How Ritalin focuses children's minds

3 June 2006

HERE’S a paradox. Why does an amphetamine-like stimulant have a calming effect on children with attention deficit hyperactivity disorder (ADHD)?

Experiments with rats may have provided the answer. It seems that methylphenidate – better known as Ritalin and commonly used to treat ADHD – pulls off two apparently contradictory feats. First it raises levels of the neurotransmitter noradrenalin, which probably helps sharpen senses, and at the same time it dulls the brain’s reactions to unwanted distractions.

“It probably helps the animal focus on what’s new and not be distracted by what’s familiar,” says Candice Drouin, who led the team at Drexel University in Philadelphia. “That’s what happens in children with ADHD: they pay attention to too many things.”

Drouin and her team took measurements of the rats’ primary somatosensory cortex, a brain region that registers signals from whiskers. In rats on methylphenidate, levels of noradrenalin were up to twice as high there, suggesting they would be more keenly attuned to whisker signals. In humans, that would equate to better processing of information. The drug also blocked secondary responses to each whisker movement, indicating that the animals paid no further attention to the tweaked whisker.

The paper will appear in the Journal of Neurophysiology.