Researchers at the National Institute of Mental Health recently studied children with attention disorders and found abnormalities in three brain structures involved in controlling mental activity. Studies show subtle abnormalities in the right side of the brain, responsible for inhibiting thought patterns, that may cause the disorder.
In most boys, the brain's right cerebral hemisphere is larger than the left. In those with attention deficit disorders, however, the right side is noticeably smaller, brain scans show.
But researchers also have discovered that these children with brain abnormalities had a history of complications before and after birth. That led some researchers to consider whether events in the womb may have affected neural development.
Still other studies suggest that childhood exposure to lead increases the risk of hyperactivity.
To complicate matters further, there is evidence that at least some cases of attention disorder have a genetic basis. Dr. Judith Rapoport, chief of the NIMH Child Psychiatry Branch, suggested that a predisposition to prenatal viral infections could be involved as well.
Exposure to alcohol, cocaine and radiation also can hinder the migration of neurons during fetal development, which could in turn cause the brain abnormalities linked to the disorder. Some experts even theorize that these children's problems may be caused by an inability to properly metabolize key fatty acids in their food, or by too much television.
"The first step in really being able to help people with different psychiatric disorders like ADHD is to better understand the neurology of the disorder and what brain areas might be involved," said neuroscientist Robert Farber at UC San Diego.
"That ultimately will help us, not only in our ability to clinically evaluate patients, but also to find ways to better treat these disorders."
To that end, Schweitzer's high-speed PET scans of the brains of people diagnosed with ADHD may be of help. The scans reveal a paradox: The easier a task becomes, the harder it is for ADHD patients to stay focused on it.
Standard teaching techniques utilizing repetition and rote learning, which help most people master new information, appear to make it harder for someone with the disorder to stay focused. The more routine the task becomes, the harder it is for the patient to pay attention.
"They make more mistakes as time wears on," said Schweitzer. "They become more impulsive, more hyperactive."
"The details of these types of findings will be of interest to researchers designing new drugs targeted to affected brain regions and to educators designing teaching tools for children and adults with ADHD," she said.
(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)
Trouble in Mind
New brain scans show that people with attention deficit hyperactivity disorder (ADHD) handle mental tasks very differently than people unaffected by the disorder.
Using a PET scanner, which makes a series of slice-like images of the brain at work, experts studied the brains of people with ADHD and a control group as they added numbers.
Disruption of Working Memory
The typical ADHD brain, bottom row above, is not as active as the unaffected brain, top row, in neural regions thought to be important in short-term memory and directing new information to other parts of the brain. The yellow areas indicated increased blood flow and metabolic activity. The scans of slices of ADHD brains show much less activity on frontal brain areas and more compensatory brain activity in other areas.
Neuroscientists at Emory University in Atlanta say the difference could help explain why ADHD patients have so much trouble paying attention.
Routine Dulls ADHD Performance
When a normal person practices a task, key parts of the brain become more active, left. But for a person with ADHD, right, brain performance does not improve with practice, as indicated by the absence of activity (in yellow) in frontal brain areas. In fact, it becomes harder over time for ADHD suffers to pay attention, researchers say.
* Source: Emory University, School of Medicine.