Neural Responses to Familiar and Unfamiliar Faces in Infants At High Risk for ASD: A near-Infrared Spectroscopy Study

Background: Neuroimaging work has provided evidence of atypical brain activity in response to faces in individuals with autism spectrum disorder (ASD) as well as in their first-degree relatives.  Prospective work examining infants with an older sibling with ASD provides an opportunity to look for early neural markers of atypical face processing, some of which might relate to the broader autism phenotype and others that might be predictive of later ASD outcome.

Objectives: The present work examined neural responding to familiar and unfamiliar faces in high- and low-risk infants using near-infrared spectroscopy (NIRS), a state-of-the-art optical imaging technique, to see how these responses might relate to the broader autism phenotype.

Methods: As part of a longitudinal study of infant siblings of children with ASD and typically-developing children, NIRS was used to measure hemodynamic responding in 9-month-olds while they viewed 16s videos of their mother and a stranger displaying a neutral expression.  A 24-channel Hitachi ETG-4000 NIRS system was used to record changes in oxyhemoglobin (oxyHb) and deoxyhemoglobin (deoxyHb) over frontal and right-temporal regions.  Analyses focused on mean oxyHb and deoxyHb responses to mother and stranger in an 8s time window beginning 4s after stimulus onset.  Thirteen low-risk control infants (LRC) and eight infants at high risk for ASD (HRA) contributed two or more artifact-free trials for mother and for stranger and were included in the present analyses.  

Results: In examining oxyHb responses to mother and stranger over right lateral regions, analyses revealed a main effect of identity (p = .04), such that infants show greater (more positive) responses to mother (M = .013 mm*mol) than stranger (M = -.035 mm*mol), and a main effect of group (p = .019), such that LRC show greater responding (M = .018 mm*mol) than HRA (M = -.040 mm*mol).  In frontal regions, a marginally significant interaction between identity and group was found for oxyHb responding (p = .06).  When explored further, LRC infants showed significantly greater oxyHb responses to mother (M = .042 mm*mol) than stranger (M = -.025 mm*mol) in frontal regions (p = .025), while HRA showed no difference between mother (M = -.020 mm*mol) and stranger (M = -.010 mm*mol; p = .70). 

When examining deoxyHb, frontal regions showed a main effect of identity (p = .022), with greater (more negative) deoxyHb responding to mother (M = -.012 mm*mol) than stranger (M = .018 mm*mol).  DeoxyHb also showed a trend towards greater responding in LRC (M = -.009 mm*mol) as compared to HRA (M = .014 mm*mol) in the frontal region (p = .1).  No main effects or interactions were found when for deoxyHb responding in right lateral regions.

Conclusions: By 9 months, hemodynamic responses to familiar and unfamiliar faces reveal evidence of atypicality in infants at high risk for ASD which might relate to the broader autism phenotype.  These infants will be followed longitudinally, and future work will explore relations between these early neural measures of face processing and later ASD diagnosis.