18731
Thalamo-Cortical Underconnectivity during Sensory Stimulation in Youth with ASD
Children with autism spectrum disorders (ASD) often exhibit sensory over-responsivity (SOR), which may cause them to react negatively to sensory stimuli such as noisy environments or scratchy clothing (Liss et al., 2006). Rates of SOR are over five times higher in children with ASD than in typically developing (TD) children (e.g., Baranek et al., 2006; Ben-Sasson et al., 2007) and SOR is associated with increased functional impairment (e.g., Liss et al., 2006; Pfeiffer et al., 2005). Previously, we found that individuals with ASD and SOR have hyperactivation in the amygdala and sensory cortices in response to mildly aversive sensory stimuli. Further, SOR was related to decreased neural habituation in these areas (Green et al., 2014; Green et al., under review). The present study extends these findings by examining thalamo-cortical connectivity in response to tactile and auditory stimuli in youth with and without ASD. The thalamus is considered the “hub” of the brain’s sensory systems, and furthermore there is evidence for reduced thalamo-cortical structural connectivity in individuals with Sensory Processing Disorder (Owen et al., 2013). We focused on the pulvinar specifically because this thalamic nucleus is thought to aid in interpretation and integration of sensory information (e.g., Sherman & Guillery, 1996).
Objectives: To compare functional connectivity within the brain’s sensory networks in youth with and without ASD during exposure to sensory stimuli.
Methods: Participants were 19 children and adolescents with ASD and 19 TD matched controls, between 9-17 years of age. During fMRI, participants were presented with mildly aversive auditory stimuli (noisy traffic sounds) and tactile stimuli (scratchy sweater rubbed from wrist to elbow). The block design paradigm included 4, 15-sec trials of each stimulus type: the auditory stimulus, tactile stimulus, or both. A psychophysiological interaction (PPI) analysis was conducted to examine functional connectivity during exposure to both sensory stimuli with the pulvinar area of the thalamus as a seed region. The pulvinar seed was functionally defined by first masking a 5mm sphere around the peak coordinate of activation in each group during the Joint condition and then adding the two masks. Within- and between-group-level analysis were thresholded at Z > 1.7 and corrected for multiple comparisons at p < .05. Both positive and negative connectivity were examined.
Results: Results are illustrated in figure below. The TD group demonstrated widespread task-based thalamo-cortical connectivity, including negative connectivity between pulvinar and primary and secondary somatosensory cortex, as well as positive connectivity between pulvinar and additional frontal and temporal cortical regions. In contrast, the ASD group had no significant task-based thalamo-cortical connectivity. Furthermore, a small volume analysis focused on the amygdala demonstrated that the ASD, but not TD group showed positive connectivity between pulvinar and amygdala.
Conclusions: In one of the first fMRI studies of sensory over-responsivity in children with ASD, we show task-related underconnectivity in ASD. Results suggest decreased cortical-thalamic inhibition, and an exaggeration of stimulus salience in ASD. These findings could help explain sensory integration deficits in ASD as well as reduced somatosensory cortical habituation to tactile stimuli.