Excerpted from the National Institute of Mental Health (NIMH) Publication Attention Deficit Hyperactivity Disorder (ADHD), 2012.
What is Attention Deficit Hyperactivity Disorder?
Attention deficit hyperactivity disorder (ADHD) is one of the most common childhood brain disorders and can continue through adolescence and adulthood. Symptoms include difficulty staying focused and paying attention, difficulty controlling behavior, and hyperactivity (over-activity). These symptoms can make it difficult for a child with ADHD to succeed in school, get along with other children or adults, or finish tasks at home.
Brain imaging studies have revealed that, in youth with ADHD, the brain matures in a normal pattern but is delayed, on average, by about three years. The delay is most pronounced in brain regions involved in thinking, paying attention, and planning. More recent studies have found that the outermost layer of the brain, the cortex, shows delayed maturation overall, and a brain structure important for proper communications between the two halves of the brain shows an abnormal growth pattern. These delays and abnormalities may underlie the hallmark symptoms of ADHD and help to explain how the disorder may develop.
Treatments can relieve many symptoms of ADHD, but there is currently no cure for the disorder. With treatment, most people with ADHD can be successful in school and lead productive lives. Researchers are developing more effective treatments and interventions, and using new tools such as brain imaging, to better understand ADHD and to find more effective ways to treat and prevent it.
What are the symptoms of ADHD in children?
Inattention, hyperactivity, and impulsivity are the key behaviors of ADHD. It is normal for all children to be inattentive, hyperactive, or impulsive sometimes, but for children with ADHD, these behaviors are more severe and occur more often. To be diagnosed with the disorder, a child must have symptoms for six or more months and to a degree that is greater than other children of the same age.
Children who have symptoms of inattention may:
• Be easily distracted, miss details, forget things, and frequently switch from one activity to another
• Have difficulty focusing on one thing
• Become bored with a task after only a few minutes, unless they are doing something enjoyable
• Have difficulty focusing attention on organizing and completing a task or learning something new
• Have trouble completing or turning in homework assignments, often losing things (e.g., pencils, toys, assignments) needed to complete tasks or activities
• not seem to listen when spoken to
• Daydream, become easily confused, and move slowly
• Have difficulty processing information as quickly and accurately as others
• Struggle to follow instructions.
Children who have symptoms of hyperactivity may:
• Fidget and squirm in their seats
• Talk nonstop
• Dash around, touching or playing with anything and everything in sight
• Have trouble sitting still during dinner, school, and story time
• Be constantly in motion
• Have difficulty doing quiet tasks or activities.
Children who have symptoms of impulsivity may:
• Be very impatient
• Blurt out inappropriate comments, show their emotions without restraint, and act without regard for consequences
• Have difficulty waiting for things they want or waiting their turns in games
• Often interrupt conversations or others’ activities.
ADHD Can Be Mistaken for Other Problems
Parents and teachers can miss the fact that children with symptoms of inattention have ADHD because they are often quiet and less likely to act out. They may sit quietly, seeming to work, but they are often not paying attention to what they are doing. They may get along well with other children, whereas children who have more symptoms of hyperactivity or impulsivity tend to have social problems. But children with the inattentive kind of ADHD are not the only ones whose disorders can be missed. For example, adults may think that children with the hyperactive and impulsive symptoms just have disciplinary problems.
What Causes ADHD?
Scientists are not sure what causes ADHD, although many studies suggest that genes play a large role. Like many other illnesses, ADHD probably results from a combination of factors. In addition to genetics, researchers are looking at possible environmental factors, and are studying how brain injuries, nutrition, and the social environment might contribute to ADHD.
Genes. Inherited from our parents, genes are the “blueprints” for who we are. Results from several international studies of twins show that ADHD often runs in families. Researchers are looking at several genes that may make people more likely to develop the disorder. Knowing the genes involved may one day help researchers prevent the disorder before symptoms develop. Learning about specific genes could also lead to better treatments.
A study of children with ADHD found that those who carry a particular version of a certain gene have thinner brain tissue in the areas of the brain associated with attention. This research showed that the difference was not permanent, however, and as children with this gene grew up, the brain developed to a normal level of thickness. Their ADHD symptoms also improved.
Researchers are also studying genetic variations that may or may not be inherited, such as duplications or deletions of a segment of DNA. These “copy number variations” (CNVs) can include many genes. Some CNVs occur more frequently among people with ADHD than in unaffected people, suggesting a possible role in the development of the disorder.
Environmental factors. Studies suggest a potential link between cigarette smoking and alcohol use during pregnancy and ADHD in children. In addition, preschoolers who are exposed to high levels of lead, which can sometimes be found in plumbing fixtures or paint in old buildings, have a higher risk of developing ADHD.
Brain injuries. Children who have suffered a brain injury may show some behaviors similar to those of ADHD. However, only a small percentage of children with ADHD have suffered a traumatic brain injury.
Sugar. The idea that refined sugar causes ADHD or makes symptoms worse is popular, but more research discounts this theory than supports it. In one study, researchers gave children foods containing either sugar or a sugar substitute every other day. The children who received sugar showed no different behavior or learning capabilities than those who received the sugar substitute. Another study in which children were given higher than average amounts of sugar or sugar substitutes showed similar results.
In another study, children who were considered sugar-sensitive by their mothers were given the sugar substitute aspartame, also known as Nutrasweet. Although all the children got aspartame, half their mothers were told their children were given sugar, and the other half were told their children were given aspartame. The mothers who thought their children had gotten sugar rated them as more hyperactive than the other children and were more critical of their behavior, compared to mothers who thought their children received aspartame.
Food additives. There is currently no research showing that artificial food coloring causes ADHD. However, a small number of children with ADHD may be sensitive to food dyes, artificial flavors, preservatives, or other food additives. They may experience fewer ADHD symptoms on a diet without additives, but such diets are often difficult to maintain.
If you would like the full text of this publication, it is in the public domain and available at no cost at http://www.nimh.nih.gov/health/publications/attention-deficit-hyperactivity-disorder/index.shtml
If you would like to read this entire booklet and receive one hour of continuing education credit, visit Professional Development Resources at https://pdresources.org/course/index/6/1167/Attention-Deficit-Hyperactivity-Disorder-ADHD
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