1. Genetic–parents may pass onto their children the genetic make-up for hyperactivity. This theory gains support from the higher incidence of hyperactivity between hyperactive children and their families, particularly their fathers.
Not all hyperactive parents, however, have hyperactive children. Nor do all hyperactive children have hyperactive parents. One hypothesis is that some parents pass onto their children a vulnerability to hyperactivity, much the same way that parents pass onto their children a vulnerability to schizophrenia. Whether or not this vulnerability is activated depends on what happens to the child after he is born.
2. Brain or central nervous system dysfunction–hyperactive children may have a biochemical imbalance which in some way connects to their arousal levels. The most promising theory is that hyperactive children have under aroused nervous systems, related to a deficiency of certain chemicals in their brain. Hyperactive children’s natural tendency is to compensate for this deficiency through their hyperactive behavior. Stimulant medication reduces the need for these children to behave hyperactively, because it closely resembles the chemicals hyperactive children do not have enough of.
3. Developmental lag–hyperactivity may not be a disorder at all, but rather some children’s slower-than-normal rate of maturing. This means that hyperactive children, as they grow older, have the potential of catching up to their peers. Although this may be true for some of hyperactive children’s symptoms, poor adaptability and a lack of coordination for example, it is generally not true for their more significant behaviors.
4. Sex-linked hormones–because hyperactive boys outnumber girls by a six to one margin, it is thought that hyperactive children have unusually high amounts of male hormones in their bodies, possibly giving them less stable nervous systems.
5. Food additives–children’s hyperactivity may be triggered by food additives such as artificial colors and flavors, preservatives, and the flavor enhancer MSG. This theory was popularized by Dr. B. Feingold, who devised an additive-free diet.
Did the diet work? According to Dr. Feingold it did for up to 50 per cent of his cases. However, controlled studies conducted later on yielded more modest results. An important variable contributing to Feingold’s elevated success rates seemed to be parents’ expectations for success, not the diet itself. It is now thought that only a small number of hyperactive children, perhaps less than five per cent, and mostly those in preschool, benefit from the diet.