Dr. James Lyons-Weiler, PhD, read over 3000 studies on autism and wrote a book to tell the tale:
"What I found were studies that clearly showed that neurotoxins such as aluminum, (read this before you claim aluminum is not a neurotoxin), mercury, valproaic acid, thalidomide, and other toxins are picked up by macrophages, deposited in the brain, and interfere with astrocytic glutamate uptake.
The excess glutamate prevents microglial cells from de-activating, once activated, and the microglia consume dendrites and neural precursor cells.
The autistic brain becomes uni-polar, with many one:one axon:dendrite connections. The microglia in their activated form are not available to shepherd multiple axon:dendrite connections during reinforcement learning, and thus the structures for inhibition feedback are missing. The autistic brain allows perceptual signals to get into the brain too far, too fast, and this is why there are perception sensitivities to light, and sounds.