Attention deficit hyperactivity disorder, or ADHD, has been called one of the most common learning disorders. In 2019, experts estimated that roughly 5-7% of the world’s children meet the criteria for an ADHD diagnosis. 1 Despite its prevalence, it has historically been a much-misunderstood disorder. One that is sometimes attributed to poor parenting or character defects. However, as the field of neuroscience has grown, our understanding of the neurobiology of ADHD has evolved as well. Many of the problematic characteristics often associated with ADHD have a basis in the brain.
Mapping the Neurobiology of ADHD
The field of neurobiology studies the relationship between the brain and behavior. More specifically, it’s the study of the components of the nervous system and its organization into functional circuits that process information and influence behavior.
We now recognize that the neurobiological changes present in the brain of a child with ADHD cause difficulties in many parts of life.
From a neurobiological perspective, researchers and doctors have turned their focus toward what exactly makes someone with ADHD different. By identifying which specific tasks children with ADHD typically struggle to perform, scientists can home in on the areas of the brain responsible for those tasks. The hope among doctors is that the more we learn about the ADHD brain, the more targeted our future treatments may become.
For this reason, researchers have set about finding the specific ways in which children with ADHD behave differently from their peers. By observing differences in performance on cleverly designed tests, scientists have begun to sketch an outline of the exact cognitive impairments that characterize ADHD.
Neurobiology of ADHD: Identifying Impairments
A truly exhaustive list of every specific way a child with ADHD might show decreased cognitive performance would be much too long to place here. And we should realize that no two children with ADHD experience the same obstacles. We find many different ADHD symptoms in kids. For some, attention is the main issue. For others, hyperactivity and impulse control are the main stumbling blocks.
Nonetheless, researchers have identified the following areas of concern: selective attention, sustained attention, cognitive flexibility, time processing, working memory, response precision, and response inhibition. 2 Many of us can recognize some of these terms. Some of us may have even used an app or read a book, hoping to improve our cognitive skills in these areas. Other skills may seem a little foreign.
The Array of Cognitive Issues
For the sake of clarity and accuracy, let’s review some definitions.
- Selective attention is the ability to process information from one source while disregarding information from other distracting sources.
- Sustained attention is the ability to carry out a task or process information continuously without showing decreased performance as time passes.
- Cognitive flexibility is the ability to switch quickly from one task to a different one without making errors.
- Time processing is the ability to estimate accurately how much time has passed without looking at a clock.
- Working memory is the ability to absorb and later reproduce information over brief intervals without making mistakes.
- Response precision is the ability to only respond to events at the assigned place and time.
- Response inhibition is the ability to suppress actions or behaviors that are not appropriate for a given task. 2
The lived experiences of countless children and parents provide plenty of testimony to support scientists’ conclusions. Children with ADHD are neurobiologically predisposed to struggle a bit with the cognitive tasks outlined above.
This knowledge allows for parents, teachers, and others to adjust their expectations and teaching methods appropriately. For example, due to their diminished capacity to correctly identify how much time has passed during a particular activity, students with ADHD are frequently given extra time during exams. Outside of the classroom, this time perception issue provides context for frustrated parents who otherwise wouldn’t understand how a five-minute video game break became an hour-long break!
A Closer Look
Categorizing the specific cognitive disabilities present in ADHD has another benefit. By monitoring cerebral blood flow or electrical activity as children utilize the cognitive skills outlined above, scientists can now observe distinct differences in the ADHD brain. Listing the neural circuitry implicated in each deficit is beyond our scope. Also, neurobiology is constantly evolving, so some of the details to follow may change over time. With that said, the mechanisms underlying sustained attention and time processing are worthy of a brief review.
Scientists have identified portions of the brain they believe to be responsible for sustained attention. These include the norepinephrine-releasing nerves of the locus coeruleus and the acetylcholine-releasing nerves of the nucleus basalis. When a child performs tasks requiring sustained attention, both regions send their respective neurotransmitter signals to the prefrontal cortex. 2
When it comes to time processing, scientists haven’t yet identified the specific neurotransmitters involved. However, researchers have identified circuits between the parietal cortex, cerebellum, and prefrontal cortex which they believe to be involved. Interestingly, drugs like Adderall, which promote norepinephrine activity in the regions discussed above, have shown the ability to specifically improve sustained attention and time processing in people with ADHD. 2
Looking Towards the Future
As we look to the future, we can imagine how neurobiological research will light the way to more focused treatments. Someday soon, ADHD treatments may even be customizable based upon which cognitive defects are most prominent. Therefore, doctors and researchers are hopeful about the next generation of targeted medicines and therapies for children with ADHD. Parents of children with ADHD should know that the future for ADHD treatment looks bright!
- “Attention-Deficit/Hyperactivity Disorder – Level 3 Cause.” Institute for Health Metrics and Evaluation, 15 Oct. 2020, www.healthdata.org/results/gbd_summaries/2019/attention-deficit-hyperactivity-disorder-level-3-cause.
- Mueller A, Hong DS, Shepard S, Moore T. Linking ADHD to the Neural Circuitry of Attention. Trends Cogn Sci. 2017;21(6):474-488. doi:10.1016/j.tics.2017.03.009
Guest Contributor: Dr. Martin Duggan, DO, is a licensed physician in the United States who frequently writes for scientific and lay audiences.