Children with ASD Fail to Downregulate Visual Cortex during Auditory Processing

Background:  Autism Spectrum Disorders (ASD) are predominantly characterized by impairments in two core domains: social communication, and restricted and repetitive behaviors (RRB) that encompass atypical responses to sensory stimuli. Research has indicated a high prevalence of sensory issues in ASD; some children with ASD are easily overwhelmed while others seem unaware of their environment. Given the importance of sensory input during development, particularly from vision and audition (two of the main sensory modalities involved in social interactions and language), impairments in these systems may have cascading effects that contribute to disturbances in higher-order cognitive and sociocommunicative abilities.

Objectives:  We assessed the neural mechanisms underlying basic sensory processing of visual and auditory information in ASD. Specifically, we examined the effects of auditory processing on visual cortical activity in nonlinguistic contexts.

Methods:  Functional magnetic resonance imaging (fMRI) was used to test children and adolescents with ASD (n = 16) and typically developing (TD) participants (n = 16) matched for age, gender, nonverbal IQ, and handedness during a sensory discrimination task. Participants were presented with visual (dot located high or low in the display) and auditory stimuli (4000 or 1600Hz), and were instructed to indicate whether each stimulus was “high” or “low”. Measures of accuracy and reaction time were also recorded during the scan.

Results:  Functional MRI findings indicated divergent patterns of activity in visual cortex during auditory processing. The TD group showed downregulation, whereas the ASD group showed upregulation in visual cortical areas, which was associated with symptomatology. Moreover, ASD children and adolescents had lower auditory discrimination accuracy than their TD counterparts.

Conclusions:  Our findings (i) support the notions of basic auditory impairment, but visual sparing in ASD. They further indicate (ii) that individuals with ASD fail to downregulate visual cortex during simple auditory processing, and (iii) that this impaired crossmodal modulation is linked to sociocommunicative symptomatology. These results add to the existing evidence of atypically enhanced recruitment of visual cortices during a variety of cognitive and perceptual tasks (Samson et al., Hum Brain Mapp., 2012), suggesting that such atypical visual recruitment also occurs during sensory processing in non-visual modalities. They are also in line with the general hypothesis of atypical sensorimotor building blocks as developmental precursors of sociocommunicative impairments in ASD.