Children and adolescents with attention-deficit/hyperactivity disorder (ADHD) appear to show early and stable disruptions in a key brain system involved in emotional and cognitive processing, according to new research published in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging. The findings suggest that ADHD involves differences in how emotional and cognitive brain circuits are physically wired during development. Although these differences are subtle, they could play a role in shaping the severity of symptoms across childhood and adolescence.
ADHD has increasingly been conceptualized as a disorder that affects the brain’s connectivity. Many studies have focused on the brain’s outer cortical regions, such as the frontal lobes, which are involved in attention and executive function. However, less is known about how deeper brain structures, like those in the limbic system, develop in children with ADHD.
The limbic system helps regulate emotion and integrates emotional signals with cognitive processes. It is also implicated in behavioral regulation, impulse control, and mood—all areas where people with ADHD often experience difficulties. Emotional dysregulation is especially common in ADHD and can affect quality of life. Given the limbic system’s role in emotion and behavior, the researchers aimed to better understand how its white matter—bundles of nerve fibers that connect brain regions—develops in youth with ADHD.
Longitudinal brain imaging research allows scientists to examine how brain structures change over time. By focusing on the limbic system and using more advanced imaging techniques than in past research, the authors of this study hoped to uncover developmental patterns that may help explain why some symptoms of ADHD persist or worsen during adolescence.
“Most research on ADHD brain development has focused on the outer regions of the brain, especially the frontal and striatal areas linked to attention and control,” said study author Michael Connaughton of the Department of Psychiatry at Trinity College Dublin.
“We wanted to look deeper – literally – into the limbic system, the brain’s emotional core that connects feeling, motivation, and focus. These regions have been difficult to study because of their complexity and location, but new MRI analysis techniques now let us see them with much finer detail. That opened the door to an important question: how do emotion-related brain pathways mature in ADHD as children move through adolescence?”
The researchers analyzed brain imaging data from 169 children and adolescents between the ages of 9 and 14. Among them, 72 had been diagnosed with ADHD, while 97 served as a comparison group without the disorder. Each participant underwent advanced diffusion MRI scans at three different time points spaced about 18 months apart. This approach allowed researchers to track changes in brain white matter over time.
“A key strength of this study was that ADHD was confirmed at multiple time points, showing that participants met diagnostic criteria both early and later in development,” Connaughton noted. “This repeated confirmation is crucial for developmental research – it ensures we’re capturing stable features of ADHD rather than temporary fluctuations that can occur as children grow and symptoms change.”
The researchers used an advanced brain imaging technique called diffusion kurtosis imaging to examine the structure of white matter in the brain. This method tracks how water molecules move through brain tissue. In healthy white matter, which consists of tightly packed, insulated nerve fibers, water tends to move in a highly organized way. When the structure is less orderly, water movement becomes more random.
One specific measurement, called kurtosis anisotropy, captures this level of organization. Higher kurtosis anisotropy values indicate that the white matter fibers are well-organized and likely well-myelinated, meaning they are coated with a protective layer that helps electrical signals travel efficiently. Lower values suggest that the white matter may be less developed or less efficient at supporting fast communication between brain regions.
The researchers focused on five major white matter tracts in the limbic system, including the cingulum bundle, which connects regions involved in both cognition and emotion. They also constructed brain network models to assess how different parts of the limbic system were interconnected in each participant.
Compared to the control group, the children with ADHD showed lower kurtosis anisotropy in both the left and right cingulum bundles. These reductions were present across all three time points, suggesting that the white matter differences were not due to temporary fluctuations but instead reflected a stable, early-emerging feature of ADHD. The pattern of white matter development followed a typical trajectory over time, but those with ADHD started out at a lower baseline and did not catch up to their peers.
“Individuals with ADHD showed stable reductions in limbic system white matter microstructural organisation, specifically lower kurtosis anisotropy in the bilateral cingulum bundle, across childhood and adolescence,” Connaughton told PsyPost.
Interestingly, the overall number and efficiency of connections within the limbic system did not significantly differ between the ADHD and control groups when considered as a whole. However, when the researchers looked at symptom severity within the ADHD group, a clearer picture emerged. Children and adolescents with more severe ADHD symptoms tended to have lower network density and reduced routing efficiency in their limbic system connections.
“What stood out most was that connectivity within the limbic system network predicted symptom severity rather than diagnosis,” Connaughton said. “This reinforces the view of ADHD as a dimensional condition, existing along a continuum rather than as a categorical divide.”
The relationship between limbic system connectivity and symptom severity was not explained by differences in the cingulum bundle, suggesting that both local microstructure and broader network organization may contribute to ADHD symptoms in distinct ways.
The differences observed in the study were relatively small in size, but they were consistent. “They aren’t large enough for clinical prediction, but in neurodevelopment, small differences across interconnected systems can still influence symptom severity and presentation,” Connaughton explained.
“Overall, the findings indicate that ADHD involves early, stable disruptions in limbic white matter development, particularly within the cingulum, and that reductions in white matter interconnecting limbic regions become more pronounced in individuals with more severe ADHD symptoms.”
Rather than pointing to a single brain abnormality, the results support the idea that ADHD involves distributed, small-scale differences across multiple systems. These differences may arise early in life and contribute to how symptoms unfold over time.
“These results don’t point to a single ‘ADHD biomarker,’” Connaughton said. “They reflect group- level trends, not diagnostic markers, and should be seen as part of a larger developmental picture that combines genetics, environment, and experience.”
The study offers important insights but also has some limitations. One issue is that the limbic system does not have a universally agreed-upon anatomical definition. Different studies may include or exclude certain regions, which can complicate comparisons across research.
The age range studied was also relatively narrow, focusing on the transition from late childhood into early adolescence. Some individuals with ADHD may show delayed brain development that catches up later in adolescence or early adulthood. Extending the research to cover a wider age range could help clarify whether the differences observed here persist, worsen, or diminish over time.
“We aim to track these developmental changes across the lifespan, extending our work into late adolescence and early adulthood when brain connectivity continues to evolve,” Connaughton explained. “By following individuals over longer periods and integrating imaging with genetic and behavioural data, we can begin to see how early brain differences unfold, stabilize, or adapt over time. The goal is to build a lifespan model of ADHD that helps both patients and clinicians understand why symptoms persist or remit across life.”
The study, “Limbic System White Matter in Children and Adolescents with ADHD: A Longitudinal Diffusion MRI Analysis,” was authored by Michael Connaughton, Alexander Leemans, Timothy J. Silk, Vicki Anderson, Erik O’Hanlon, Robert Whelan, and Jane McGrath.
