Extensive MRI evidence indicates early brain overgrowth in autism spectrum disorders (ASDs). Local gyrification may reflect the distribution and timing of aberrant cortical expansion in ASDs. We examined MRI data from (Study 1) 64 individuals with ASD and 64 typically developing (TD) controls (7-19 years), and from (Study 2) an independent sample from the Autism Brain Imaging Data Exchange (n = 31/group). Local Gyrification Index (lGI), cortical thickness (CT), and surface area (SA) were measured. In Study 1, differences in lGI (ASD > TD) were found in left parietal and temporal and right frontal and temporal regions. lGI decreased bilaterally with age, but more steeply in ASD in left precentral, right lateral occipital, and middle frontal clusters. CT differed between groups in right perisylvian cortex (TD > ASD), but no differences were found for SA. Partial correlations between lGI and CT were generally negative, but associations were weaker in ASD in several clusters. Study 2 results were consistent, though less extensive. Altered gyrification may reflect unique information about the trajectory of cortical development in ASDs. While early overgrowth tends to be undetectable in later childhood in ASDs, findings may indicate that a trace of this developmental abnormality could remain in a disorder-specific pattern of gyrification.

Auditory signals (A) are perceived as lasting longer than visual signals (V) of the same physical duration when they are compared together. Despite considerable debate about how this illusion arises psychologically, the neural underpinnings have not been studied. We used functional magnetic resonance imaging (fMRI) to investigate the neural bases of audiovisual temporal distortions and more generally, intersensory timing. Adults underwent fMRI while judging the relative duration of successively presented standard interval–comparison interval (CI) pairs, which were unimodal (A–A, V–V) or crossmodal (V–A, A–V). Mechanisms of time dilation and compression were identified by comparing the two crossmodal pairs. Mechanisms of intersensory timing were identified by comparing the unimodal and crossmodal conditions. The behavioral results showed that auditory CIs were perceived as lasting longer than visual CIs. There were three novel fMRI results. First, time dilation and compression were distinguished by differential activation of higher-sensory areas (superior temporal, posterior insula, middle occipital), which typically showed stronger effective connectivity when time was dilated (V–A). Second, when time was compressed (A–V) activation was greater in frontal cognitive-control centers, which guide decision making. These areas did not exhibit effective connectivity. Third, intrasensory timing was distinguished from intersensory timing partly by decreased striatal and increased superior parietal activation. These regions showed stronger connectivity with visual, memory, and cognitive-control centers during intersensory timing. Altogether, the results indicate that time dilation and compression arise from the connectivity strength of higher-sensory systems with other areas. Conversely, more extensive network interactions are needed with core timing (striatum) and attention (superior parietal) centers to integrate time codes for intersensory signals.

No abstract

Although a growing literature highlights sex differences in autism spectrum disorder clinical presentation, less is known about female variants at the neural level. We investigated sex-related patterns of functional connectivity within and between functional networks in children and adolescents with autism spectrum disorders, compared to typically developing peers. Resting-state functional magnetic resonance imaging data for 141 children and adolescents (7–17 years) selected from an in-house sample and four sites contributing to the Autism Brain Imaging Database Exchange (ABIDE I and II) were submitted to group independent component analysis to generate resting-state functional networks. Functional connectivity was estimated by generating resting-state functional network correlation matrices, which were directly compared between males and females, and autism spectrum disorder and typically developing groups. Results revealed greater connectivity within the default mode network in typically developing girls as compared to typically developing boys, while no such sex effect was observed in the autism spectrum disorder group. Correlational analyses with clinical indices revealed a negative relationship between sensorimotor connectivity and history of early autism symptoms in girls, but not in boys with autism spectrum disorder. A lack of neurotypical sex differentiation in default mode network functional connectivity observed in boys and girls with autism spectrum disorder suggests that sex-related differences in network integration may be altered in autism spectrum disorder. Lay summary We investigated whether children and adolescents with autism spectrum disorders show sex-specific patterns of brain function (using functional magnetic resonance imaging) that are well documented in typically developing males and females. We found, unexpectedly, that boys and girls with autism do not differ in their brain functional connectivity, whereas typically developing boys and girls showed differences in a brain network involved in thinking about self and others (the default mode network). Results suggest that autism may be characterized by a lack of brain sex differentiation.