Functional MRI Demonstrates Neural Suppression in Autism

A new functional magnetic resonance imaging (fMRI) study suggests that people with autism spectrum disorder (ASD) have weaker neural suppression in the visual cortex.

Researchers at the University of Minnesota (UMN; Minneapolis, USA), the University of Washington (UW; Seattle, USA), and other institutions used behavioral and fMRI tasks in 28 people with ASD, which showed they have an enhanced perception of large moving stimuli, as compared to 35 neuro-typical individuals. The brain responses in the early visual cortex (EVC) and the human middle temporal complex (hMT+), showed less neural suppression, but concomitant magnetic resonance spectroscopy (MRS) showed no differences among groups in neurotransmitter signals.

The researchers developed a computational model that could explain their observations, as well as some divergent previous findings. The model incorporates divisive normalization, as well as narrower top-down gain, which could result, for example, from a narrower window of attention. Thus, weaker neural suppression that is reflected in visual task performance and fMRI measures in ASD may also be attributable to differences in top-down processing. The study was published on May 29, 2020, in Nature Communications.

“Our work suggests that there may be differences in how people with ASD focus their attention on objects in the visual world that could explain the difference in neural responses we are seeing, and may be linked to symptoms like sensory hypersensitivity,” said lead author Michael-Paul Schallmo, PhD, of the UMN department of psychiatry. “Narrower top-down neural gain could, for example, reflect intrinsic differences in spatial attention; individuals with autism may have narrower windows of attention compared to neuro-typical individuals.”

ASD affects six per 1,000 children, and occurs more often among boys than girls. ASD affect three different areas of a child's life - social interaction, communication (both verbal and non-verbal), and behaviors and interests. The three main types are Asperger's syndrome, pervasive developmental disorder, not otherwise specified (PDD-NOS), and autistic disorder. The DSM -5 also included two rare but severe autistic-like conditions, called Rett syndrome and childhood disintegrative disorder.

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