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 lower-than-normal levels of certain proteins essential for experiencing reward and motivation.

"These deficits in the brain's may help explain clinical symptoms of ADHD, including inattention and reduced motivation, as well as the propensity for complications such as and obesity among ADHD patients," said lead author Nora Volkow, Director of the National Institute on Drug Abuse and a long-time collaborator on neuroimaging research at Brookhaven Lab.

The study, published in the September 9, 2009, issue of the , also has important implications for treatment. "Finding ways to address the underlying reward-system deficit could improve the direct clinical outcome of ADHD, and potentially reduce the likelihood of other negative consequences of this condition," said study co-author Gene-Jack Wang, chair of Brookhaven's medical department.

Prior to this study, it was not clear whether people with ADHD had abnormalities in the brain's dopamine-mediated motivation/reward system. Previous studies were relatively small and may have been complicated by the fact that some ADHD patients had undergone treatments, or had a history of drug abuse or other conditions that can affect the system.

To strengthen the statistics and control for these factors, the current study looked at 53 adult ADHD patients who had never received treatment and 44 healthy control subjects — all of whom had been carefully screened to eliminate potentially confounding variables.

The scientists used positron emission tomography (PET) to measure two markers of the dopamine system — dopamine receptors, to which the chemical messenger binds to propagate the "reward" signal, and dopamine transporters, which take up and recycle excess dopamine after the signal is sent.

Lying in a PET scanner, each patient was injected with a minute amount of a "radiotracer" compound — a chemical labeled with a radioactive form of carbon and designed to bind specifically to one of the targets. Different tracers were used for each target, and patients were scanned for each at separate times. By detecting the signal from the radiotracers, the PET machine can measure the receptor and transporter locations and concentrations in various parts of the brain.

The results clearly showed that, relative to the healthy control subjects, the ADHD patients had lower levels of dopamine receptors and transporters in the accumbens and midbrain — two key regions of the brain directly involved in processing motivation and reward. In addition, the measurements of dopamine markers correlated with measures of behavior and clinical observations of ADHD symptoms, such as reduced levels of attention as measured by standard psychological tests.

"Our findings imply that these deficits in the dopamine reward pathway play a role in the symptoms of inattention in ADHD and could underlie these patients' abnormal responses to reward," Volkow said.

"This pathway plays a key role in reinforcement, motivation, and in learning how to associate various stimuli with rewards," she continued. "Its involvement in ADHD supports the use of interventions to enhance the appeal and relevance of school and work tasks to improve performance.

"Our results also support the continued use of stimulant medications — the most common pharmacological treatment for ADHD — which have been shown to increase attention to cognitive tasks by elevating brain dopamine," she said.

The findings may also help explain why ADHD patients are more likely than control subjects to develop drug-abuse disorders and conditions such as obesity.

Said Wang: "Other studies from our group suggest that patients who abuse drugs or overeat may be unconsciously attempting to compensate for a deficient reward system by boosting their dopamine levels. Understanding how deficits in the dopamine system contribute to ADHD and finding ways to improve the functioning of the reward system could help mitigate these troubling consequences in the patient population."

Source: DOE/Brookhaven National Laboratory

Explore further: Long-term effects of battle-related 'blast plus impact' concussive TBI in US military

add to favorites email to friend print save as pdf

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.

Cocaine's effects on brain metabolism may contribute to abuse

Feb 18, 2008

Many studies on cocaine addiction - and attempts to block its addictiveness - have focused on dopamine transporters, proteins that reabsorb the brain's "reward" chemical once its signal is sent. Since cocaine blocks dopamine ...

Protein on 'speed' linked to ADHD

Jul 08, 2008

A genetic change in the dopamine transporter – one of the brain's dopamine-handling proteins – makes it behave as if amphetamine is present and "run backward," Vanderbilt University Medical Center investigators report ...

1 sleepless night increases dopamine in the human brain

Aug 19, 2008

Just one night without sleep can increase the amount of the chemical dopamine in the human brain, according to new imaging research in the August 20 issue of The Journal of Neuroscience. Because drugs that increase dopami ...

Recommended for you

Turning off depression in the brain

14 hours ago

Scientists have traced vulnerability to depression-like behaviors in mice to out-of-balance electrical activity inside neurons of the brain's reward circuit and experimentally reversed it – but there's ...

Rapid whole-brain imaging with single cell resolution

15 hours ago

A major challenge of systems biology is understanding how phenomena at the cellular scale correlate with activity at the organism level. A concerted effort has been made especially in the brain, as scientists are aiming to ...

User comments : 0

More news stories

Leeches help save woman's ear after pit bull mauling

(HealthDay)—A pit bull attack in July 2013 left a 19-year-old woman with her left ear ripped from her head, leaving an open wound. After preserving the ear, the surgical team started with a reconnection ...

Scientists tether lionfish to Cayman reefs

Research done by U.S. scientists in the Cayman Islands suggests that native predators can be trained to gobble up invasive lionfish that colonize regional reefs and voraciously prey on juvenile marine creatures.

Venture investments jump to $9.5B in 1Q

Funding for U.S. startup companies soared 57 percent in the first quarter to a level not seen since 2001, as venture capitalists piled more money into an increasing number of deals, according to a report due out Friday.

White House updating online privacy policy

A new Obama administration privacy policy out Friday explains how the government will gather the user data of online visitors to WhiteHouse.gov, mobile apps and social media sites. It also clarifies that ...