Adults with attention deficit hyperactivity disorder often struggle with choices that require weighing potential rewards against negative consequences. A new experiment reveals that a common stimulant medication improves these choices specifically by helping individuals pay more attention to the potential costs of their actions. The research was published in Psychological Medicine.
Attention deficit hyperactivity disorder is a neurodevelopmental condition characterized by inattention, hyperactivity, and impulsive behavior. People with this diagnosis frequently experience difficulties with real-life decisions, which can manifest as reckless driving, substance abuse, and risky sexual behavior. Every day, humans navigate choices that require balancing the positive aspects of an action against its negative aspects. Buying a new phone brings the benefit of better technology but carries the cost of having less money for groceries.
Neurobiological theories suggest that the disorder involves atypical functioning of dopamine and norepinephrine, which are chemical messengers in the brain that help regulate attention, reward processing, and cognitive effort. Stimulant medications like methylphenidate, often sold under the brand name Ritalin, increase the availability of these chemicals in the brain. While researchers know that stimulants generally improve decision-making, the exact psychological mechanisms driving this improvement have remained elusive.
Mads Lund Pedersen, a psychologist at the University of Oslo, and a team of colleagues conducted a study to break down the specific components of decision-making. They wanted to know if medication helps people by increasing their sensitivity to rewards, heightening their awareness of costs, or simply altering the amount of time they spend thinking before they act.
To answer these questions, the research team recruited 61 adults diagnosed with attention deficit hyperactivity disorder and 63 healthy control participants. The study utilized a double-blind, placebo-controlled crossover design. The participants with the diagnosis completed the testing twice, once after taking their standard dose of methylphenidate and once after taking an inactive placebo pill. Neither the participants nor the researchers knew which pill was administered on which day. The healthy control participants also completed the testing twice but did not receive any medication.
During the experiment, participants engaged in a computer-based task designed to test how they integrate costs and benefits. First, they completed a training phase where they learned to associate six different shapes with specific numerical rewards and six different colors with specific numerical costs. After learning these associations, they moved on to the main testing phase.
In the testing phase, the computer presented participants with a colored shape for a few seconds. The participants had to mentally combine the benefit value of the shape and the cost value of the color to determine the net value. If the net value was positive, the correct choice was to accept the offer. If the net value was negative, the correct choice was to reject it.
The researchers analyzed the behavioral data using a mathematical framework called the drift diffusion model. This model separates the fast, split-second process of making a choice into distinct cognitive components. One component is the drift rate, which measures how quickly and efficiently the brain accumulates evidence about the choice. Another component is the decision threshold, which represents the amount of information a person requires before they commit to an action, often referred to as the speed-accuracy tradeoff. A third component is non-decision time, which accounts for the physical time it takes to see the image on the screen and press the button.
The results showed that when participants with the diagnosis were given the placebo, they were less accurate than the healthy control group. The mathematical model revealed that the unmedicated participants had a lower drift rate, meaning they processed information about both the costs and the benefits less efficiently. They also exhibited a narrower decision threshold, meaning they acted on less information and responded prematurely.
The researchers also compared how the different groups weighed the positive and negative information. The healthy control participants naturally allowed the cost of the stimuli to influence their decisions more heavily than the benefits. The unmedicated participants with attention deficit hyperactivity disorder showed the reverse pattern, demonstrating a stronger sensitivity to the benefits than to the costs.
Administration of methylphenidate changed how the participants processed the information. The medication caused an increase in the drift rate, but this improvement was highly selective. The drug improved how efficiently the participants accumulated evidence about the costs, while leaving their sensitivity to the benefits entirely unchanged. By boosting cost sensitivity, the medication shifted the overall balance of their decision-making closer to the pattern seen in the healthy control group.
The medication also produced some unexpected effects. Instead of increasing the decision threshold to make participants wait for more information, the drug narrowed the threshold slightly further. However, the medication also increased the participants’ non-decision time. The researchers suggest that the participants might have spent this extra fraction of a second visually encoding the images, which could have improved the accuracy of their stimulus representations and contributed to the higher drift rate observed under medication.
The researchers analyzed individual differences among the participants who had the diagnosis. They found that individuals who reported more severe symptoms in their daily lives had the lowest sensitivity to costs when they were unmedicated. Among those taking medication, higher prescribed doses of methylphenidate were associated with both a stronger sensitivity to costs and a wider decision threshold.
The study includes several limitations regarding how the medication might be acting on the brain. The drug could be improving basic learning and memory rather than the actual moment of decision-making. Because participants had to memorize the values of the shapes and colors during the training phase, the stimulant might simply help them remember those specific values more reliably during the test.
Alternatively, participants might have used simple mental arithmetic to subtract the cost from the benefit. Stimulant medication could enhance this working memory skill independently of how the brain naturally weighs risks and rewards. The study also excluded individuals with severe comorbid psychiatric conditions, meaning the results might not apply to people who have additional severe mental health disorders. Finally, because the medication can cause noticeable physical sensations, some participants might have guessed when they received the active drug, which can influence behavioral performance through expectations.
Future research could separate these potential mechanisms by providing the values directly on the screen, removing the need for participants to memorize the shapes and colors beforehand.
The study, “Selective enhancement of cost sensitivity by methylphenidate in adult ADHD: a randomized placebo-controlled trial,” was authored by Mads Lund Pedersen, Athanasia M. Mowinckel, Sigurd Ziegler, Mats Fredriksen, Atle Bjørnerud, Tor Endestad, and Guido Biele.