UC San Diego

Rationale : The present dissertation project specifically sought to understand brain networks connecting with the thalamus, an important subcortical relay structure through which almost all sensory information is routed. In view of the known fundamental importance of thalamocortical connectivity for the development of regional functional specialization in cerebral cortex, it is surprising how little firm knowledge is available about the thalamus and its connections with cortex in Autism Spectrum Disorders (ASD). Therefore, it is crucial to examine the role of the thalamus in regulating these functions for an improved understanding of neurodevelopmental mechanisms associated with ASD. Design : The first study of this project examined functional and anatomical connectivity between five broad cortical regions of interests (ROIs; e.g., temporal lobes) and the thalamus for a sample of children and adolescents with ASD (N=26) compared to TD controls (N=27). This first study allowed us to broadly characterize the connectivity between ipsilateral thalamus and the different lobes. In the second study, we delved deeper into the specificity of connections between more narrowly specialized regions (e.g., fusiform gyrus or anterior temporal pole) and the thalamus for a larger sample of children and adolescents with ASD (N=37) compared to TD controls (N=38). Results : In the first study, we found evidence of both anatomical and functional underconnectivity between the prefrontal, parietal- occipital, motor, and somatosensory cortices with ipsilateral thalamus. The only exception was functional connectivity with the temporal lobe, which was increased in the ASD group, especially in the right hemisphere. Delving deeper into the specificity of these connections in the second study, we found that functional connectivity was atypically reduced in the ASD group for supramodal association cortices involved in higher-order cognition (e.g., language, face processing), but was increased for sensorimotor and limbic regions (e.g., auditory cortex). Discussions : Our findings provide evidence of regionally specific aberrations of thalamic connectivity in frontal and temporal lobes, with additional involvement of some parieto-occipital ROIs. These findings could be related to early maturation of limbic and sensorimotor regions in the context of early overgrowth in ASD, at the expense of thalamocortical connectivity with later maturing cortical regions