November 14, 2019

It has been known that a widely-used attention-deficit/hyperactivity disorder (ADHD) drug affected the brain—but the specifics of those effects hadn’t been fully understood until now.

Luis Populin, PhD, professor of neuroscience in the School of Medicine and Public Health at the University of Wisconsin-Madison, and colleagues at the Wisconsin National Primate Research Center (WiNPRC) have demonstrated for the first time the complete actions of Ritalin (methylphenidate, or MPH) on various regions and chemicals in the brain.

Ritalin can increase dopamine, a brain chemical associated with reward-motivated behavior, and is typically prescribed to children with ADHD. This increase changes the way the brain makes connections among its various networks, including those that affect attention, learning and motor processes.

In the study, the scientists used positron-emission tomography (PET) imaging to study the brains of three conscious adult male rhesus monkeys. Using simultaneous functional magnetic resonance imaging (fMRI), the researchers were able to directly link increases in dopamine from MPH to changes in functional connections between the caudate—the part of the brain critical to learning through storing and processing memories—and the prefrontal, hippocampal and motor regions.

Studies in humans using fMRI have explored how MPH alters the brain, but some of those studies have reported increases in dopamine after MPH administration, while others have reported decreases. The researchers noted that this may be because most studies used a single dose of the drug and different experimental conditions.

In this study, they “bridged the gap” between neurochemistry and functional organization by simultaneously measuring changes in extracellular dopamine using PET. Additionally, the doses given to the monkeys were comparable to those resulting in equivalent blood levels of the medication when used therapeutically in children.

“Our study sheds much needed light on understanding the mechanisms underlying the effects of therapeutically relevant doses of MPH,” said Populin, adding that future studies may go even further to understand how the drug works in the context of cognition. “We hope we can expand on this research to better understand how the drug works in the brain while it’s actually processing different things.”

Populin noted that the more scientists discover about the processes, the more effective doctors can be in prescribing ADHD medications for children.

Back to top