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New insights into reward processing could aid understanding of ADHD and addiction

Researchers from King’s College London have identified a coordinated network of brain activity which may explain how the brain anticipates and processes rewards.

The study, published today in Proceedings of National Academy of Sciences (PNAS), also highlights a novel gene, known as ‘VPS4A’, that appears to regulate levels of dopamine in key areas of the brain.

This genetic mechanism may explain how dopamine levels increase when people anticipate a reward and why problems with reward processing are found in people with various mental disorders, including attention deficit hyperactivity disorder (ADHD) and addictions such as alcohol abuse.

It is possible that these impairments may involve different components of the reward process, including brain activity during the anticipation of future rewards. Previous research has been limited to very selected brain structures, whereas this study is the largest and most comprehensive analysis to date of brain activity during reward anticipation.

According to the study authors, a better understanding of these brain networks and how they are regulated could help with identifying therapeutic targets for mental health disorders such as ADHD and alcohol abuse.

Using data collected by IMAGEN, a large European research project led by King’s College London, the researchers examined brain regions engaged by reward anticipation in 1,544 adolescents.

Reward anticipation was assessed through brain scans of adolescents during a task where cues indicate that either no reward, a small reward or a large reward might be won during the trial. Participants were then asked to respond to a target in order to gain the reward.

By measuring blood oxygen-levels in the brain, the researchers compared brain activity during the anticipation of rewards with that of activity when no rewards were anticipated. They discovered a network of brain activity related to reward processing in the cerebral cortex, which is responsible for intelligence, language, memory and consciousness, as well as regions below the cerebral cortex (‘subcortical’ brain areas).

They also looked at associations between brain activity and behavioural outcomes related to ADHD and addiction, including measures of hyperactivity and lifetime alcohol consumption. The researchers found that reduced activity in the striatum - a region of the brain known to be dysfunctional in people with ADHD - was associated with higher levels of hyperactivity. However, this association was only observed in boys.

Finally, the study team selected adolescents with very high hyperactivity scores and compared them to individuals with no indication of hyperactivity. They found that the correlation between hyperactivity and activity in a subcortical region of the brain was twice as strong in extreme cases of hyperactivity, compared to those with no symptoms of hyperactivity.

Professor Gunter Schumann, senior author of the paper from the MRC Social, Genetic and Developmental Psychiatry (SGDP) Centre at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN), King’s College London, and Coordinator of the IMAGEN project, said: ‘We already know that reward-related disorders, such as ADHD and alcohol abuse, often occur simultaneously. Our findings go some way towards explaining how this relationship is driven by common neural mechanisms, despite the fact that both are currently diagnosed and treated differently.

‘We have also discovered a gene that appears to regulate dopamine activity observed in dysfunctional reward processing, which may account for the enduring nature of related mental health disorders.

‘These insights may be helpful in identifying what is causing ADHD and alcohol abuse at a neural level, and could be important for highlighting novel treatment targets for techniques such as brain stimulation.’

Notes to editors

Jia, T et al (2016) The neural basis of reward anticipation and its genetic determinants Proceedings of the National Academy of Sciences

For further media information please contact Jack Stonebridge, Press Officer, Institute of Psychiatry, Psychology & Neuroscience, King’s College London 020 7848 5377