A new study sheds light on the impact of ADHD on motivation and the effectiveness of amphetamine-based medications
In a recent study published in Journal of NeuroscienceResearchers have found that individuals with attention-deficit hyperactivity disorder (ADHD) show decreased motivation to engage in stressful activities, both cognitive and physical, which can be significantly improved with amphetamine-containing medications.
ADHD, a common behavioral disorder, is often associated with difficulty maintaining attention, hyperactivity, and impulsivity. Traditionally, ADHD has been viewed primarily through the lens of these symptoms. However, recent research suggests that motivation, especially the desire to put in effort, plays a crucial role in ADHD. This new study was conducted to explore how individuals with ADHD differ in their motivation for stressful tasks compared to those without the disorder, and to evaluate the effectiveness of commonly prescribed ADHD medications in addressing these differences.
“The hallmark of ADHD is thought to be low levels of motivation — in particular, a decreased willingness to invest effort,” said study author Trevor Chung, a future fellow at the Australian Research Council, head of the Cognitive Neuroscience Laboratory, and associate professor at Harvard University. “. Monash University.
“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, although motivation is important in current frameworks of ADHD, Very few studies have examined the willingness of individuals with ADHD to engage in cognitive or physical effortful behavior. We therefore designed a task to test whether motivation is indeed lower in ADHD and, if so, whether medications Amphetamine-based medications commonly used to treat ADHD can bring him back.
The study included 44 participants: 20 individuals diagnosed with ADHD and 24 individuals without the condition (referred to as the control group). The ADHD group included individuals who were being treated with amphetamine-based medications such as dexamfetamine or its prodrug lisdexamfetamine. Participants with ADHD were tested twice – once when they were taking their medication regularly and once after a 72-hour period without medication, to understand the effect of these medications on their motivation levels.
To measure motivation, the researchers developed a unique experiment divided into two main parts: a training (or reinforcement) phase and a choice phase. In the reinforcement phase, participants were trained on tasks that required cognitive (mental) or physical effort.
For example, the cognitive task involved detecting specific letters in rapidly changing sequences, which increased its difficulty. The physical task required participants to exert different levels of force using a hand-held device. After training, the choice phase measured participants’ willingness to engage in these stressful tasks by giving them a choice between a low-effort/low-reward option and a variable high-effort/high-reward option.
On the cognitive effort task, researchers found no significant differences in performance between ADHD participants and the control group, or within the ADHD group when taking or stopping the medication. This means that ADHD does not inherently affect the ability to perform cognitive tasks. However, on the physical effort task, those with ADHD showed a greater ability to sustain effort when taking medication compared to those not taking medication. However, there was no significant difference in the ability to obtain rewards, suggesting that the drug did not simply make the task easier to perform.
The results of the selection phase were particularly striking. When medication was discontinued, individuals with ADHD showed less motivation to invest effort in cognitive and physical tasks compared to the control group. This effect was particularly evident at higher levels of cognitive effort and lower levels of physical effort. On the other hand, when taking medication, the ADHD group’s motivation increased significantly, closely aligning with the control group’s motivation levels.
“Some authors have hypothesized that cognitive symptoms of ADHD may be driven by a decreased desire to engage in effortful cognitive behavior,” Chung said. “Our data confirmed that cognitive motivation is indeed lower in ADHD compared to controls, but also showed that ADHD was associated with lower levels of motivation in the physical domain.”
These findings provide concrete evidence that motivation, especially the desire to exert effort, is a key component of ADHD, and not just a side effect of other symptoms. Furthermore, it shows that medications containing amphetamine, which are commonly prescribed to treat ADHD, are effective in enhancing motivation in these individuals.
“The motivation to invest cognitive and physical effort is lower in individuals with ADHD than in those without the condition,” Chung told PsyPost. “It is reassuring that this decrease in stimulation can be improved with currently available stimulant medications.”
However, it is important to note some limitations of the study. First, the sample size was relatively small, and larger studies are needed to confirm these results. In addition, the study focused primarily on the effects of medications containing amphetamine, and it is not clear whether similar results would be observed with other types of ADHD medications. The study also did not delve into psychological aspects of motivation, such as the role of personal interests or the influence of long-term goals, which can be important factors in understanding motivation in ADHD.
“Amphetamines are stimulant medications that increase the activity of dopamine and norepinephrine in the brain,” Chung 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 elucidated.”
The study, “Amphetamines Improve Motivation to Invest Effort in Attention Deficit/Hyperactivity Disorder,” was authored by Trevor T.J. Chung, Erika Fortunato, and Mark A. Belgrove.