The Development of Social Perception Networks in Low- and Middle-Income Infants: Longitudinal Assessments of fNIRS Background Functional Connectivity

Shortly after birth, human infants demonstrate behavioural selectivity to social stimuli. However, the neural underpinnings of this selectivity are largely unknown. Here we examine patterns of functional connectivity to determine how regions of the brain interact while processing social stimuli and how these interactions change during the first two years of life. Using functional near-infrared spectroscopy (fNIRS), we measured functional connectivity at 6 (n = 183) and 24 (n = 123) months of age in infants from Bangladesh who were exposed to varying levels of environmental adversity (i.e., low- and middle-income cohorts). We employed a background functional connectivity approach that regresses out the effects of stimulus-specific variables known to affect functional connectivity. At 6 months, the two cohorts had similar fNIRS patterns, with moderate connectivity estimates for regions within and between hemispheres. At 24 months, the patterns diverged for the two cohorts. Global (brain-wide) connectivity estimates increased from 6 to 24 months for the low-income cohort and decreased for the middle-income cohort. In particular, connectivity estimates among regions of interest (ROIs) within the right hemisphere decreased for the middle-income cohort, providing evidence of neural specialization by two years of age. These findings provide insights about the impact of early environmental influences on functional brain development relevant to the processing of social stimuli.