November 10, 2012
Influence of ADHD Medications On Brain’s Reward System Studied
redOrbit Staff & Wire Reports — Your Universe Online
Some drugs used to treat ADHD could affect the brain's reward system, researchers from the University of Copenhagen have discovered.
The findings make it easier to understand how the medicine works and could ultimately lead to improvements in the development of and the dose determination associated with ADHD treatments, they report in the latest edition of the Journal of Neurophysiology.
As part of the study, Jakob Kisbye Dreyer, a postdoctoral candidate at the university's Department of Neuroscience and Pharmacology, and colleagues developed a new mathematical reconstruction of the portion of the brain responsible for registering both reward and punishment.
When the signals associated with both sensations run through a person's brain, it always involved the chemical dopamine, the university explained in a statement.
"It has been discussed for years whether treating ADHD with Ritalin and similar drugs affects the reward system to any significant degree, simply because the dosage given to patients is so low," Dreyes said. "We are the first to show that some components of the dopamine signaling pathways are extremely sensitive to drugs like Ritalin. We have also developed a unified theory to describe the effect of such drugs on the dopamine signal."
The research was inspired by the high rate of ADHD among school-aged youngsters in Denmark, which could be as much as 3%, the university said. Dreyes said it is vital to know what exactly happens in the brain when the condition is being treated with Ritalin or similar drugs, in order to help develop more effective treatment options and to gain a greater understanding of the underlying psychology of the ailment.
"In the brain, dopamine contributes to series of processes that control our behavior," the university explains. "Actions such as eating, winning a competition, having sex or taking a narcotic drug increase dopamine release. Scientists think that dopamine helps motivate us to repeat actions that have previously been associated with reward."
"Control mechanisms in the brain help keep the dopamine signal in balance so we can register the tiny deviations that signal reward and punishment," Dreyer added. "We discovered while trying to describe these control mechanisms that our model can be used to examine the influence of Ritalin, for example, on the signal. Suddenly we could see that different pathways of the reward system are affected to different degrees by the medicine, and we could calculate at what dosage different parts of the signal would be changed or destroyed."
Ritalin and similar medicine can have contrasting effects based on the doses, with higher doses increasing a patient's activity level and lower ones reducing it. That can make it difficult to determine exactly how much a patient should take in order to treat his or her ADHD, the university said.
"We can explain this double effect using our theory," Dreyer explained. "The dopamine signal in the part of the brain that controls our motor behavior is only affected at a higher dose that the dose usually prescribed for treatment. Also, our model shows that the threshold between a clinically effective dose and too high a dose is very low. That may explain why the small individual differences between patients have a big impact on treatment."