Abstract
Abnormal sensory processing has been observed in autism, including superior visual motion discrimination, but the neural basis for these sensory changes remains unknown. Leveraging well-characterized suppressive neural circuits in the visual system, we used behavioral and fMRI tasks to demonstrate a significant reduction in neural suppression in young adults with autism spectrum disorder (ASD) compared to neurotypical controls. MR spectroscopy measurements revealed no group differences in neurotransmitter signals. We show how a computational model that incorporates divisive normalization, as well as narrower top-down gain (that could result, for example, from a narrower window of attention), can explain our observations and divergent previous findings. Thus, weaker neural suppression is reflected in visual task performance and fMRI measures in ASD, and may be attributable to differences in top-down processing.
Highlights
Abnormal sensory processing has been observed in autism, including superior visual motion discrimination, but the neural basis for these sensory changes remains unknown
We present a computational account of weaker spatial suppression in autism spectrum disorder (ASD) in the context of a divisive normalization model
98% 3% Contrast stronger for high- vs. low-contrast stimuli, but there was no significant interaction between group and contrast. These results indicate that functional magnetic resonance imaging (fMRI) responses within early visual cortex (EVC) reflect spatial suppression, but unlike for motion discrimination or responses in hMT+, there was no difference in fMRI suppression within EVC between participants with ASD and NTs
Summary
Abnormal sensory processing has been observed in autism, including superior visual motion discrimination, but the neural basis for these sensory changes remains unknown. Large enhancements in visual motion discrimination performance found in ASD compared to neurotypical (NT) controls[4] were recently described as a deficit in normalization2—a computation that reflects neural processes which regulate (i.e., suppress) neural responses in the brain[10,11] Under this hypothesis, weaker normalization in ASD would result in larger amplitude neural responses and lead to enhanced behavioral performance in tasks that depend on neural sensitivity, such as motion discrimination. Using this model we show how variability in the width of top–down gain across individuals with ASD (while always remaining smaller than NTs), as well as interactions with stimulus size and contrast, can potentially account for discrepant findings of both enhanced and impaired sensory processing in this disorder
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