A SYSTEMS NEUROSCIENCE APPROACH TO ADHD

For decades, the prevailing model of ADHD focused almost exclusively on the prefrontal-striatal-cerebellar circuit, which governs executive function. While this model is supported by significant evidence, it often ignores findings in other brain regions and fails to capture the full complexity of the disorder. This paper argues for a shift toward a systems neuroscience approach, utilizing resting-state functional magnetic resonance imaging (R-fMRI) to map how large-scale neural networks interact in the ADHD brain.

R-fMRI allows researchers to observe the brain's intrinsic functional architecture by measuring spontaneous, low-frequency fluctuations in blood oxygenation levels. These fluctuations reveal robust, reproducible networks that persist even when a person is not performing a specific task. By analyzing these networks, researchers can move beyond the "narrow-angle" view provided by task-based imaging and observe how different brain systems—such as the default, frontoparietal, and attentional networks—communicate and compete for resources.

Instead of focusing on isolated regions, the authors evaluate ADHD through the lens of several critical systems:

• Frontoparietal Network: Often called the executive control circuit, this system is crucial for goal-directed behavior. Hypoactivation here is a consistent finding in ADHD, contributing to deficits in inhibition and working memory.
• Default Network: This network is most active during rest and self-referential thought. In ADHD, the default network often fails to suppress appropriately during tasks, which may explain the characteristic attentional lapses and behavioral inconsistency seen in patients.
• Dorsal and Ventral Attentional Networks: These systems manage top-down control and the monitoring of salient stimuli. Abnormalities in these networks, particularly in parietal regions, are linked to difficulties in shifting attention.
• Visual and Motor Networks: Emerging evidence suggests that primary visual and motor cortices are also involved in ADHD, challenging the traditional view that the disorder is limited to executive control areas.