Attention deficit hyperactivity disorder (ADHD) is a disorder diagnosed in childhood where children have difficulties maintaining attention and controlling hyperactive and impulsive behaviors. As reported by the Centers for Disease Control, about 7 percent of children are diagnosed with ADHD. The development of the disorder is thought to be attributable in part to biological factors, which include the role of genetics, difference in brain structure and early developmental risks.
Genetics
The National Institute of Mental Health suggests that genes play an important role in the development of ADHD. The results of twin studies suggest that there is a high rate of inheritability for ADHD. The disorder tends to run in families, meaning that children whose parents or siblings have ADHD are at higher risk. Research is currently working to identify specific genes indicative of ADHD in hopes of prevention.
According to Robert Weis in "Introduction to Child and Adolescent Psychology," genes involved in the dopamine neurotransmitter system are thought to be involved in the development of ADHD. ADHD medications help to stimulate the dopamine system and dopamine receptors play an important role in attention and controlling behavior, both of which are significant symptoms of ADHD. These findings seem to suggest that the genes in this system are involved; however, further research will help to clarify this hypothesis.
Brain Structures
There are specific brain regions thought to function differently in children with ADHD. As described by Weis, research has found differences in the size and manner of functioning in the prefrontal cortex of children with ADHD. The prefrontal cortex controls executive functioning and the ability to process information, organize, plan, problem solve and avoid distractions. Children with ADHD tend to struggle with these tasks. Subsections of the prefrontal cortex known as the orbital and dorsolateral prefrontal regions help the child to control impulses and organize and plan, respectively. In children with ADHD, these areas of the brain are smaller.
The basal ganglia is connected to the prefrontal cortex and sends information regarding memory, attention and action. This information pathway is thought to function ineffectively in children with ADHD. Additionally, some areas of the basal ganglia are thought to function abnormally, leading to difficulties regulating behavior and attention.
Early Development
Another biological factor that contributes to ADHD occurring during early development is use of alcohol or smoking cigarettes by pregnant mothers, according to the National Institute of Mental Health. Also, exposure to high levels of lead at a young age has also been linked to a diagnosis of ADHD. Additionally, oxygen deprivation prenatally or at birth is thought to strongly impact areas of the brain that control behavior and executive functions.
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
