In a recent study published in the Journal of Neuroscience, researchers discovered that individuals diagnosed with Attention-Deficit/Hyperactivity Disorder (ADHD) exhibit diminished motivation to partake in both cognitive and physical activities requiring effort. This motivation deficit, however, was found to be significantly ameliorated by amphetamine-based medications.
ADHD, a frequently diagnosed behavioral disorder, is commonly characterized by issues involving attention, hyperactivity, and impulsiveness. Until recently, ADHD was predominantly analyzed through the lens of these symptoms. Nevertheless, the latest research highlights the importance of motivation, particularly the willingness to exert effort, in the realm of ADHD. Consequently, the just-published investigation aimed to scrutinize the disparities in individuals with ADHD’s motivation for demanding tasks compared to those without the disorder, and to evaluate the efficacy of commonly prescribed ADHD medications in addressing these differences.
Lead study author Trevor Chong, who is a head of the Cognitive Neurology Laboratory and an associate professor at Monash University, noted, “A hallmark of ADHD is thought to be reduced levels of motivation – in particular, a lower willingness to invest effort.”
Chong further expounded, “Effort can be experienced across multiple domains – for example, it can be perceived cognitively (such as when studying for an exam), or physically (such as when training for a race). Importantly, despite the importance of motivation to current frameworks of ADHD, very few studies have examined the willingness of individuals with ADHD to exert cognitively or physically effortful behavior. We therefore designed a task to specifically test whether motivation is indeed lower in ADHD and, if so, whether amphetamine-based medications that are commonly used to treat ADHD can restore it.”
The study, which entailed 44 participants – 20 individuals diagnosed with ADHD and 24 without it (the control group) – included individuals using amphetamine-based drugs like dexamfetamine or its prodrug, lisdexamfetamine. The researchers administered tests to the ADHD group twice – once while the participants were taking their regular medication and once after a 72-hour period without it, aiming to discern the impact of these medications on the participants’ motivation levels.
To gauge motivation, the researchers developed a unique experiment involving a training (or reinforcement) phase and a choice phase. During the reinforcement phase, participants were instructed in tasks encompassing either cognitive or physical effort.
For example, the cognitive task involved detecting specific letters in rapidly changing sequences, while the physical task necessitated varying levels of force using a hand-held device. Subsequently, the choice phase discerned the participants’ willingness to engage in these effortful tasks by presenting them with a low-effort/low-reward option as well as a high-effort/high-reward option.
The researchers’ findings revealed no significant performance disparities between the ADHD participants and the control group in the cognitive effort task. This suggests that ADHD does not inherently impact the ability to perform cognitive tasks. Conversely, in the physical effort task, individuals with ADHD exhibited a greater ability to sustain effort while on medication, compared to being off medication. However, there was no notable difference in their ability to obtain rewards, indicating that the medication did not simply make the task easier to perform.
The results of the choice phase were particularly remarkable. When not taking their medication, individuals with ADHD displayed less motivation to invest effort in both cognitive and physical tasks relative to the control group. This effect was especially pronounced at higher cognitive effort levels and lower physical effort levels. Conversely, when taking their medication, the motivation of the ADHD group notably increased, closely aligning with the motivation levels of the control group.
Chong elucidated, “Some authors have postulated that the cognitive symptoms of ADHD may be driven by a lower willingness to engage in cognitively effortful behavior. Our data confirmed that cognitive motivation is indeed lower in ADHD relative to controls, but also showed that ADHD was associated with lower levels of motivation in the physical domain.”
These findings establish conclusive evidence that motivation, particularly the willingness to exert effort, plays a pivotal role in ADHD, rather than merely being a byproduct of other symptoms. Moreover, it demonstrates the efficacy of commonly prescribed amphetamine-based medications in enhancing motivation in individuals with ADHD.
“The motivation to invest cognitive and physical effort is lower in individuals with ADHD relative to those without the condition,” Chong shared with PsyPost. “Reassuringly, this reduction in motivation can be improved with currently available stimulant medications.”
Nonetheless, it’s essential to acknowledge certain limitations of the study. Primarily, the sample size was relatively small, warranting larger studies to corroborate these findings. Additionally, the study predominantly focused on the effects of amphetamine-based medications, leaving it ambiguous whether similar results would be observed with other types of ADHD medications. The study also did not deeply investigate the psychological aspects of motivation, such as the impact of personal interests and long-term goals, which could be crucial in comprehending motivation in ADHD.
“Amphetamines are stimulant medications that increase the activity of dopamine and noradrenaline in the brain,” Chong explained. “The fact that amphetamines improve the willingness to invest effort is evidence that these neurotransmitters play an important role in motivated behavior. However, motivation is a complex neurobiological process, and the role of other neurotransmitters, such as serotonin, remains to be clarified.”
The study, “Amphetamines Improve the Motivation to Invest Effort in Attention-Deficit/Hyperactivity Disorder,” was penned by Trevor T.-J. Chong, Erika Fortunato, and Mark A. Bellgrove. You can access the full study here.
