Objectives: The aim of the present study was to determine whether these abnormalities in change detection could also be evidenced in the visual modality. This fMRI study was thus designed to localize the brain activations elicited by visual unattended changing stimuli in adults with ASD compared to controls.
Methods: Seventeen healthy adults and twelve patients with ASD participated in the experiment. A passive oddball paradigm in which stimuli consisted in the deformation of a circle into an ellipse either in the horizontal (standard) or in the vertical direction (deviant, p=0.15) or into another shape (novel, p=0.15) was used. In order to present the visual stimuli outside the focus of attention, a concurrent task was required in which subjects had to stare at the fixation cross and to respond to its disappearance.
Results: Combined results from all volunteers highlight the involvement of both occipital (BA 18/19) and frontal (BA 6/8) regions in visual change detection. However adults with ASD display stronger activity in the bilateral occipital cortex (BA 18/19) and in the anterior cingulate cortex ACC (BA 32) associated with smaller activation in frontal regions (BA6/8) than controls. To further investigate ACC involvement during automatic change detection, a psychophysiological interaction analysis was performed with ACC as seed. Results show that the ACC is more functionally connected to sensory regions in ASD than in controls, but less connected to prefrontal and orbito-frontal cortices.
Conclusions: To conclude the present work evidenced atypical brain correlates of automatic visual change detection in adults with ASD. Indeed, compared to controls, larger sensory activation associated with reduced frontal activation were highlight in ASD. Besides, atypical psychophysiological interactions between frontal and occipital regions were evidenced, congruent with the idea of atypical connectivity between these regions described in the literature. Moreover, the atypical involvement of the anterior cingulate cortex in visual change detection can be related to previous results obtained in the auditory modality, thus suggesting that abnormalities in change detection are independent of the sensory modality. This supports the hypothesis of an altered general mechanism of change detection in patients with ASD that would underlie their unusual reaction to change.
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