Characterizing intracortical feedforward and feedback sensory processes in ASD

About This Grant

Project Summary Autism spectrum disorder (ASD) is a neurodevelopmental disorder long associated with functional connectivity abnormalities that are widespread throughout the brain. Despite countless studies on the topic, no single unifying model of functional connectivity abnormalities in ASD has emerged to date. Enthusiasm for studying functional connectivity differences in ASD has subsided in light of evidence of alterations that are more heterogeneous than some of the earlier hypotheses suggested, and because the links of these alterations to neural mechanisms of ASD have been challenging to map. Yet, one related theme that has garnered support has been that functional connectivity in ASD is increased in the bottom-up (or "feedforward") direction and decreased in the top-down (or "feedback) direction. Here, we propose to test a hypothesis that the functional characteristics of ASD are rooted in a fundamental imbalance between feedforward and feedback influences. This hypothesis stems from our preliminary data and prior studies, and it is motivated by many aspects of the ASD phenotype: These include increased perceived salience of sensory stimuli and evidence of reduced top-down control in ASD, which manifest across a range of atypical behaviors characteristic of the disorder. Thus far, mapping feedforward and feedback inputs non-invasively in the human brain has been methodologically challenging. Here we propose a multimodal neuroimaging approach, which combines (a) effective connectivity measures using millisecond temporal resolution magnetoencephalography (MEG) with (b) highly novel submillimeter-resolution layer- specific 7T functional MRI. We will use these advanced techniques to characterize feedforward and feedback flow of information along the auditory cortical hierarchy, in 90 ASD and 60 neurotypical (NT) adults, ages 21- 35, with average or above average IQ. Using our multimodal research design, which is firmly rooted in laminar neurophysiological recordings in non- human primates, we will pursue the following Specific Aims: (1) Test the hypothesis that feedforward inputs are abnormally increased in ASD relative to NT individuals; (2) Test the hypothesis that feedback inputs are abnormally decreased in ASD relative to NT individuals; (3) Test the hypothesis that the extent to which feedforward and feedback inputs in the ASD group are indeed different, is predictive of ASD severity and the extent of auditory processing deficits, assessed behaviorally. We expect that the results of this study will lead to a substantially more detailed, comprehensive, and mechanistically motivated framework for the wide range of functional connectivity abnormalities observed in ASD.