Early Visual Processing of Faces in Tuberous Sclerosis Complex (TSC) and in Children Showing Early Signs of ASD

Background:

Tuberous sclerosis complex (TSC) is a rare genetic disorder that confers a high risk for autism spectrum disorder (ASD), at a rate of 60% (Jeste, 2013). ASD is characterized by core deficits in social interaction and communication. EEG studies have revealed that children with ASD process faces differently when compared to children with typical development (Dawson, 2002; McCleery, 2009). Therefore, studying socially relevant stimuli, such as faces, may be an adequate way to measure atypical cognitive mechanisms in children with neurodevelopmental disorders, such as ASD and TSC. Not much is known about face processing in children with TSC, nor about how they process faces compared to ASD.

Objectives:

We asked whether EEG correlates of face and object processing differentiated four groups of 12-24 month-old toddlers at risk for ASD: 1. toddlers with TSC who had ASD outcomes (TSC/ASD), 2. toddlers with TSC without ASD outcomes (TSC/noASD), 3. toddlers showing early behavioral signs of ASD (HR) based on elevated scores on the Autism Diagnostic Schedule-Toddler Module (ADOS-T), and 4. low risk controls (LR).

Methods:

A cohort of 7 TSC/ASD toddlers, 11 TSC/noASD toddlers, 24 HR toddlers who scored in the moderate-to-severe risk range on the ADOS-T, and 28 LR toddlers were shown images of faces and objects in a randomized order while high-density EEG was recorded (128-electrodes, EGI Inc.). Event-related EEG components of interest were the N290 (peak amplitude and latency), P400 (peak amplitude and latency), and Nc (mean amplitude).

Results:

There were significant main effects of condition (F(1,66)=3.86, p=.05) and region (F(2,65)=9.14, p<.001) for the N290 peak amplitude, as well as significant condition by region (F(2,65)=5.255, p=.008) and condition by region by group (F(6,132)=2.589, p=.008) interactions. Post-hoc tests revealed regional differences, showing greater minimum N290 amplitude in the right (M=5.10) region than the left (M=3.57, p=.036). Post-hoc tests also showed differences in condition in the right region within the HR group only, suggesting greater responses to faces (M=9.15) than to objects (M=9.00, p=.047) in early visual processing. For P400 peak amplitude, there were significant main effects of condition (F(1,66)=8.73, p=.004) and region (F(2,65)=3.79, p=.028). There was a main effect of condition for Nc mean amplitude (F(1,66)=24.35, p=.001). There was a significant main effect of group in P400 latency to faces, with slowed processing in both TSC groups (TSC/ASD=446.17ms; TSC/noASD=440.28ms), compared to HR and LR (HR=396.77ms; LR=410.542ms; p=.002).

Conclusions:

Condition effects in the three components indicate that there was electrophysiological differentiation of faces and objects across all groups. The HR group showed differentiation in the early visual component N290, which may reflect visual processing mechanisms unique to ASD. The delayed face processing seen in P400 in the TSC group was not specific to ASD diagnosis and, therefore, may reflect a more fundamental delay in processing of social information that could have implications for social skills for all children with TSC. Further investigation of developmental outcomes and correlation of EEG patterns with social communication skills in TSC may shed light on the impact of delayed face processing in this high-risk cohort.