Neural Mechanisms Underlying Visuospatial Expertise in ASD

Background:  Visuospatial strengths have been well documented in a large proportion of individuals with autism spectrum disorders (ASD). Brain mechanisms underlying visuospatial abilities have been investigated in previous studies, revealing higher activation in occipito-parietal regions and diminished activation in some frontal regions in ASD (Kana et al., 2013; McGrath et al., 2012; Silk et al., 2006). However, no such studies have investigated the brain correlates underlying superior visuospatial abilities in distinct subgrouping of ASD individuals based on their visuospatial abilities.

Objectives:  The principal goal of this study was to uncover the neural network involved in visuospatial abilities and expertise in ASD in different subgrouping based on their Wechsler Block Design subtest’s performance using functional magnetic resonance imaging (fMRI) technique.

Methods: Forty ASD male participants, 20 of them having enhanced visuospatial skills (defined as relative strength on Block Design subtest) (Wechsler, 2008), and 20 non-ASD male participants (age 18-37) matched on age and IQ will perform two visuospatial tasks in the fMRI scanner. The first task is an adaptation of the original Block Design subtest (BD) suitable for presentation in the MRI scanner. Perceptual cohesiveness of the target design is parametrically varied across the 90 trials. The second task is a classic mental rotation (MR) task with three-dimensional shapes. 104 pairs of images were presented with four different spatial orientations (0, 70, 140 and 180 degrees). Both tasks are presented in an event-related design, with percentage of correct responses and response time recorded. Preliminary results include 23 ASD participants, 10 of them having enhanced visuospatial skills, and 16 non-ASD subjects.

Results: Despite no differences in accuracy and response time across the three groups, ASD participants displayed greater activity in anterior prefrontal cortex (PFC) in both tasks compared to non-ASD participants. Furthermore, the MR task revealed higher activation in superior and inferior frontal gyri, superior parietal lobule and cerebellum in ASD participants compared to non-ASD participants, whereas the adapted BD subtest revealed higher activation in the right superior and middle temporal gyri and the left anterior cingulate gyrus in ASD participants. Non-ASD participants showed higher activation in supplementary motor area, and in primary motor and sensory areas in the MR task. Further analyses compared the brain correlates of ASD with and without superior visuospatial abilities. Higher activation in bilateral ventrolateral PFC was observed in the ASD group without superior visuospatial abilities while performing the adapted BD task, whereas higher activation in some occipital, parietal and temporal regions was observed for the ASD group with superior visuospatial abilities during the MR task.

Conclusions: Our preliminary results are inconsistent with previous results showing lesser activation in some frontal regions in ASD while processing visuospatial information (McGrath et al., 2012). Furthermore, despite equivalent performance, increased parietal and occipital activity in ASD individuals with superior visuospatial abilities compared to those without may suggest enhanced functional resource allocation in regions dedicated to visuospatial processing and expertise. Diminished prefrontal activity in ASD individuals with superior visuospatial abilities may suggest more efficient visuospatial processing requiring less cognitive control resources.