Prescription medicines used to treat attention deficit hyperactivity disorder (ADHD) may primarily work by increasing alertness and interest in tasks, rather than directly enhancing the brain’s ability to focus, a new study has suggested.
ADHD is a neurodevelopmental condition characterised by short attention spans and restless, impulsive behaviour. Stimulant drugs—available in India under brand names such as Addwise and prescribed by psychiatrists—are believed to act by raising levels of brain chemicals including norepinephrine and dopamine, thereby improving focus and impulse control.
In the study, researchers, including those from Washington University in the US, analysed functional magnetic resonance imaging (fMRI) scans of nearly 5,800 children aged between 8 and 11. The scans captured brain activity when the children were not engaged in any specific task.
The findings, published in the journal Cell, show for the first time that stimulant medications mainly affect brain regions linked to reward and wakefulness, rather than areas traditionally associated with attention, the researchers said.
The medicines were also found to produce brain activity similar to the effects of good sleep, counteracting changes linked to sleep deprivation. Children with ADHD are known to experience sleep problems, including difficulty falling asleep and restless sleep.
“Essentially, we found that stimulants pre-reward our brains and allow us to keep working at things that wouldn't normally hold our interest -- like our least favourite class in school, for example,” said co-lead researcher Nico U. Dosenbach, professor of neurology at Washington University’s School of Medicine.
Co-lead researcher Benjamin Kay, a paediatric neurologist and assistant professor at the same institution, said, “I prescribe a lot of stimulants as a child neurologist, and I've always been taught that they facilitate attention systems to give people more voluntary control over what they pay attention to.”
“But we've shown that's not the case. Rather, the improvement we observe in attention is a secondary effect of a child being more alert and finding a task more rewarding, which naturally helps them pay more attention to it,” Kay said.
Kay added that the findings highlight the need to address inadequate sleep alongside the use of stimulant medication when evaluating children for ADHD.
The researchers compared patterns of brain connectivity in children who took prescription stimulants on the day of their scan with those who did not. All participants were part of the larger Adolescent Brain Cognitive Development (ABCD) study, which is tracking more than 11,000 children across the United States.
“Taking stimulants reversed the effects of sleep deprivation on connectivity and school grades. Connectivity was also changed in salience and parietal memory networks, which are important for dopamine-mediated, reward-motivated learning, but not the brain's attention systems,” the authors wrote.
Compared with children with ADHD who did not take stimulants, those who did were reported by parents to have better school grades and also performed better on cognitive tests conducted as part of the study. The greatest cognitive gains were observed among children with more severe ADHD, the researchers said.
However, the study found that stimulant medications did not lead to cognitive benefits for all children. The drugs were not associated with improved performance in neurotypical children who were getting sufficient sleep, the team added.