Abstract
BackgroundThe insular cortex comprises multiple functionally differentiated sub-regions, each of which has different patterns of connectivity with other brain regions. Such diverse connectivity patterns are thought to underlie a wide range of insular functions, including cognitive, affective, and sensorimotor processing, many of which are abnormal in autism spectrum disorder (ASD). Although past neuroimaging studies of ASD have shown structural and functional abnormalities in the insula, possible alterations in the sub-regional organization of the insula and the functional characteristics of each sub-region have not been examined in the ASD brain.MethodsResting-state functional magnetic resonance imaging (rs-fMRI) data were acquired from 36 adult males with ASD and 38 matched typically developed (TD) controls. A data-driven clustering analysis was applied to rs-fMRI data of voxels in the left and right insula to automatically group voxels with similar intrinsic connectivity pattern into a cluster. After determining the optimal number of clusters based on information theoretic measures of variation of information and mutual information, functional parcellation patterns in both the left and the right insula were compared between the TD and ASD groups. Furthermore, functional profiles of each sub-region were meta-analytically decoded using Neurosynth and were compared between the groups.ResultsWe observed notable alterations in the anterior sector of the left insula and the middle ventral sub-region of the right insula in the ASD brain. Meta-analytic decoding revealed that whereas the anterior sector of the left insula contained two functionally differentiated sub-regions for cognitive, sensorimotor, and emotional/affective functions in TD brain, only a single functional cluster for cognitive and sensorimotor functions was identified in the anterior sector in the ASD brain. In the right insula, the middle ventral sub-region, which is primarily specialized for sensory- and auditory-related functions, showed a significant volumetric increase in the ASD brain compared with the TD brain.ConclusionsThe results indicate an altered organization of sub-regions in specific parts of the left and right insula of the ASD brain. The alterations in the left and right insula may constitute neural substrates underlying abnormalities in emotional/affective and sensory functions in ASD.Electronic supplementary materialThe online version of this article (doi:10.1186/s13229-016-0106-8) contains supplementary material, which is available to authorized users.
Highlights
The insular cortex comprises multiple functionally differentiated sub-regions, each of which has different patterns of connectivity with other brain regions
The results indicate an altered organization of sub-regions in specific parts of the left and right insula of the autism spectrum disorder (ASD) brain
variation of information (VI) had local minima at k = 5 and 8 (VI: 0.167 ± 0.0031 [mean ± standard errors of the mean (SEM)] for k = 5 and VI: 0.151 ± 0.0026 for k = 8), while mutual information (MI) had a local maximum at k = 8 (MI: 0.740 ± 0.0046) (Fig. 2a)
Summary
The insular cortex comprises multiple functionally differentiated sub-regions, each of which has different patterns of connectivity with other brain regions. Previous resting-state fMRI studies of adolescent and adult ASD have shown reduced functional connectivity (FC) of the anterior, middle, and posterior insula with distant brain regions, including the amygdala and the somatosensory cortex [6,7,8]. Convergent evidence from these structural, functional, and FC studies strongly prompts more detailed investigations of the insula to advance our understanding of the neural substrates of ASD
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