Pathophysiology (Brain Differences in AD/HD)

Neurochemistry

Structural and functional imaging research on the neurochemistry of AD/HD implicate the catecholamine-rich fronto-subcortical systems in the pathophysiology of AD/HD. The effectiveness of stimulant medication, along with animal models of hyperactivity, also point to catecholamine disruption as at least one source of AD/HD brain dysfunction.

A 10-year study by National Institute of Mental Health the found that brains of children and adolescents with AD/HD are 3-4% smaller than those of children who don't have the disorder - and that medication treatment is not the cause (JAMA 2002 Oct 9; 288(14):1740-8).

Basic neuroimaging research is being conducted to further delineate the pathophysiology of AD/HD, determine diagnostic utility of neuroimaging, and elucidate the physiological effects of treatment.  However, the research is not definitive enough for practical application of neuroimaging.

Executive Function

Many of the symptoms classifed as AD/HD symptoms of inattention are actually symptoms of executive function impairments. Executive function refers to a wide range of central control processes in the brain that activate, integrate, and manage other brain functions.

Best put, Thomas E. Brown, Ph.D., of Yale University compares executive function to the conductor of an orchestra.  The conductor organizes, activates, focuses, integrates, and directs the musicians as they play, enabling the orchestra to produce complex music. Similarly, the brain's executive functions organize, activate, focus, integrate and direct, allowing the brain to perform both routine and creative work. 

The components of executive function that impact functioning at school or work:

• working memory and recall (holding facts in mind while manipulating information; accessing facts stored in long-term memory)
• activation, arousal and effort (getting started; paying attention; completing work)
• emotion control (tolerating frustration; thinking before acting or speaking)
• internalizing language (using self-talk to control one's behavior and direct future actions)
• complex problem solving (taking an issue apart, analyzing the pieces, reconstituting and organizing them into new ideas)

References

Brown, T. (Ed.) (2000). Attention deficit disorders and comorbidities in children, adolescents, and adults.  Washington, D.C.: American Psychiatric Press.

Dendy, C. (2002, February). 5 Components of Executive Function and How They Impact School Performance. Attention!, 26-31.

Other Web Sites:

• Brain Imaging in Children with AD/HD
  Researchers at the National Institute of Mental Health found that brains of youth with AD/HD are 3-4% smaller than youth without AD/HD.
• APA Statement on Brain Imaging and SPECT
  Statement from the American Psychiatric Association on "Brain Imaging and Child and Adolescent Psychiatry With Special Emphasis on SPECT" (single photon emission computerized tomography)