Performance on a problem-solving task is no better and sometimes worse than under placebo.
Bad news for all the uni students relying on their cousins’ ADHD medication to get them through exams.
A new study out of the University of Melbourne and Cambridge, published in Science Advances, suggests any cognitive improvement after taking “smart” drugs is illusory at best: you may feel you’re working harder, but you won’t be working smarter.
The team set out to quantify the benefit, or not, of methylphenidate, dextroamphetamine and modafinil for solving a computationally difficult problem known as the knapsack task: participants have to choose objects of varying “value” to put into a knapsack so as to maximise the overall value without exceeding a certain weight.
Forty young adults took part in four sessions a week or more apart in which they were randomised to receive one of the three drugs or placebo, and put through the task a number of times at varying levels of difficulty with a time limit of four minutes.
As a group, the drugs had no significant effect on the subjects’ ability to get the right answer.
But measuring the value of the knapsacks, the drugs actually decreased performance.
The drugs increased both the time spent on each instance of the task and the number of moves made in each instance, making it difficult to measure speed. So the drugs improved motivation if you define motivation simply by the number of moves made.
When they analysed individuals’ performance, they found worse quality of effort (= the average gain in value of a knapsack per move) under all three drugs compared with placebo.
The researchers then divided subjects into above-average and below-average performance on placebo and compared their performance on the smart drugs. They found an interesting flip: those who were above average on placebo all did worse on the various drugs. Those who were below average without the drugs improved their performance with them – but only because, the authors speculate, they spent more time on each task and had more goes at it.
There was greater randomness in knapsack-filling attempts under the drug conditions than under placebo: “This, together with the finding that exploration (number of moves) increases, suggests that participants’ approach to solving a hard problem … becomes less systematic under drugs; in other words, while drugs increase persistence, they appear to reduce the quality of effort.” In more probabilistic tasks, where random exploration can help, you might expect to see more benefit from these drugs, the authors say.
Finally, the team also gave subjects the CANTAB battery of neurocognitive performance tests and found almost no correlation with knapsack performance: they “failed to predict individual drug effects in the knapsack task from scores on the CANTAB tasks or from drug effects in the CANTAB tasks”. But comparing their results with the drugs’ effects on cognition of ADHD patients, they say: “the evidence from healthy participants appears to be an extension of that of the clinical population, so that ADHD may not be a categorical disorder but instead better described as a dimensional disorder” – and they leave it at that.
Good luck to all those cramming for their mid-year exams the old-fashioned way: lots of awful coffee and insufficient sleep.
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