Attention deficit hyperactivity disorder, or ADHD, is a neurobehavioral disorder that is primarily characterized by hyperactivity, inattentiveness and impulsivity. According to Dr. Katya Rubia, ADHD causes a developmental delay in the brain structures and functions. Thus a child with ADHD appears to behave with the activity and impulsivity of a much younger child. Yet the National Institute for Mental Health reported in 2007 that the motor cortex develops more rapidly in children with ADHD than in their healthy controls, suggesting that ADHD is not simply a developmental delay but rather follows a developmental pattern that is typical for ADHD alone.
Causes of Developmental Changes
The causes of ADHD-related developmental delays and abnormalities in the brain structure and functions and not fully known. Dr. Rubia suggests, however, that they might be caused by both genetic and environmental factors. Frequent failures at school or among friends can put a toll on the patient's social development, for example. It has also been speculated that ADHD medication might affect the developmental outcome of the ADHD patients. F.X. Castellanos and colleagues showed in a study published in the "Journal of American Medical Association" in 2002 that unmedicated ADHD patients had no gray matter abnormalities, but such abnormalities were present in the medicated patients.
Brain Maturation Delays
Several studies have reported that the brains of ADHD patients seem to mature later than those of healthy controls. The National Institute for Mental Health reported in 2007 that the brain maturation was three years behind in middle school-aged ADHD children as compared to their healthy controls. This finding was confirmed by Dr. P. Shaw and colleagues, who followed over 200 ADHD children and their controls for nearly three years. They showed in a study published in the "Proceedings of the National Academy of Sciences Journal" that the development of the prefrontal areas was five years behind in the ADHD children when compared to the healthy children.
Executive Function Delays
Children with ADHD have considerable difficulties in the so-called executive functions of the brain. These include planning, reasoning and decision-making skills. In everyday life, such difficulties can be seen as the inability of an ADHD child to plan how to do a school project. He may have a hard time estimating how much time completing the task is going to take, for example. The late development of such higher cognitive functions is a hallmark of ADHD. These difficulties can be explained by the slow maturity rate of the prefrontal cortex demonstrated by Dr. Shaw and colleagues.
Social and Emotional Development
Another hallmark of ADHD is emotional immaturity, says Russell A. Barkley, Ph.D. A child with ADHD may come across as much younger than he is. He might have difficulties making friends. The social difficulties can partly be explained by the inability of an ADHD child to follow different social rules. He may have a hard time waiting for his turn, he does not seem to listen, and he tends to interrupt people.
Physical Development
Dr. Pelham and colleagues showed that children with ADHD tend to be shorter and lighter than their healthy controls. The authors concluded that this might be due to the ADHD medication because such growth reduction can only be seen with patients who are on ADHD medication.
References
- Proc Natl Acad Sci: Neuro-Anatomic Evidence for the Maturational Delay Hypothesis of ADHD
- "J Am Med Assoc"; On Brain-Volume Abnormalities in Children with ADHD; FX Castellanos et al; vol 288, 2002
- "National Institute of Mental Health" Press Release; Brain Matures a Few Years Late in ADHD, But Follows Normal Pattern.; Shaw, Rapoport, Evans; Nov. 2007.
- Proc Natl Acad Sci: ADHD Is Characterized by a Delay in Cortical Maturation
- Continuing Education Courses: Attention-Deficit/Hyperactivity Disorder: Nature, Course, Outcomes, and Comorbidity
