Autism Spectrum Disorder (ASD) is a complex developmental brain disorder characterised by impaired communication and repetitive behaviors, and is often accompanied by intellectual disability. According to the Public Health Agency of Canada, 1 in 66 children and youth in Canada is diagnosed with ASD. The personal and societal costs of treatment and caregiving are immense with lifetime financial costs of $1.2-4.7 million to care for “typical” individuals with ASD. Current therapeutic interventions for ASD are oriented toward symptom management but there is no treatment for the underlying disorder, as the cause of the disorder remains unknown. A greater understanding of the basis of ASD is imperative to develop the most effective diagnostic criteria and treatments. Neuroimaging studies have indicated that brain network dysfunction is an important feature of ASD. This proposal aims to investigate brain dysfunction associated with ASD in novel ways, using light-based methods for imaging and manipulating brain activity in animal models. These innovative techniques incorporate a scale of assessment, called mesoscale, which allows the assessment of brain activity at both a microscopic level and a brain-wide level at the same time. By furthering the understanding of the neuroimaging features of ASD, as well as how altered brain activity manifests in the symptoms of ASD, this research will inform the development of diagnostic criteria and treatments for ASD.