Research using advanced imaging techniques shows there is a difference in the size of certain parts of the brain in children with ADHD compared to children who do not have ADHD. The areas showing change include the prefrontal cortex, the caudate nucleus and globus pallidus, and the cerebellum.
Abnormal activity of certain brain chemicals in the prefrontal cortex may contribute to ADHD. The chemicals dopamine and norepinephrine are of special interest. Dopamine and norepinephrine are neurotransmitters, or chemical messengers, that affect both mental and emotional functioning. They also play a role in the "reward response." This response occurs when a person experiences pleasure in response to certain stimuli (such as food or love). Studies suggest that increased levels of the brain chemicals glutamate, glutamine, and GABA -- collectively called Glx -- interact with the pathways that transport dopamine and norepinephrine.
Another area of interest is a network of nerves called the basal-ganglia thalamocortical pathways. Abnormalities along this neural route have been associated with ADHD, Tourette syndrome, and obsessive-compulsive disorders, all of which share certain symptoms.
Genetic factors may play the most important role in ADHD. The relatives of ADHD children (both boys and girls) have much higher rates of ADHD, antisocial, mood, anxiety, and substance abuse disorders than the families of non-ADHD children. Some twin studies report that up to 90% of children with a diagnosis of ADHD shared it with their twin.
Most of the research on the underlying genetic mechanisms targets the neurotransmitter dopamine. Variations in genes that regulate specific dopamine receptors have been identified in a high proportion of people with addictions and ADHD.
Biederman J, Melmed RD, Patel A, McBurnett K, Konow J, Lyne A, et al. A randomized, double-blind, placebo-controlled study of guanfacine extended release in children and adolescents with attention-deficit/hyperactivity disorder. Pediatrics. 2008 Jan;121(1):e73-84.
Braun JM, Kahn RS, Froehlich T, Auinger P, Lanphear BP. Exposures to environmental toxicants and attention deficit hyperactivity disorder in U.S. children. Environ Health Perspect. 2006 Dec;114(12):1904-9.
Hamilton SS, Armando J. Oppositional defiant disorder. Am Fam Physician. 2008 Oct 1;78(7):861-6.
Heinrich H, Gevensleben H, Strehl U. Annotation: neurofeedback - train your brain to train behaviour. J Child Psychol Psychiatry. 2007 Jan;48(1):3-16.
Jensen PS, Arnold LE, Swanson JM, et al. 3-year follow-up of the NIMH MTA study. J Am Acad Child Adolesc Psychiatry. 2007 Aug;46(8):989-1002.
Millichap JG. Etiologic classification of attention-deficit/hyperactivity disorder. Pediatrics. 2008 Feb;121(2):e358-65.
Nigg JT, Breslau N. Prenatal smoking exposure, low birth weight, and disruptive behavior disorders. J Am Acad Child Adolesc Psychiatry. 2007 Mar;46(3):362-9.
Perrin JM, Friedman RA, Knilans TK; Black Box Working Group; Section on Cardiology and Cardiac Surgery. Cardiovascular monitoring and stimulant drugs for attention-deficit/hyperactivity disorder. Pediatrics. 2008 Aug;122(2):451-3.
Pliszka S; AACAP Work Group on Quality Issues. Practice parameter for the assessment and treatment of children and adolescents with attention-deficit/hyperactivity disorder. J Am Acad Child Adolesc Psychiatry. 2007 Jul;46(7):894-921.
Steiner H, Remsing L; Work Group on Quality Issues. Practice parameter for the assessment and treatment of children and adolescents with oppositional defiant disorder. J Am Acad Child Adolesc Psychiatry. 2007 Jan;46(1):126-41.
Swanson JM, Elliott GR, Greenhill LL, et al. Effects of stimulant medication on growth rates across 3 years in the MTA follow-up. J Am Acad Child Adolesc Psychiatry. 2007 Aug;46(8):1015-27.
Valera EM, Faraone SV, Murray KE, Seidman LJ. Meta-analysis of structural imaging findings in attention-deficit/hyperactivity disorder. Psychiatry. 2007 Jun 15;61(12):1361-9. Epub 2006 Sep 1.
Vetter VL, Elia J, Erickson C, Berger S, Blum N, Uzark K, et al. Cardiovascular monitoring of children and adolescents with heart disease receiving stimulant drugs: a scientific statement from the American Heart Association Council on Cardiovascular Disease in the Young Congenital Cardiac Defects Committee and the Council on Cardiovascular Nursing. Circulation. 2008 May 6;117(18):2407-23. Epub 2008 Apr 21.
Weber W, Vander Stoep A, McCarty RL, Weiss NS, Biederman J, McClellan J. Hypericum perforatum (St John's wort) for attention-deficit/hyperactivity disorder in children and adolescents: a randomized controlled trial. JAMA. 2008 Jun 11;299(22):2633-41.
Wilens TE, Upadhyaya HP. Impact of substance use disorder on ADHD and its treatment. J Clin Psychiatry. 2007 Aug;68(8):e20.
Williams JH, Ross L. Consequences of prenatal toxin exposure for mental health in children and adolescents: a systematic review. Eur Child Adolesc Psychiatry. 2007 Jun;16(4):243-53. Epub 2007 Jan 2.
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