A study recently published by CMU psychologist Mark Reilly, left, along with a team of CMU experimental psychology graduate students, has brought the researchers one step closer to understanding and treating impulsivity in children with ADHD. (Credit: Photo by Robert Barclay, CMU)

ADHD is one of the most commonly diagnosed chronic psychiatric conditions in today's school-aged children and is based on such behavioral criteria as impulsivity, hyperactivity, inattention and learning disabilities.

CMU associate professor of psychology Mark Reilly, along with experimental psychology graduate students Andrew Fox and Dennis Hand, recently published a study that investigated impulsivity in two strains of rat. The spontaneously hypertensive rat has been proposed as a rodent model of ADHD because the rats have behavioral characteristics similar to those seen in humans diagnosed with ADHD. In the study, the impulsivity of spontaneously hypertensive rats was compared to their parent strain without hypertension, Wistar-Kyoto rats, using a self-control choice task that was originally developed in humans.

The study concluded that the spontaneously hypertensive rats were more impulsive than the Wistar-Kyoto rats by demonstrating greater preference for smaller, immediate food rewards over larger, delayed ones. The results suggest that, like humans, the spontaneously hypertensive rats are hypersensitive to delayed consequences; they do not wait for better outcomes.

"A good animal model of impulsivity will lead to a better understanding of ADHD," said Reilly. "This experiment is a more directed look at impulsivity. We are investigating the behavioral characteristics of the spontaneously hypertensive rats in order to assist in developing pharmacological and behavioral therapies to be used in the treatment of ADHD."

Reilly's research strengthens the validity of the spontaneously hypertensive rat as a model of ADHD. The procedure used in this study may lend itself well to testing the effects of next generation ADHD drugs and commonly prescribed psychomotor stimulants such as methylphenidate, also known as Ritalin.