By Anne Harding
NEW YORK (Reuters Health) - Stimulant drugs like Ritalin work by "fine-tuning" neuron activity in the prefrontal cortex, the part of the brain responsible for filtering out distractions and helping people to focus on tasks, new research in rats suggests.

Little is known about how Ritalin and related drugs actually work, researchers point out in the journal Biological Psychiatry.

To investigate, Dr. Craig Berridge of the University of Wisconsin-Madison and his colleague David Devilbiss attached tiny electrodes to individual neurons in the brains of normal rats and watched how different doses of the drug affected neuron activity.

Small doses that, in previous experiments, were shown to enhance cognitive function, increased the responsiveness of individual neurons within the prefrontal cortex to signals coming from the hippocampus, a part of the brain that regulates memory and emotion.

And when groups of neurons in the prefrontal cortex were working in well-organized networks, the small doses of Ritalin enhanced this activity, but suppressed the activity of less organized networks.

People without attention problems are increasingly using Ritalin to boost their cognitive function, Berridge noted, and his findings show why the drug is useful for this purpose, as well as effective in treating most children with attention deficit-hyperactivity disorder (ADHD).

"We drink coffee for the same reasons," he said. "Most of the world takes coffee to help stay focused on target, and these drugs are highly effective at that. If they were completely risk-free you would probably see a broader use."

However, Berridge noted, the drug does carry a risk of addiction. Understanding how it works could help in the development of less risky drugs for treating attention problems, he added.

SOURCE: Biological Psychiatry 2008.