For most of the adults I see with ADHD, inattentive symptoms are the ones that cause the most difficulties at work, at home, and in intimate and social relationships. Inattentive symptoms can make it difficult to stay focused, follow through on tasks, and manage time effectively. In the 21st century, multiple research studies have highlighted the role of the brain's default mode network (DMN) in these symptoms using functional magnetic resonance imaging (fMRI).
What is the Default Mode Network?
The default mode network (DMN) is a network of brain regions that are active when we are at rest and not focused on the outside world. This network is thought to be involved in various functions, including daydreaming, self-referential thinking, and recalling memories. Essentially, the DMN is active during our "default" state—when our mind wanders and we are not engaged in a specific task.
What is the Task Positive Network?
The task-positive network (TPN), also known as the central-executive network, is a network of brain regions that are activated when we are engaged in focused, goal-directed activities. The TPN is involved in tasks that require attention, problem-solving, and active thinking.
When the TPN is active, it helps us concentrate on the task at hand, process information, and make decisions. The TPN works in opposition to the DMN; typically, when one network is active, the other is suppressed. Therefore, this balance between the DMN and TPN is important for effective cognitive functioning.
The DMN and Inattentiveness in ADHD
In people with ADHD, research suggests that the DMN may not deactivate appropriately when attention is required for a task. This can lead to a sort of "cross-talk", or interference between the DMN and the TPN, which is responsible for focused, goal-directed activities.
Here are a few ways this may manifest:
Mind-Wandering/Internal Distractibility: People with ADHD often experience frequent mind-wandering, where their thoughts drift away from the task they are supposed to be focusing on. This internal distractibility may be due to the DMN staying active even when attention should be directed elsewhere.
Difficulty Starting Tasks: Initiating tasks can be challenging for those with ADHD, perhaps because the DMN can dominate, leading to procrastination and an inability to shift into a focused, task-oriented state.
Challenges with Task-Switching: The DMN can interfere with the TPN network, making it harder to transition from one task to another efficiently.
A small study involving 18 children with ADHD compared to a matched group of children without ADHD revealed interesting findings about the DMN. When the children with ADHD were off medication (methylphenidate), their DMN showed less reduction during a task compared to the children without ADHD. However, when the children were either medicated or motivated by an incentive to perform well on the task, their DMN activity resembled that of the control group, indicating a similar ability to suppress the DMN during task-focused activities given the right conditions.
These results suggest that both stimulant medication and increased motivation can help align the DMN function of children with ADHD closer to those without ADHD. This likely reflects an improved ability to focus and reduce internal distractions. The study's findings resonate with everyday experiences, such as how approaching deadlines or engaging in more preferred tasks can enhance focus. For me, it also raises intriguing questions about how the DMN operates during periods of hyperfocus in individuals with ADHD, where attention becomes intensely concentrated, often on a highly engaging task.
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Conclusion
The default mode network appears to play a significant role in the inattentive symptoms of ADHD. By recognising the influence of the DMN, a person with ADHD may feel less to blame for their difficulty in modulating their attention, and may be able to find strategies to work to minimise distractions when they really need to start a task or switch between tasks (e.g. utilising medication or incentives as in the study cited above).
This article by ADHD expert psychiatrist Dr Ned Hallowell, who has ADHD himself, offers an introduction to the default mode network in ADHD
This is the reference for the study of 18 children mentioned in the text above: Liddle, E. B., Hollis, C., Batty, M. J., Groom, M. J., Totman, J. J., Liotti, M., Scerif, G., & Liddle, P. F. (2011). Task-related default mode network modulation and inhibitory control in ADHD: effects of motivation and methylphenidate. Journal of Child Psychology and Psychiatry, 52(7), 761-771.
And this is a study finding differences in the default mode network in a meta-analysis of functional magnetic imaging studies in both children and adults: Cortese, S., Kelly, C., Chabernaud, C., Proal, E., Di Martino, A., Milham, M. P., & Castellanos, F. X. (2012). Toward systems neuroscience of ADHD: a meta-analysis of 55 fMRI studies. American Journal of Psychiatry, 169(10), 1038-1055.
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