its bulky and static nature makes it difficult to use on infants. fNIRS is comparatively smaller and portable, and much more suited to research in infancy.This method makes inferences about the brain's cytoarchitecture by examining values of connectivity/synchrony between neurons as they communicate with each other across the brain. Many of these studies have been done using fMRI, but more recently, scientists have begun to use fNIRS to study functional connectivity in infants. Much of this research has been done in cases of psycho- and neuropathology, but non-pathological literature also exists.
To gain more information about the changes that occur to the infant brain when impacted by chronic stress, and to find more information either confirming or challenging the maturational lag hypothesis, I propose that a differential functional connectivity study be carried out, comparing infants with caregivers with chronic stress with those with infants with caregivers without. Will caregiver stress influence functional connectivity development in infants?
This study fits very well into the PIPKIN project that is currently ongoing within the Cambridge Baby Lab, which includes fNIRS scanning at one/two weeks post-birth, at 5 months and at 9 months. Caregiver stress will be determined via hair cortisol. Hair cortisol has been found to be a reliable measure of chronic stress levels (Ursache et al., 2017) and allows us to make inferences about the stress that the infants we study experience, without using an invasive measure to determine their cortisol levels. An appropriate pipeline must be determined for the description of fNIRS functional connectivity but for now I point to the methods used in Gao et al., 2014, which identified 9 functional networks in fcMRI and was able to make inferences about their relative maturation via 3 quantitative measures: within-network connectivity, outside-network connectivity and overall similarity to adult references. After collection of resting data from each infant, and collecting hair samples from the caregiver, I will conduct a statistical analysis comparing the groups (high hair cortisol against low hair cortisol) to determine whether any significant differences arise between them in each functional network as well as carry out power analyses to determine whether correlations occur between magnitude of potential difference and difference in hair cortisol levels.