Doctors know a lot about ADHD, but they are not completely certain what causes it. The current view is that the syndrome has underlying biological-neurological origins (possibly with a genetic, or inherited, component) that interact with the individual’s environment to result in the manifestation of ADHD.Previous hypotheses regarding the causes, or etiologies, of ADHD have focused on brain damage caused during pregnancy or birth; other causes of brain damage early in life, such as trauma or infections; troubled family environments; inadequate parenting; food additives; sugar in the diet; and malnutrition. It is now clear that no one of these etiologies is universally present. The question of food additives and sugar has been carefully examined in controlled studies and has been convincingly ruled out as an etiology. While some people with ADHD have undergone prenatal fetal distress or birth trauma, and while some, upon examination, show signs suggestive of brain dysfunction, others may have no such history and may have a completely normal physical examination.One of the problems with researching the possible biological causes of ADHD is the difficulty in defining just what brain functions are disturbed. Researchers have attempted to break down the function of attention into its components, which can then be studied and even localized to specific parts of the brain. For example, Dr. Alan Mirsky of the NIMH has divided attention into the following three components:1. the capacity to select a part of the environment to focus on, the ability to sustain that focus over time, andthe ability to change or shift focus, i.e., to stop focusing on one part of the environment and start focusing on another part of the environment.With the advent of positron emission tomography (PET), researchers are now trying to localize brain function while it is occurring. For example, in one study adult subjects were asked to learn a list of words while a PET scanner analyzed how much glucose different parts of their brain used while they worked. In people with ADHD, the brain areas involved in attention used less glucose than in normal control subjects.Another area of research involves the dramatic results achieved in improving some ADHD symptoms through the use of the stimulants methylphenidate (Ritalin) and dextroamphetamine (Dexedrine). Studies have shown that these stimulants increase the amount of dopaminergic neurotransmitters, the chemicals that carry electrical messages from one nerve cell to the next, available in the central nervous system. Stimulants may also increase the amount of another transmitter, norepinephrine, in the parts of the brain related to activation and arousal. However, the impact of these stimulants is very complex, and it does not follow that ADHD is caused by a simple deficiency in the quantity of these transmitters. What is very likely is that the underlying biological disorders somehow cause a disturbance in neurotransmitter functions. Research in this area will hopefully continue to enhance our knowledge of both the etiology and management of ADHD.From the moment of conception, the environment has an impact on the fetus. Obviously poor nutrition, absence of adequate prenatal care, metabolic and toxic factors (such as alcohol, cigarette, or drug use by the pregnant mother), infections, stress, birth trauma, premature delivery, and low birth weight can all affect the health of the newborn infant. In fact, studies have shown a correlation between these factors and later ADHD.Environmental influences become ever more complex as an individual proceeds through development after birth. While there are no firm correlations between ADHD and family and parenting variables, it is clear that from the beginning of life, the environment of these youngsters interacts in complex ways to bring about the complicated symptom picture that we call ADHD. This interplay between biology and environment will be enlarged upon in the next chapter’s discussion of ADHD at different developmental stages.For now it is clear that many different variables, including genetic, biological, and psychosocial factors, combine and interact to form the syndrome known as ADHD.*8\173\2*