Genuine question: has there been any study that actually measured the &quot;levels&quot; of neurotransmitters in the brain and correlated them with the subjects&#x27; behavior? Has there been any study that actually demonstrates what the normal levels of these chemicals are in adults and children, and what the normal range is, and what environmental and nutritional factors can influence them? I ask because I constantly hear the &quot;chemical imbalance&quot; explanation for behavioural issues and prescribing these drugs, but I have not ever found a paper that actually provides scientific evidence for this explanation.