Autism Spectrum Disorders (ASD) are an etiologically and clinically heterogeneous group of neurodevelopmental disorders. The pathophysiology of ASD remains largely unknown. One essential and well-documented observation is high comorbidity between ASD and epilepsy. Electroencephalography (EEG) is the most widely used tool to detect epileptic brain activity. The EEG signal is characterized by a high temporal resolution (on the order of milliseconds) allowing for precise temporal examination of cortical activity. This review addresses the main EEG findings derived from both the standard or qualitative (visually inspected) EEG and the quantitative (computer analyzed) EEG during resting state in individuals with ASD. The bulk of the evidence supports significant connectivity disturbances in ASD that are possibly widespread with two specific aspects: over-connectivity in the local networks and under-connectivity in the long-distance networks. Furthermore, the review suggested that disruptions appear more severe in later developing parts of the brain (e.g., prefrontal cortex). Based on available information, from both the qualitative and quantitative EEG literature, we postulate a preliminary hypothesis that increased cortical excitability may contribute to the significant overlap between ASD and epilepsy and may be contributing to the connectivity deviations noted. As the presence of a focal epileptic discharge is a clear indication of such hyperexcitability, we conclude that the presence of epileptic discharges is a potential biomarker at least for a subgroup of ASD
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