Electrophysiological Assessment of Visual Pathways in Children with and without Autism Spectrum Disorder
Weinger, Paige Mariel
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Purpose: A battery of neurophysiological tests were designed and implemented using visual evoked potentials (VEP) to examine specific neural mechanisms that may underlie autism symptomotology. Although previous studies have identified perceptual abnormalities in children with autism spectrum disorder (ASD), the early stages of visual processing remain underexplored. Traditional VEP techniques were adapted to assess early-stage visual processing in a sample of children with ASD, typically developing children, and unaffected siblings.;Methods: Transient and steady-state VEP recordings were obtained from 14 children with ASD (Mage = 8.64, SD = 2.53), 15 typically developing children (Mage = 7.75, SD = 2.47), and 5 unaffected siblings (M age = 6.00; SD =1.58) using a Neucodia system (VeriSci Corp.). In short-duration runs, each stimulus condition was presented for ~2 s and the electroencephalogram (EEG) was recorded synchronized to the display's frame rate. Stimulus conditions (10x10-deg field) included a contrast-reversing checkerboard (100% contrast) to elicit a transient VEP (tVEP), which enabled the examination of multiple frequency mechanisms, a pair of radial patterns (partial-windmill and windmill-dartboard) with dynamic elements contrast-reversed at ~4 Hz (32% contrast) to elicit steady-state VEPs (ssVEP) that quantify nonlinear lateral inhibitory interactions, and a dartboard with each element contrast-reversed by a sum of two high-frequency sinusoids (22.8 and 24.8 Hz, 32% contrast/sinusoid) to yield an intermodulation response at 2 Hz that reflects excitatory nonlinear interactions. In addition, contrast-sweep conditions (bright or dark isolated-checks) in which contrast increased in octave steps from 2-64% elicited ssVEPs at 12.5 Hz to assess ON/OFF pathways, respectively.;Results: Differential effects were observed across stimulus conditions. Children with ASD and unaffected siblings both displayed deficits in low contrast responses, particularly under conditions that emphasize contributions from the magnocellular pathway. Increased neural noise was also observed in both the ASD and unaffected sibling groups. In contrast, the ASD group displayed evidence of strong GABAergic inhibition and enhanced short-range lateral interactions. No differences were observed in the excitatory contributions to the VEP in response to the two-sinusoid condition.;Conclusions: Findings demonstrate that short-duration stimuli, in conjunction with multivariate statistical analysis of the brain's responses, can yield sensitive and objective indices of the neural pathways under investigation. Short-duration VEPs hold promise as a rapid and reliable method to examine electrophysiological biomarkers, or endophenotypes, of ASD.
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