Researchers say ADHD medications in high doses can impair memory

Researchers at the University of Wisconsin studying the implications of using methylphenidate, more commonly known by the “trade name” Ritalin, on the behavior of those taking the medication for attention deficit hyperactivity disorder found the drug can often cause people to be less successful in cognitive tasks.

Abby Rajala, the lead author on the study, said the results of the research published last week in the Journal of Cognitive Neuroscience resembled similar findings of a 1977 study that has until now not been replicated. Both studies found a low dose of the drug stimulated cognitive performance in subjects with ADHD while a high dose served to diminish hyperactive behavior and impair performance on a memory test.

For the ongoing project that began in 2007, Rajala, a UW graduate student in the Neuroscience Training Program, also worked with Luis Populin, a neuroscience professor at the UW School of Medicine and Public Health.

She said their team has been evaluating rhesus macaque monkeys, which are the mammals with the closest brain structure and function to humans, on cognitive performance tasks with and without the aid of the drug methylphenidate.

In the investigation, three monkeys were taught to perform a spatial learning task in which they focused on a dot in the middle of a screen before a “target” dot flashed on the screen elsewhere. Successive trials made the monkeys wait varying amounts of time before needing to shift their eyes to the target on the screen.

When a monkey correctly identified that location, they were rewarded with a sip of water. This functioned as a positive reinforcement for their performance, reflecting operant conditioning, Rajala said.

She said more correct trials were observed from monkeys given a low dose of methylphenidate than their high-dose counterparts. Yet despite the lack of a reward, she said the monkeys on high doses continued to perform the task for much longer than those on low doses.

Despite getting the task “wrong” or not receiving any real incentive to keep going, the monkeys on high doses worked for up to seven hours.

Brad Postle, associate professor of psychology at UW, said this study emphasizes the subtleties of the dose-dependent phenomenon. Although teachers may prefer students on a higher dose due to improved classroom behavior, he said it essentially turns children into “zombies.”

“Too much of the drug on board basically makes you dumber,” Postle said.

Rajala noted that while many college students take high doses of Adderall and Ritalin when cramming for exams, they most likely are giving themselves a “false sense of security to study and remember better.”

Jeffrey Henriques, a psychology professor who assisted in the research, said the most intriguing piece about the work is the suggestion that medication may not actually help children as students.

“The monkey data seems to suggest that we are just making them docile and continuing at a task that they’re not being successful at,” he said. “So yes, the teacher is happy that the child is not disrupting class anymore, but have we really helped the child learn anything?”