New research into the ’‘stop’ brain chemical could improve treatment of such conditions as attention deficit hyperactivity disorder (ADHD).

How do we stop ourselves doing inappropriate actions, like blurting out impulsive comments, jumping red lights, or rushing in front of cars? Samuel Chamberlain, Professor Barbara Sahakian and colleagues have shown that this ability is controlled by a particular brain chemical.

In their novel study published in Science on 10th February 2006, the researchers showed that increasing a brain chemical called noradrenaline made healthy volunteers better at stopping or inhibiting their actions.

They were able to increase brain noradrenaline by giving the drug atomoxetine. This is the first clear demonstration of how stopping is controlled by a chemical in the brain, and therefore has important implications for drug development.

The research team used a computerised test that involved pressing a left or right key as quickly as possible in response to arrows on a computer screen. When a beep noise sounded, this signalled to volunteers that they should stop or inhibit their responses. This is a simplified form of stopping, which can be related to everyday behaviour such as being able to stop at red lights.

Many neuropsychiatric patients, particularly those with attention deficit hyperactivity disorder (ADHD), have difficulties inhibiting their inappropriate behaviours. Atomoxetine, which was licensed for the treatment of ADHD in 2004, works by increasing noradrenaline. Therefore, the Cambridge group believes that their study sheds light on the mechanism of action of the drug in the clinical treatment of impulsive behaviour in ADHD.

Samuel Chamberlain, research fellow and student doctor at the Cambridge School of Clinical Medicine, said: “These results are important because difficulties stopping inappropriate behaviour cause some of the greatest problems for patients with ADHD and their families.”

Barbara Sahakian, Professor of Clinical Neuropsychology at Cambridge University and co-head of the Wellcome Trust and Medical Research Council funded research team said: “We think that this is a key discovery, because understanding how this drug acts to produce impulse control will allow us to develop more effective treatments for patients showing impulsive behaviour.”

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