Although Attention Deficit Disorder, or ADHD, is not typically diagnosed until years later, some sign of this neurobehavioral deficit can already be seen in the brain structure and functions of an infant. Actually, it is possible that the very first signs of ADHD are seen in the brain structure and only after a while, do these abnormalities manifest themselves in the impulsive behavior, inattentiveness and hyperactivity that is so characteristic for the ADHD.
Orbitofrontal Cortex
It is normal for a healthy, young infant to be unable to postpone gratification. When a child grows, he learns to wait for his rewards. The development of such emotional self-regulation is dependent on building connections between cortical and limbic structures in the infant brain and the maturation of the right orbitofrontal cortex. Dr. Panzer A. Viljoen states, however, that this may not happen in an infant suffering from ADHD. These areas mature extremely slowly, if at all in them, and the infants remain stuck in a phase where he is unable to wait for any rewards. His study was published in he "Medical Hypotheses Journal" in 2005. This might explain the impulsivity and aggressive reactions seen in some ADHD patients even as adults.
Blood Flow And Dopamine
Some neurotransmitter, or a chemical that neurons use to communicate, have been connected to ADHD. One of the most well-known of these is dopamine that is linked to memory and attention. It has also been shown, that ADHD patients have reduced blood circulation especially in the frontal lobes, indicating low neural activity in this area as shown by Dr. Francisco Xavier Castellanos in a study that was published in 1997 in "Clinical Pediatrics" Journal. Hans C. Lou, Ph.D. and colleagues, studied six adolescents with ADHD who had had their blood flow in the brain measured as newborns. The authors noticed that there was a correlation between the blood flow and amount of dopamine receptors. If the adolescent had diminished blood flow in their brain as newborns, they had more dopamine receptors as adolescent. The study was published in the "Developmental Medicine and Child Neurology" in 2004. Thus, the reduced blood flow seen in adults and children with ADHD can already be present in infancy and cause the increase in the dopamine receptors later in life.
Brain Maturation And Volume
The brain of a child with ADHD matures approximately three years later than that of a healthy child, says the National Institute for Mental Health in 2007. The only exception is the motor cortex that seems to mature more rapidly in children with ADHD than in the healthy controls. A study published in 2002 in "JAMA" also stated that children with ADHD had a smaller brain size than their healthy controls. None of these differences have been reported in infants with or without risk for ADHD, however.
Reticular Activating System
The reticular activating system, or RAS, is an area in the brainstem that is responsible for regulation sleep, wakefulness, and arousal. It has been shown to have overactive in some ADHD patients with hyperactivity symptoms says the ADD101.com. Dr. Malena Thunström showed in a study published in vol 5 of the "Acta Paediatrica" Journal in 2002 that severe sleep problems in infancy were associated with ADHD diagnosis five years later. Thus, it is possible that the reticular activation is abnormal already in infancy.
Different From Birth?
As a summary, it seems that there is a great variance in how quickly some of the ADHD related abnormalities can be seen in the brain structure and functions. Some of them, such as diminished blood flow or increased RAS activity, seem to be present in early infancy whereas some others, such as decreased brain volume or slow maturation can take years to be seen. One must take into account, however, that infant ADHD studies are rare, due to the fact, that most children are not diagnosed with this disorder until years later. Thus, it is possible, that some other brain structures and functions are different from birth in ADHD children but they just have not been investigated yet.
References
- PubMed: Acta Pediatrica: Severe sleep problems in infancy associated with subsequent development of attention-deficit/hyperactivity disorder at 5.5 years of age.
- PubMed: Developmental Medicine & Child Neurology: ADHD: Increased Dopamine Receptor Availability Linked to Attention Deficit
- "Clinical Pediatrics" Journal; Toward a pathophysiology of attention-deficit/hyperactivity disorder.; F.X. Castellanos; vol. 7, 381-393, 1997.
- National Institute of Mental Health: Brain Matures a Few Years Late in ADHD
- "Jama" Journal; Developmental trajectories of brain volume abnormalities in children and adolescents with attention-deficit/hyperactivity disorder
