A Multimodal Investigation of Inhibitory Dysfunction in Autism Spectrum Disorder



 DESCRIPTION (provided by applicant): It is thought that impairments in the main inhibitory neurotransmitter GABA underlie Autism, at least to some degree. Children with Autism often show abnormal touch processing as well as abnormal motor control, which have a large impact on social interactions and quality of life. GABA plays an important role in the regulation of both tactile and motor processing and it is possible that such symptoms are driven by impaired GABAergic function. However, it remains unclear how cortical dysfunction leads to behavioral dysfunction and how different GABAergic processes contribute to behavioral abnormalities. It has become possible to measure tactile sensitivity objectively using psychophysics, and we developed tasks that are based on invasive studies of sensory function, and can be linked to GABAA and GABABergic mechanisms. Recently we have shown impaired tactile sensitivity in children with Autism, showing poor amplitude discrimination (GABAA) and detection threshold (GABAB), and we showed reduced GABA levels using Magnetic Resonance Spectroscopy. However, a direct connection between specific GABAergic mechanisms and behavior has not yet been shown. It is possible to directly test GABAA and GABAB-ergic mechanisms using peripheral and transcranial magnetic stimulation (TMS) methods as has been shown by pharmacological studies. Applying these non-invasive stimulation methods will form the training portion of this application. The overall goal of this grant is to investigate specific inhibitory mechanisms in SM1 in children with ASD and their relation to sensory behavior. Using a multimodal non-invasive approach, we aim to test whether different GABAergic mechanisms are indeed impaired in children with Autism, whether these are linked to sensorimotor behavior and symptom severity, and how these relate to cortical GABA levels. We hypothesize that behavioral tasks and brain stimulation protocols that utilize inhibition will be impaired in childrn with ASD, and that performance that performances between conditions that probe the same GABAergic mechanisms (GABAA (e.g. amplitude discrimination and TMS measuring short-interval cortical inhibition) or GABAB (e.g. detection thresholds and TMS measuring long-interval cortical inhibition) are associated. A better understanding of the role of GABAergic dysfunction in autism may allow for the development of specific therapies that can alleviate the symptoms and improve quality of life.