Abstract
Individuals with high-functioning autism sometimes exhibit intact or superior performance on visuospatial tasks, in contrast to impaired functioning in other domains such as language comprehension, executive tasks, and social functions. The goal of the current study was to investigate the neural bases of preserved visuospatial processing in high-functioning autism from the perspective of the cortical underconnectivity theory. We used a combination of behavioral, functional magnetic resonance imaging, functional connectivity, and corpus callosum morphometric methodological tools. Thirteen participants with high-functioning autism and 13 controls (age-, IQ-, and gender-matched) were scanned while performing an Embedded Figures Task. Despite the ability of the autism group to attain behavioral performance comparable to the control group, the brain imaging results revealed several group differences consistent with the cortical underconnectivity account of autism. First, relative to controls, the autism group showed less activation in the left dorsolateral prefrontal and inferior parietal areas and more activation in visuospatial (bilateral superior parietal extending to inferior parietal and right occipital) areas. Second, the autism group demonstrated lower functional connectivity between higher-order working memory/executive areas and visuospatial regions (between frontal and parietal-occipital). Third, the size of the corpus callosum (an index of anatomical connectivity) was positively correlated with frontal-posterior (parietal and occipital) functional connectivity in the autism group. Thus, even in the visuospatial domain, where preserved performance among people with autism is observed, the neuroimaging signatures of cortical underconnectivity persist.
Highlights
Individuals with high-functioning autism sometimes exhibit intact or superior performance on visuospatial tasks, in contrast to impaired functioning in other domains such as language comprehension, executive tasks, and social functions
The underconnectivity account is based on findings of both functional underconnectivity and associated structural connectivity differences in individuals with autism, and has been supported by a growing number of neuroimaging studies across different domains (Just et al, 2004, 2007; Kana et al, 2006, 2007; Keller et al, 2007; Koshino et al, 2005, 2008; Mason et al, 2008)
It is possible that processing an entire complex figure may require participation of frontal regions that may not be necessary or useful for performing the Embedded Figures Task (EFT), whereas processing the simpler components of the figure may rely more on occipital and parietal areas
Summary
Individuals with high-functioning autism sometimes exhibit intact or superior performance on visuospatial tasks, in contrast to impaired functioning in other domains such as language comprehension, executive tasks, and social functions. The autism group demonstrated lower functional connectivity between higher-order working memory/executive areas and visuospatial regions (between frontal and parietal-occipital). Shah and Frith (1983) demonstrated that children with high-functioning autism exhibited superior performance relative to IQ- and age-matched controls on the Embedded Figures Task (EFT), in which individuals are asked to locate a simple figure that is embedded in a more complex configuration. A recently proposed theoretical account of autism, the cortical underconnectivity theory (Just et al, 2004; 2007), provides a neurobiological explanation of the psychological processes underlying the disorder This theory posits that autism is a neural systems disorder marked by inefficient interregional brain connectivity between frontal and posterior areas resulting in a deficit in integration of information at both psychological and neural levels. On the basis of the underconnectivity theory, we hypothesized that poorer access to frontal regions (or poorer frontal-posterior coordination) would not handicap people with autism in the EFT
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