Rhesus Pieces: Of Reading, Writing, and Ritalin

The debate is at least as old as Clinton vs. Dole.  Are children identified as having ADHD being overmedicated?  Our visionhelp.com colleague Dr. Carole Hong and I explored this to some degree in our article in California Optometry a few years ago.  My purpose here is not to enter the debate about whether psycho-stimulants like Ritalin are “good” or “bad”.  Like any other medication it can be used or abused.  I will note that it seems we’ve gotten awfully cavalier in this country about accepting anecdotal evidence on the off-label prescribing of a variety of drugs.  And in other countries Ritalin use as an “upper” has become so widespread that it’s now available over-the-counter.

What intrigues me is the attention being paid to a new study just published in the Journal of Cognitive Neuroscience that suggests a new way at looking at what the drug does, or doesn’t do.   The abstract of the paper indicates that the study investigated the effects of methylphenidate on working memory performance, impulsivity, response accuracy and precision, and the ability to stay on task in rhesus monkeys using an oculomotor delayed response task.

Three monkeys were taught to focus on a central dot on a screen, while a target dot flashed nearby. The monkeys were taught that they could earn a sip of water by waiting until the central dot switched off, and then looking at the location of the now-vanished target dot.  Essentially the researchers were using a peripheral awareness paradigm.

Methylphenidate (Ritalin)  affected task performance in an inverted-U manner in all three subjects tested. The improvements resulted from a reduction in premature responses and, importantly, not from improvement in the memory of target location. The length of time subjects participated in each session was also affected dose dependently. However, the dose at which the length of participation was maximally increased significantly impaired performance on the working memory task. This dissociation of effects has implications for the treatment of ADHD, for the nonprescription use of methylphenidate for cognitive enhancement, and for furthering the basic understanding of the neural substrate underlying these processes.

Here’s a key statement by one of the study’s co-authors, Luis Populin, an associate professor of neuroscience at the University of Wisconsin-Madison School of Medicine and Public Health, as quoted in Science Daily:

“Drug dosages may be set high enough to reduce the characteristic hyperactivity of ADHD, but some children say that makes them feel less creative and spontaneous; more like a robot. If learning drops off as it did in our study, that dose may not be best for them. Our monkeys actually did act like robots at the higher doses, keeping at it for up to seven hours even though their performance was so low.”

So what does Ritalin do?  It doesn’t necessarily improve memory, as once thought.  It can reduce hyperactivity and that certainly makes the child more conveniently manageable in the classroom and potentially less of a behavior problem.  College students and adults are more likely to have the cognitive capacity to decide whether it is a cognitive enhancement and if so, at what doses.  But what is a safe and effective dose for a young children for whom the side-effects can often be as disabling as the intended effects?

At the very least this paper gives pause to the movement afoot to dish out Ritalin tablets as if they emanated from Pez Dispensers.  Let the debates continue!

– Leonard J. Press, O.D., FCOVD, FAAO

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