Out of curiosity, heavy metals can also induce excitability. Before people knew mercury was neurotoxic, it was inhaled as a health promoting mist giving coffee-like stimulation. Just makes me think if observed changes in brain composition is genetics, or are these kids being poisoned in some way.

Well I guess this doesn't fully cover ADHD, but it's not completely out of its scope either. However that's just one heavy-metal. There are so many more possibilities, including pesticides and herbicides or other neurologically active agents.

Short‐chained alkyl mercury and elemental mercury produce a constellation of neurological abnormalities collectively referred to as erethism. Erethism includes anxiety, irritability, mania, sleep disturbance, depression, and cognitive deficits. Visual disturbance, hearing loss, paresthesias, and tremor may also be present.