Posted by MAC

The following report from the AMA was published in Scientific America last
year.(clipped for brevity)

IN FOCUS

PAYING ATTENTION
The controversy over ADHD
and the drug Ritalin is obscuring a real look
at the disorder and its underpinnings

It will be difficult, though, to move from making moral diagnoses to medical
ones because all the available tests for mental illness are so subjective.
The criteria set forth for ADHD in the DSM-IV require that a child display a
range of symptoms, such as distractibility and a short attention span, that
are excessive for his or her mental age. Moreover, these symptoms must
persist for at least six months and significantly impair the child's ability
to function.

Nearly all children exhibit some of these symptoms some of the time. And
ADHD falls along a spectrum, as do all psychological disorders. "Where we
draw the line along that spectrum determines how many people have it,"
Barkley notes. Making diagnosis even more difficult is the fact that ADHD
frequently appears with other disorders, including Tourette's syndrome, lead
poisoning, fetal alcohol syndrome and retardation. In addition, many other
conditions-such as depression, manic-depressive illness, substance abuse,
anxiety and personality disorders-share similar symptoms.

Nevertheless, the biology behind ADHD is beginning to surface. "We cannot
say which structure or which chemical is wrong," emphasizes Alan Zametkin of
the National Institute of Mental Health (NIMH). "ADHD is like fever-any
number of causes can be to blame." But he has found, for example, that a
small subset of ADHD people have a different receptor for thyroid hormone
and that 70 to 80 percent of all people with this very rare difference in
their thyroid receptor have ADHD.

Other studies have found an association between ADHD and three genes
encoding receptors for the neurotransmitter dopamine. Collaborating with
molecular biologists and geneticists at Irvine and at the University of
Toronto, Swanson examined the so-called novelty-seeking gene, which codes
for the dopamine receptor DRD4. One series of base pairs repeats two, four
or seven times. More repeats are associated with a blunted response to
dopamine signals and less inhibited behavior. "We found that the
seven-repeat variety of the gene is overrepresented among ADHD children,"
Swanson says.

Neurochemistry is not the whole story. Scientists have also discovered
structural abnormalities. F. Xavier Castellanos of the NIMH used magnetic
resonance imaging to measure the total brain volume and several different
brain regions in 57 ADHD boys and 55 healthy control subjects. His team
found that the anterior frontal part of the brain was on average more than 5
percent smaller on the right side in ADHD boys. The right caudate and the
globus pallidus, too, were smaller. These structures form the main neural
circuit by which the cortex inhibits behavior, and so damage there might
well manifest itself as a lack of impulse control. Castellanos warns that
this result offers but part of the puzzle: "It's only slightly better than
phrenology. Now we're just measuring the bumps on the inside of the brain."

Another facet of ADHD malfunctioning comes from positron emission tomography
(PET) studies. Julie B. Schweitzer of Emory University monitored brain
activity in ADHD and unaffected men while they completed a task.
Participants heard a series of numbers, one every 2.4 seconds, and were
asked to add the last two digits they heard. Looking at the PET scans,
Schweitzer saw two major differences between the groups. First, the ADHD
individuals maintained high levels of blood fiow, whereas the controls
displayed deactivation in the temporal gyrus region-indicating some kind of
learning.

The ADHD group also activated brain areas used for visual tasks. "I went
back and asked the ADHD subjects if they used some strategy," Schweitzer
says. "Instead of repeating the numbers to themselves, as some of the
controls did, many ADHD patients had visualized them." She suggests that
this visualization represents some kind of compensation for impaired
cognition elsewhere. Zametkin, too, has used PET scans to study ADHD. He
took images of parents of ADHD children and found that they exhibit less
brain activity. He concludes, "These kids really are born to be
wild." -Kristin Leutwyler

Follow Ups:

• Re: Tha Cause of ADHD Lydia Porter
• Re: Tha Cause of ADHD Nicole Dickinson

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