Posts tagged ADHD

July 23, 2012

Ever wonder how the human brain, which is constantly bombarded with millions of pieces of visual information, can filter out what’s unimportant and focus on what’s most useful?

The process is known as selective attention and scientists have long debated how it works. But now, researchers at Wake Forest Baptist Medical Center have discovered an important clue. Evidence from an animal study, published in the July 22 online edition of the journal Nature Neuroscience, shows that the prefrontal cortex is involved in a previously unknown way.

Two types of attention are utilized in the selective attention process – bottom up and top down. Bottom-up attention is automatically guided to images that stand out from a background by virtue of color, shape or motion, such as a billboard on a highway. Top-down attention occurs when one’s focus is consciously shifted to look for a known target in a visual scene, as when searching for a relative in a crowd.

Traditionally, scientists have believed that separate areas of the brain controlled these two processes, with bottom-up attention occurring in the posterior parietal cortex and top-down attention occurring in the prefrontal cortex.

"Our findings provide insights on the neural mechanisms behind the guidance of attention," said Christos Constantinidis, Ph.D., associate professor of neurobiology and anatomy at Wake Forest Baptist and senior author of the study. "This has implications for conditions such as attention deficit hyperactivity disorder (ADHD), which affects millions of people worldwide. People with ADHD have difficulty filtering information and focusing attention. Our findings suggest that both the ability to focus attention intentionally and shifting attention to eye-catching but sometimes unimportant stimuli depend on the prefrontal cortex."

In the Wake Forest Baptist study, two monkeys were trained to detect images on a computer screen while activity in both areas of the brain was recorded. The visual display was designed to let one image “pop out” due to its color difference from the background, such as a red circle surrounded by green. To trigger bottom-up attention, neither the identity nor the location of the pop-out image could be predicted before it appeared. The monkeys indicated that they detected the pop-out image by pushing a lever.

The neural activity associated with identifying the pop-out images occurred in the prefrontal cortex at the same time as in the posterior parietal cortex. This unexpected finding indicates early involvement of the prefrontal cortex in bottom-up attention, in addition to its known role in top-down attention, and provides new insights into the neural mechanisms of attention.

"We hope that our findings will guide future work targeting attention deficits," Constantinidis said.

Provided by Wake Forest University Baptist Medical Center

Source: medicalxpress.com

July 18, 2012

Drugs used to treat Attention Deficit Hyperactivity Disorder (ADHD) do not appear to have long-term effects on the brain, according to new animal research from Wake Forest Baptist Medical Center.

As many as five to seven percent of elementary school children are diagnosed with ADHD, a behavioral disorder that causes problems with inattentiveness, over-activity, impulsivity, or a combination of these traits. Many of these children are treated with psychostimulant drugs, and while doctors and scientists know a lot about how these drugs work and their effectiveness, little is known about their long-term effects.

Linda Porrino, Ph.D., professor and chair of the Department of Physiology and Pharmacology, along with fellow professor Michael A. Nader, Ph.D., both of Wake Forest Baptist, and colleagues conducted an animal study to determine what the long-lasting effects may be. Their findings were surprising, said Porrino. “We know that the drugs used to treat ADHD are very effective, but there have always been concerns about the long-lasting effects of these drugs,” Porrino said.

"We didn’t know whether taking these drugs over a long period could harm brain development in some way or possibly lead to abuse of drugs later in adolescence."

Findings from the Wake Forest Baptist research are published online this month in the journal Neuropsychopharmacology.

The researchers studied 16 juvenile non-human primates, whose ages were equivalent to 6-to 10-year-old humans. Eight animals were in the control group that did not receive any drug treatment and the other eight were treated with a therapeutic-level dose of an extended-release form of Ritalin, or methylphenidate (MPH), for over a year, which is equivalent to about four years in children. Imaging of the animals’ brains, both before and after the study, was conducted on both groups to measure brain chemistry and structure. The researchers also looked at developmental milestones to address concerns that ADHD drugs adversely affect physical growth.

Once the MPH treatment and imaging studies were concluded, the animals were given the opportunity to self administer cocaine over several months. Nader measured their propensity to acquire the drug and looked at how rapidly and in what amounts, to provide an index of vulnerability to substance abuse in adolescence. As reported in the research paper, they found no differences between groups – monkeys treated with Ritalin during adolescence were not more vulnerable to later drug use than the control animals.

"After one year of drug therapy, we found no long-lasting effects on the neurochemistry of the brain, no changes in the structure of the developing brain. There was also no increase in the susceptibility for drug abuse later in adolescence," Porrino said. "We were very careful to give the drugs in the same doses that would be given to children. That’s one of the great advantages of our study is that it’s directly translatable to children."

Porrino said non-human primates provide exceptional models for developmental research because they undergo relatively long childhood and adolescent periods marked by hormonal and physiological maturation much like humans.

"Our study showed that long-term therapeutic use of drugs to treat ADHD does not cause long-term negative effects on the developing brain, and importantly, it doesn’t put children at risk for substance abuse later in adolescence," she said.

One of the exciting things about this research, Porrino said, is that a “sister” study was conducted simultaneously at John Hopkins with slightly older aged animals and different drugs and their findings were similar. “We feel very confident of the results because we have replicated each other’s studies within the same time frame and gotten similar results,” she said. “We think that’s pretty powerful and reassuring.”

Provided by Wake Forest University Baptist Medical Center

Source: medicalxpress.com

ScienceDaily (June 25, 2012) — A team of researchers led by an epidemiologist at Mount Sinai School of Medicine and University of Iceland has found a correlation between the age at which children with attention-deficit/hyperactivity disorder (ADHD) begin taking medication, and how well they perform on standardized tests, particularly in math.

The study, titled, “A Population-Based Study of Stimulant Drug Treatment of ADHD and Academic Progress in Children,” appears in the July, 2012, edition of Pediatrics, and can be viewed online on June 25. Using data from the Icelandic Medicines Registry and the Database of National Scholastic Examinations, the researchers studied 11,872 Icelandic children born between 1994 and 1996. The children started medication for ADHD at different times between fourth and seventh grades.

The findings showed that children who began drug treatment within 12 months of their fourth-grade test declined 0.3 percent in math by the time they took their seventh-grade test, compared with a decline of 9.4 percent in children who began taking medication 25-to-36 months after their fourth-grade test.

The data also showed that girls benefited only in mathematics, whereas boys had marginal benefits in math and language arts.

"Children who began taking medications immediately after their fourth-grade standardized tests showed the smallest declines in academic performance," said the study’s lead author Helga Zoega, PhD, Post Doctoral Fellow of Epidemiology at Mount Sinai’s Institute for Translational Epidemiology. "The effect was greater in girls than boys and also greater for children who did poorly on their fourth grade test."

Stimulants are widely used in the United States as a therapeutic option for children with inattention, impulsivity, and hyperactivity associated with ADHD. The medications are less frequently used in Europe, although their use in Iceland most closely resembles the U.S. Long-term follow-up studies of stimulant use and academic performance are scarce, according to the researchers.

Source: Science Daily