Neural Responses to Biological Motion at 3 Months: A Functional Near-Infrared Spectroscopy (fNIRS) Study Comparing Infants at Low and High Risk for Autism

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 engagement. The network of brain regions involved in biological motion processing—including the posterior superior temporal sulcus (pSTS)—consistently shows dysfunction in autism as compared to typical development. The early development of this neural system, however, is not well understood, in part because of practical difficulties in the neuroimaging of awake infants. Functional near-infrared spectroscopy (fNIRS) is well-suited to overcome these limitations. Recent work (Lloyd-Fox et al., 2013) has demonstrated that 4- to 6-month-old infants at high risk for autism show less selective neural responses to biological motion than low-risk infants, however it is unclear whether these differences are present in the first 3 months of life. Examining the early neural correlates of biological motion processing could elucidate the brain bases of ASD.

Objectives:   We examined the neural underpinnings of biological motion processing at 3 months of age to determine whether neural differences exist in infants who are at high risk (HR) versus low risk (LR) for ASD at this early age.

Methods:   Infants were defined as high-risk if they had an older sibling with autism. We monitored regional cerebral blood oxygenation changes using a 24-channel NIRS apparatus over bilateral temporal cortex to investigate brain activity while infants viewed 10s video clips of biological and scrambled motion PLDs. Infants were video-recorded so that looking time could be assessed offline, frame-by-frame. Preprocessing included low- (0.7 Hz) and high-pass (0.01 Hz) filtering, and exclusion of trials containing evidence of excessive motion and/or looking time of less than 75 percent.

To date, participants include 6 LR infants and 5 HR infants, matched on age (LR: M = 3.42 months, SD = 0.52; HR: M = 3.53 months, SD = 0.47). We calculated changes in oxy-Hb in each recording channel for integrated blocks of biological and scrambled trials. We then averaged measurements for each hemisphere separately to obtain waveforms representing the infants’ neural response to biological and scrambled motion in left and right temporal regions.

Results: In the right temporal region, the differential response to biological versus scrambled motion was marginally greater in LR infants between 7–10 seconds post-stimulus onset (t(9) = 1.75, p = 0.11). Interestingly, this difference between LR and HR infants was driven by a deactivation to scrambled motion in the low-risk infants. We expect these findings to reach significance with a larger sample.

Conclusions:  These findings suggest that the neural mechanisms for processing biological motion are present in the first 3 months of life in typical development and show atypical patterns in infants at risk for autism by 3 months. Although only a fraction of the HR 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, which, crucially, is present prior to the onset of clear behavioral symptoms.