The inflammation observed in the brain (neuroinflammation) and the resulting activated oxidative stress, along with the free radicals and reactive oxygen species (ROS) produced and increased in quantity in the brain, stimulate the immune system in the brain and cause the activation and increase in number of a series of cells (microglia cells) responsible for the brain’s immune system, leading to dysfunctions in their functions. In addition to their roles in the brain’s immune system (macrophage, phagocytosis), microglia cells have many important functions related to nerve cells, synapses, and signal transmission systems in the brain; primarily, neuron production (neurogenesis), synapse production (synaptogenesis), pruning of synapses, organization of synaptic structure, regulation of synaptic signal transmission systems, synaptic excitation and inhibition, and maintaining and sustaining the E/I balance. As a response to inflammation, disorders develop in the neuronal signal transmission systems of microglia cells, which excessively increase in number in the brain, leading to imbalances in their (E/I) functions. This, in turn, causes the emergence of various conditions, primarily the behavioral disorders observed in autism.