Functional brain organization for visual search in ASD

Abstract

Although previous studies have shown that individuals with autism spectrum disorder (ASD) excel at visual search, underlying neural mechanisms remain unknown. This study investigated the neurofunctional correlates of visual search in children with ASD and matched typically developing (TD) children, using an event-related functional magnetic resonance imaging design. We used a visual search paradigm, manipulating search difficulty by varying set size (6, 12, or 24 items), distractor composition (heterogeneous or homogeneous) and target presence to identify brain regions associated with efficient and inefficient search. While the ASD group did not evidence accelerated response time (RT) compared with the TD group, they did demonstrate increased search efficiency, as measured by RT by set size slopes. Activation patterns also showed differences between ASD group, which recruited a network including frontal, parietal, and occipital cortices, and the TD group, which showed less extensive activation mostly limited to occipito-temporal regions. Direct comparisons (for both homogeneous and heterogeneous search conditions) revealed greater activation in occipital and frontoparietal regions in ASD than in TD participants. These results suggest that search efficiency in ASD may be related to enhanced discrimination (reflected in occipital activation) and increased top-down modulation of visual attention (associated with frontoparietal activation).

Autism Spectrum Disorder: Does Neuroimaging Support the DSM-5 Proposal for a Symptom Dyad? A Systematic Review of Functional Magnetic Resonance Imaging and Diffusion Tensor Imaging Studies

“…On the other hand, syntacticsemantic deficits in ASD are much more related to decreased activity of the IFG and increased activity of Wernicke's area, to the use of visual pathways to support language comprehension, and to the presence of reduced or reversed leftward asymmetry. This 'visually-mediated' language processing coexists in these patients with abnormal visuomotor processing, showing a functional overlap between both cognitive processes, where the processing strategy depends to an abnormally large extent on activation of parieto-occipital pathways (Belmonte et al 2010;Belmonte and Yurgelun-Todd 2003;Bolte et al 2008;Damarla et al 2010;Keehn et al 2008;Ring et al 1999;Shukla et al 2010b). The distinction between the syntacticsemantic and semantic-pragmatic component of language has been supported by neuropsychological and neuroimaging studies.…”

Thinking in Pictures as a Cognitive Account of Autism

“…However, looking at a target/distracter search task, Keehn et al (2008) found increased activation in individuals on the autism spectrum compared to TD controls in both frontoparietal and occipital regions. This study also found that, while patterns of activation differed for controls between an easy feature search task and a more difficult one, no such differences were found for the autism group.…”

Update on autism: A review of 1300 reports published in 2008

“…A visual search test revealed greater activation in the visual cortex (also frontoparietal), likely related to enhanced discrimination and increased modulation of visual attention [252]. Finally, Bonilha et al [254] reported that patients with autism showed a decrease in white matter in the visual cortex (as well as the frontal, temporal, and parietal cortex) in association with a generally enlarged cortex.…”

“…The same type of hypoperfusion was found in the parents and also the siblings. Keehn et al [252] used event-related fMRI to visual stimuli to show greater activation in frontal (also parieto-occipital) regions in individuals with autism than in controls. The conclusion was that a search efficiency in autism may be related to increased modulation of visual attention.…”