A Magnetic Resonance Spectroscopy Study of Superior Visual Search Abilities in Children with Autism Spectrum Disorder

Abstract

Although diagnosed on the basis of deficits in social communication and interaction, autism spectrum disorder (ASD) is also characterized by superior performance on a variety of visuospatial tasks, including visual search. In neurotypical individuals, region-specific concentrations of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) are associated with individual differences in attention and perception. While it has been hypothesized that ASD may be associated with an excitatory-inhibitory imbalance, it remains unclear how this may contribute to accelerated visual search performance in individuals with ASD. To investigate this, 21 children with ASD and 20 typically developing children participated in a visual search task and a magnetic resonance spectroscopy study to detect neurochemical concentrations, including GABA. Region-specific neurochemicals were examined in the right frontal eye fields, right temporal-parietal junction (rTPJ), and bilateral visual cortex (VIS). GABA concentrations did not differ between groups; however, in children with ASD, greater GABA concentration in the VIS was related to more efficient search. Additionally, lower VIS GABA levels were also associated with increased social impairment. Finally, we found reduced N-acetyl aspartate, total creatine, glutamate and glutamine (Glx), GABA/Glx in the rTPJ, suggestive of neuronal dysfunction in a critical network hub. Our results show that GABA concentrations in the VIS are related to efficient search in ASD, thus providing further evidence of enhanced discrimination in ASD. Autism Res 2020, 13: 550-562. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Children with autism spectrum disorder (ASD) often perform better than their non-ASD peers on visual search tasks; however, it is unclear how they achieve this superior performance. Using magnetic resonance spectroscopy to measure neurochemicals in the brain, we found that the level of one, gamma-aminobutyric acid, in the visual cortex was directly related to search abilities in children with ASD. These results suggest that faster search may relate to enhanced perceptual functioning in children with ASD.

Keywords: autism spectrum disorder; frontal eye field; gamma-aminobutyric acid; magnetic resonance spectroscopy; temporal-parietal junction; visual cortex; visual search.

Figure 1.. Example of visual search task (VST) for target present

(left) and target absent (right) conditions (set size 36).

Figure 2.. Volumes of Interest (VOI) for Magnetic Resonance Spectroscopy (MRS) Acquisition.

A) Representative locations and the % overlap for repeatability of voxel placement in volumes of interest (VOIs): right frontal eye fields (rFEF, 78.8% overlap), right temporal-parietal junction (rTPJ, 84% overlap), and visual cortex (VIS, 82.3% overlap). Shown in radiological orientation. B) Mean (standard deviation in grey) VIS difference spectrum acquired using MEGA-semi-LASER (MEGA-sLASER) with a TE of 68ms, TR of 2000ms, and 128 averages. C) Mean rTPJ ¹H spectrum acquired using semi-LASER (sLASER) with an echo time (TE) of 35ms, repetition time (TR) of 2000ms, and 64 averages.

Figure 3. Visual Search Task Performance.

A) Accuracy is shown for target absent and target present conditions in the VST across set sizes of 18, 24, and 36. B) Reaction time (RT) for the target absent and target present conditions are shown

Figure 4.. Box plots of metabolite concentrations for ASD and TD children.

Distributions for neurochemicals in all three regions (rFEF, rTPJ, and VIS) are shown in A) GABA+, B) NAA, C) Glx, and D) tCr. Post-hoc analysis showed there were significant differences in NAA, Glx, and tCr between ASD and TD in the TPJ. * indicates statistical significance where p < 0.05.

Figure 5.. Correlations between GABA and VST performance and ASD symptomatology in the visual cortex (VIS).

A) Scatterplot of VIS VOI GABA+ values and RT x set size slope for the absent condition. B) Scatterplot of VIS VOI GABA+ values and Social Responsiveness Scale (SRS) Social Communication Index (SCI).