Etiology

ADHD: Fact, Fiction and Beyond
A Comprehensive Study of Attention Deficit Hyperactivity Disorder
by Dr. Victoria Martin, M.D.

There is much speculation about the cause of ADHD.  In November, 1996, the journal of the American Academy of Child And Adolescent Psychiatry published an article by Biederman and Faraone indicating a 10% increase in ADHD children with learning disabilities and without other psychiatric comorbidity born in the month of September.  This might suggest a winter infection during early pregnancy.  Other suggested causes have been impaired glucose metabolism in the prefrontal cortex and pre-motor cortex causing an inability to inhibit inappropriate responses, malfunctioning in a gene controlling regulation of thyroid hormone, and deficits in the prefrontal cortex and caudate nucleus.

Over the last 10 years neuroscientists have become increasingly aware of the role of inhibitory parts of the nervous system and the importance of the regulatory functions that inhibition provides.  Prior to that time we thought the cholinergic and adrenergic systems were what was important because they made things happen that we could see and measure.  Now we know that only about 10% of the brain works on a cholinergic/adrenergic basis.  Five percent is involved with those functions we call collectively “awareness.”  The rest (85% of the brain mass) is inhibitory in function.

The new theories of ADHD emphasize a relative failure of neural inhibition as the core problem.  Distractibility is conceptualized as a failure to inhibit and suppress other stimuli from awareness.  The impulsivity and hyperactivity components may be conceptualized as the partial failure of the frontal lobes whose job it is to inhibit and control emotion responses, inappropriate cognitive and psychic responses, and behavioral impulses.   In fact the functions of the prefrontal cortex are maintaining attention, perseverance, judgment, impulse control, organization, self-monitoring and supervision, problem solving, critical thinking, forward thinking, learning from experience, ability to feel and express emotions, and empathy.  In short, the same things that ADHD people have problems with!

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