ADHD medicine affects the brain's reward system

ADHD medicine affects the brain's reward system
The scientists' model shows how some types of ADHD medicine influence the brain's reward system.

(Medical Xpress)—A group of scientists from the University of Copenhagen has created a model that shows how some types of ADHD medicine influence the brain's reward system. The model makes it possible to understand the effect of the medicine and perhaps in the longer term to improve the development of medicine and dose determination. The new research results have been published in the Journal of Neurophysiology.

In Denmark approximately 2-3 per cent of school-age children satisfy for ADHD, and therefore it is crucial to know how the medicine works. With a new mathematical of a tiny part of the brain region that registers reward and punishment, scientists from the University of Copenhagen are acquiring new knowledge about the effect of ADHD medicine. When reward and punishment signals run through the brain, the is always involved.

"It has been discussed for years whether treating ADHD with Ritalin and similar drugs affects the to any significant degree, simply because the dosage given to patients is so low. We are the first to show that some components of the dopamine signalling 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," says Jakob Kisbye Dreyer, postdoctoral candidate at the Department of and Pharmacology, Faculty of Medical and Health Sciences, University of Copenhagen, where the model was developed.

He emphasises the importance of knowing exactly what happens during treatment with drugs like Ritalin. This is in order to develop better and more targeted medicine, as well as to understand the psychology underlying ADHD. The actions of human beings are motivated by an unconscious calculation of cost relative to expected gain. The scientists' results show that ADHD medicine specifically reduces signals about anticipated punishment.

Reward and punishment

In the brain, dopamine contributes to series of processes that control our behaviour. 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. 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," says Jakob Kisbye Dreyer.

Different dosage, different effect

Drugs such as can have paradoxical effects: high dosage increases the patient's activity while low dosage reduces it. Therefore it can be a laborious process to find the right dosage for a patient.

"We can explain this double effect using our theory. The dopamine signal in the part of the brain that controls our motor behaviour 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," says Jakob Kisbye Dreyer.

In the long term, the scientists hope that their new insight will help doctors determine the correct dose for each patient. The model can also help us understand what signals in the brain affect not only , but schizophrenia, Parkinson's disease and drug abuse as well.

More information: jn.physiology.org/content/earl… .00502.2012.abstract

Related Stories

Adult ADHD linked with dopamine levels

Aug 09, 2007

Adults with attention-deficit/hyperactivity disorder have a reduced response to the drug Ritalin, U.S. government scientists have found.

Deficits in brain's reward system observed in ADHD patients

Sep 08, 2009

A brain-imaging study conducted at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory provides the first definitive evidence that patients suffering from attention deficit hyperactivity disorder (ADHD) have ...

Patients' brains may adapt to ADHD medication

Feb 02, 2012

(Medical Xpress) -- New research reveals how the brain appears to adapt to compensate for the effects of long-term ADHD medication, suggesting why ADHD medication is more effective short-term than it is long-term. ...

Recommended for you

Emotional adjustment following traumatic brain injury

1 hour ago

Life after a traumatic brain injury resulting from a car accident, a bad fall or a neurodegenerative disease changes a person forever. But the injury doesn't solely affect the survivor – the lives of their spouse or partner ...

New ALS associated gene identified using innovative strategy

Oct 22, 2014

Using an innovative exome sequencing strategy, a team of international scientists led by John Landers, PhD, at the University of Massachusetts Medical School has shown that TUBA4A, the gene encoding the Tubulin Alpha 4A protein, ...

Can bariatric surgery lead to severe headache?

Oct 22, 2014

Bariatric surgery may be a risk factor for a condition that causes severe headaches, according to a study published in the October 22, 2014, online issue of Neurology, the medical journal of the American Academy of Neurol ...

User comments