July 9, 2008 | 8 comments

Ritalin Dose Changes Effect

Research with rats finds that Ritalin at low doses encourages neurons to fire together, but at high doses it's just another stimulant. Christopher Intagliata reports

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[The following is an exact transcript of this podcast.]

Doctors prescribe Ritalin to hyperactive kids to calm them down and increase their attention span. And college kids have taken to using Ritalin to concentrate when they hit the books. But it hasn’t been clear how the drug boosts focus. Now a paper in the journal Biological Psychiatry suggests how it might work.

Neuroscientists dosed rats with Ritalin and had them perform the kind of working memory task ADHD patients have trouble with. At the same time they measured neural activity with tiny electrodes implanted in the rats’ brains. At low doses, Ritalin primarily affected the prefrontal cortex, jacking up its sensitivity to signals coming in from the hippocampus. And here’s how the drug seemed to help with attention—it strengthened choruses of neurons firing together and put a damper on scattered, uncoordinated activity.

But at high doses, the prefrontal cortex tuned out, and Ritalin’s effects were similar to those of other stimulants. The rats lost their cognitive edge and they became hyperactive, sniffing and licking repetitively. So Ritalin shows you can indeed have too much of a good thing—to the point of distraction.

—Christopher Intagliata

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