The predominant symptoms of attention deficit hyperactivity disorder, or ADHD, are the inability to sustain attention and difficulty controlling impulsive and hyperactive behaviors. According to the Centers for Disease Control and Prevention, 7 percent of children in the U.S. between the ages of 5 and 17 are diagnosed with the disorder. Several risk factors have been linked to the development of ADHD, including genetics, brain functioning, early development, and other environmental risks.
Genetics
According to the National Institute for Mental Health, genes are thought to play an important role in the development of ADHD. Findings from twin studies suggest that the disorder is highly inheritable, meaning that it tends to run in families. Children with parents or siblings diagnosed with the disorder are at increased risk. Research is now focused on finding specific genes that are indicative of the disorder. As described by Robert Weis in "Introduction to Abnormal Child and Adolescent Psychology," genes in the dopamine neurotransmitter system are thought to be involved in the development of ADHD as they play an important role in controlling behavior and regulating attention.
Brain Functioning: Prefrontal Cortex
As discussed by Weis, the prefrontal cortex controls executive functioning, which is the ability to process information, shift tasks, avoid distractions, organize, plan and problem solve. Children with ADHD predominantly show deficits in these areas. Subsections of the prefrontal cortex, the orbital and dorsolateral regions, are used to control impulses and organize or plan. These regions tend to be smaller and less active in children with ADHD. It is thought that the prefrontal cortex in children with ADHD functions differently than those without the disorder.
Brain Functioning: Basal Ganglia
Another region of the brain implicated in ADHD is the basal ganglia. It is connected to the prefrontal cortex and relays information about attention, action, and memory. This pathway is critical to the performance of the executive functions previously mentioned. In children with ADHD, the pathway functions ineffectively. Also, certain areas of the basal ganglia have been found to have abnormalities and underactivity. The use of stimulant medications has been shown to improve functioning in this area of the brain, suggesting that deficits relate to symptoms of ADHD.
Early Development
According to the National Institute for Mental Health, there are several risk factors in prenatal or early development that contribute to the development of ADHD. Mothers who use alcohol or smoke cigarettes while pregnant are more likely to have children diagnosed with ADHD. Exposure to toxins such as lead have also been linked to the disorder. Additionally, Weis reports that oxygen deprivation to the fetus in utero can damage areas of the brain responsible for controlling behavior and executive functioning.
Other Environmental Risks
There are two other risk factors reported by the National Institute of Mental Health that have been suspected as contributing to the development of ADHD. Refined sugar was thought to exacerbate symptoms of the disorder; however, research has found no support for this claim. Food additives and artificial coloring have also been thought to contribute to ADHD symptoms, but research is still investigating this hypothesis.
References
- Centers for Disease Control and Prevention: Summary of Health Statistics for U.S. Children
- National Institute of Mental Health: What Causes ADHD?
- "Introduction to Abnormal Child and Adolescent Psychology"; Robert Weis; 2008
