Paying Attention
Their fingers fidget. Their eyes dart. Impulsive, aggressive and often self-destructive, they blurt out their thoughts and squirm as if unable to contain themselves, almost willful in their inability to mind.
These are children suffering from attention deficit hyperactivity disorder--the most common psychiatric condition found among young people. Difficult to diagnose and even harder to correct, the disorder has spawned special learning plans, curative diets, neuro-feedback treatments and a range of prescription stimulants designed to improve concentration and attention span.
Yet the biology behind this behavior remains a mystery to those trying to treat it.
Now researchers peering into these troubled brains have discovered that such children may be locked in a fierce struggle with forgetfulness.
New brain imaging studies of adults who had been diagnosed with the disorder as children reveal what appear to be flaws in neural regions that temporarily store and handle new information, according to neuroscientists at Emory University in Atlanta.
Located in the brain’s prefrontal cortex, this area is believed to be a kind of central executive that filters new information, parceling it out to other areas where it can be acted upon. Disruption of this working memory could explain why people with the disorder have such a hard time paying attention, experts said.
Able to maintain only a slippery mental grasp on any matter at hand, they have more difficulty adding numbers, reading a book or remembering to finish a chore, the studies show. No matter how hard they try, their concentration is continuously disrupted by unwanted thoughts.
“When we are working and thinking, our brain is doing multiple things at once and we need to learn to focus in on what we need to do,” said Emory psychiatrist Julie Schweitzer, who used positron emission tomography (PET) to conduct the first studies of working memory in people with the disorder. “This is what these people have a hard time doing.”
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Indeed, new brain images by researchers at Wake Forest University Medical School show that the strain of holding on to a thought long enough to pay sustained attention to it makes their brains work even harder than those of other children, as their minds try to overcome the flaws in their neural circuitry.
“They try to compensate for their problems,” said neuropsychologist Frank Wood, who conducted the study with researcher Lynn Flowers at Wake Forest. “Areas that gather information about what is going on in the world and make plans for the future seem to work harder.”
They also may press other areas of the brain into service. For example, patients with the disorder who were asked to listen to a series of numbers and add them in a sequence could not handle the arithmetic the way most people do, by listening intently and, perhaps, repeating key numbers mentally to keep track of them. Instead, they had to visualize the stream of numbers to keep their attention focused, Schweitzer found.
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The new insights into the neurobiology of attention deficit disorder, reported recently at a meeting of the Society for Neuroscience, arise as scientists search for the links between the physical structure of the brain and a range of mental disturbances.
Using brain scanners that track blood flow and metabolic rates in living neural tissues, these researchers are shining a light into the shadows of the conscious mind.
Higher brain functions such as learning, memory and intellectual ability exist, like constellations of stars, as networks of neurons in an inner universe composed of billions of interconnected brain cells. In most brains, they somehow weave together into the skein of a coherent, healthy personality.
But subtle alterations in physical brain function, as measured by new scanning techniques, appear to manifest themselves as disabling behavioral problems.
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Recent research, for example, at UC Irvine and other universities suggests that mental disorders such as schizophrenia, autism and severe infantile epilepsy may all stem from problems that occur when neurons and neural circuits malfunction. Other brain imaging studies suggest that minor alterations in the neural circuits responsible for vision and hearing may be responsible for dyslexia.
Despite the compelling evidence of such brain studies, however, researchers caution that the relationship among genes, upbringing, the environment and the structure of the developing brain is so complex that it is hard to know which--if any--might be the source of a problem behavior.
The search for the cause of attention deficit disorders, which affect 5% to 9% of school-age children, highlights the difficulty in sorting behavioral cause from effect, even with the aid of new brain scanning techniques.
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.
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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.”
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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.
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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.
