Abstract: Methods for treating subjects afflicted with a psychiatric disorders [e.g., autism spectrum disorder (ASD), schizophrenia, and/or depression] are described herein. More particularly, the present invention relates to a method for treating a subject afflicted with or at risk for developing a psychiatric disorder (e.g., ASD, of which autism is a particular example) that calls for selecting a subject afflicted with or at risk for developing the psychiatric disorder based in part on previous in utero exposure to maternal immune activation (MIA) and treating the subject by administering pharmacological agents or implementing optogenetic tools or chemogenetic tools that correct dysregulated neuronal excitation/inhibition (E/I) ratios in cortical patches of the subject wherein the E/I ratio is dysregulated. A subject may also be selected for treatment using methods described herein based on the presence or detection of cortical patches having dysregulated neuronal E/I ratios.