Neural Responses to Biological Motion in the First Year of Life: A Functional near-Infrared (fNIRS) Study Comparing Low- and High-Risk Infants

Background: From birth, human infants preferentially attend to point-light displays (PLDs) of biological motion over scrambled motion (Simion, Regolin, & Bulf, 2008), suggesting an evolutionarily-conserved mechanism to support social attention and engagement from birth. The posterior superior temporal sulcus (pSTS) is a key node in a network of brain regions involved in biological motion processing in typical children and adults and shows dysfunction in autism (Kaiser et al., 2010). At present, the early development of this neural system is not well understood. Functional near-infrared spectroscopy (fNIRS), which measures oxygenated (oxy-Hb) and deoxygenated hemoglobin concentrations in cortical brain regions, is ideally suited to measure correlates of brain activity in awake infants.

Objectives: fNIRS studies of biological motion processing in infants have been limited to a narrow age range of typically-developing infants (Lloyd-Fox et al., 2009, 2011). We are charting the typical development of the neural underpinnings of biological motion processing across the first year of life and attempting to determine at what age neural differences emerge in infants who go on to develop autism.

Methods: In this prospective, longitudinal study, infants at low and high risk for autism completed fNIRS experimental measures at 3, 6, 9, 12, and 18 months, with provisional diagnoses at 24 months and confirmatory diagnoses at 36 months. Infants were defined as “high-risk” if they had an older sibling diagnosed with autism. We monitored regional cerebral blood volume changes using a 24-channel NIRS apparatus over bilateral temporal regions to measure brain activity while infants viewed 10s video clips of PLDs of biological and scrambled motion. Infants were video-recorded so that looking time could be assessed off-line, frame-by-frame. Preprocessing included low (0.7 Hz) and high-pass (0.01 Hz) filtering and exclusion of trials containing excessive motion and/or visual attention less than 75 percent.

Results: To date, participants include 8 low-risk (LR) infants and 8 high-risk (HR) infants, matched on age (LR: M = 6.20 months, SD = 2.19; HR: M = 6.69 months, SD= 2.41). We calculated changes in oxy-Hb in each channel for integrated blocks of biological and scrambled trials. We then averaged channels in the left and right hemispheres separately to obtain waveforms representing the infants’ neural response to biological and scrambled motion in bilateral temporal regions. While low-risk infants differentiated robustly between biological and scrambled motion in the right temporal region between 5-12 seconds post-stimulus onset, high-risk infants showed no difference between conditions during this time window.

Conclusions: These findings suggest that the neural mechanisms for processing biological motion are present in the first 9 months of life in typical development and show dysfunction in infants at risk for autism by 9 months, prior to the onset of any clear behavioral indications of autism. Although statistically only a fraction of the high-risk infants will go on to develop autism, lack of differentiation between biological and scrambled motion in this group may represent a neuroendophenotype or genetic liability to develop autism.